| Message ID | 20220407031525.2368067-7-yuzhao@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Multi-Gen LRU Framework | expand |
() On Thu, Apr 7, 2022 at 3:16 PM Yu Zhao <yuzhao@google.com> wrote: > > To avoid confusion, the terms "promotion" and "demotion" will be > applied to the multi-gen LRU, as a new convention; the terms > "activation" and "deactivation" will be applied to the active/inactive > LRU, as usual. > > The aging produces young generations. Given an lruvec, it increments > max_seq when max_seq-min_seq+1 approaches MIN_NR_GENS. The aging > promotes hot pages to the youngest generation when it finds them > accessed through page tables; the demotion of cold pages happens > consequently when it increments max_seq. The aging has the complexity > O(nr_hot_pages), since it is only interested in hot pages. Promotion > in the aging path does not require any LRU list operations, only the > updates of the gen counter and lrugen->nr_pages[]; demotion, unless as > the result of the increment of max_seq, requires LRU list operations, > e.g., lru_deactivate_fn(). > > The eviction consumes old generations. Given an lruvec, it increments > min_seq when the lists indexed by min_seq%MAX_NR_GENS become empty. A > feedback loop modeled after the PID controller monitors refaults over > anon and file types and decides which type to evict when both types > are available from the same generation. > > Each generation is divided into multiple tiers. Tiers represent > different ranges of numbers of accesses through file descriptors. A > page accessed N times through file descriptors is in tier > order_base_2(N). Tiers do not have dedicated lrugen->lists[], only > bits in folio->flags. In contrast to moving across generations, which > requires the LRU lock, moving across tiers only involves operations on > folio->flags. The feedback loop also monitors refaults over all tiers > and decides when to protect pages in which tiers (N>1), using the > first tier (N=0,1) as a baseline. The first tier contains single-use > unmapped clean pages, which are most likely the best choices. The > eviction moves a page to the next generation, i.e., min_seq+1, if the > feedback loop decides so. This approach has the following advantages: > 1. It removes the cost of activation in the buffered access path by > inferring whether pages accessed multiple times through file > descriptors are statistically hot and thus worth protecting in the > eviction path. > 2. It takes pages accessed through page tables into account and avoids > overprotecting pages accessed multiple times through file > descriptors. (Pages accessed through page tables are in the first > tier, since N=0.) > 3. More tiers provide better protection for pages accessed more than > twice through file descriptors, when under heavy buffered I/O > workloads. > > Server benchmark results: > Single workload: > fio (buffered I/O): +[40, 42]% > IOPS BW > 5.18-rc1: 2463k 9621MiB/s > patch1-6: 3484k 13.3GiB/s > > Single workload: > memcached (anon): +[44, 46]% > Ops/sec KB/sec > 5.18-rc1: 771403.27 30004.17 > patch1-6: 1120643.70 43588.06 > > Configurations: > CPU: two Xeon 6154 > Mem: total 256G > > Node 1 was only used as a ram disk to reduce the variance in the > results. > > patch drivers/block/brd.c <<EOF > 99,100c99,100 > < gfp_flags = GFP_NOIO | __GFP_ZERO | __GFP_HIGHMEM; > < page = alloc_page(gfp_flags); > --- > > gfp_flags = GFP_NOIO | __GFP_ZERO | __GFP_HIGHMEM | __GFP_THISNODE; > > page = alloc_pages_node(1, gfp_flags, 0); > EOF > > cat >>/etc/systemd/system.conf <<EOF > CPUAffinity=numa > NUMAPolicy=bind > NUMAMask=0 > EOF > > cat >>/etc/memcached.conf <<EOF > -m 184320 > -s /var/run/memcached/memcached.sock > -a 0766 > -t 36 > -B binary > EOF > > cat fio.sh > modprobe brd rd_nr=1 rd_size=113246208 > swapoff -a > mkfs.ext4 /dev/ram0 > mount -t ext4 /dev/ram0 /mnt > > mkdir /sys/fs/cgroup/user.slice/test > echo 38654705664 >/sys/fs/cgroup/user.slice/test/memory.max > echo $$ >/sys/fs/cgroup/user.slice/test/cgroup.procs > fio -name=mglru --numjobs=72 --directory=/mnt --size=1408m \ > --buffered=1 --ioengine=io_uring --iodepth=128 \ > --iodepth_batch_submit=32 --iodepth_batch_complete=32 \ > --rw=randread --random_distribution=random --norandommap \ > --time_based --ramp_time=10m --runtime=5m --group_reporting > > cat memcached.sh > modprobe brd rd_nr=1 rd_size=113246208 > swapoff -a > mkswap /dev/ram0 > swapon /dev/ram0 > > memtier_benchmark -S /var/run/memcached/memcached.sock \ > -P memcache_binary -n allkeys --key-minimum=1 \ > --key-maximum=65000000 --key-pattern=P:P -c 1 -t 36 \ > --ratio 1:0 --pipeline 8 -d 2000 > > memtier_benchmark -S /var/run/memcached/memcached.sock \ > -P memcache_binary -n allkeys --key-minimum=1 \ > --key-maximum=65000000 --key-pattern=R:R -c 1 -t 36 \ > --ratio 0:1 --pipeline 8 --randomize --distinct-client-seed > > Client benchmark results: > kswapd profiles: > 5.18-rc1 > 40.53% page_vma_mapped_walk > 20.37% lzo1x_1_do_compress (real work) > 6.99% do_raw_spin_lock > 3.93% _raw_spin_unlock_irq > 2.08% vma_interval_tree_subtree_search > 2.06% vma_interval_tree_iter_next > 1.95% folio_referenced_one > 1.93% anon_vma_interval_tree_iter_first > 1.51% ptep_clear_flush > 1.35% __anon_vma_interval_tree_subtree_search > > patch1-6 > 35.99% lzo1x_1_do_compress (real work) > 19.40% page_vma_mapped_walk > 6.31% _raw_spin_unlock_irq > 3.95% do_raw_spin_lock > 2.39% anon_vma_interval_tree_iter_first > 2.25% ptep_clear_flush > 1.92% __anon_vma_interval_tree_subtree_search > 1.70% folio_referenced_one > 1.68% __zram_bvec_write > 1.43% anon_vma_interval_tree_iter_next > > Configurations: > CPU: single Snapdragon 7c > Mem: total 4G > > Chrome OS MemoryPressure [1] > > [1] https://chromium.googlesource.com/chromiumos/platform/tast-tests/ > > Signed-off-by: Yu Zhao <yuzhao@google.com> > Acked-by: Brian Geffon <bgeffon@google.com> > Acked-by: Jan Alexander Steffens (heftig) <heftig@archlinux.org> > Acked-by: Oleksandr Natalenko <oleksandr@natalenko.name> > Acked-by: Steven Barrett <steven@liquorix.net> > Acked-by: Suleiman Souhlal <suleiman@google.com> > Tested-by: Daniel Byrne <djbyrne@mtu.edu> > Tested-by: Donald Carr <d@chaos-reins.com> > Tested-by: Holger Hoffstätte <holger@applied-asynchrony.com> > Tested-by: Konstantin Kharlamov <Hi-Angel@yandex.ru> > Tested-by: Shuang Zhai <szhai2@cs.rochester.edu> > Tested-by: Sofia Trinh <sofia.trinh@edi.works> > Tested-by: Vaibhav Jain <vaibhav@linux.ibm.com> > --- > include/linux/mm_inline.h | 24 ++ > include/linux/mmzone.h | 41 ++ > kernel/bounds.c | 2 +- > mm/Kconfig | 11 + > mm/swap.c | 42 ++ > mm/vmscan.c | 805 +++++++++++++++++++++++++++++++++++++- > mm/workingset.c | 119 +++++- > 7 files changed, 1040 insertions(+), 4 deletions(-) > > diff --git a/include/linux/mm_inline.h b/include/linux/mm_inline.h > index 9abd72a95462..8a8f87b72540 100644 > --- a/include/linux/mm_inline.h > +++ b/include/linux/mm_inline.h > @@ -119,6 +119,19 @@ static inline int lru_gen_from_seq(unsigned long seq) > return seq % MAX_NR_GENS; > } > > +static inline int lru_hist_from_seq(unsigned long seq) > +{ > + return seq % NR_HIST_GENS; > +} > + > +static inline int lru_tier_from_refs(int refs) > +{ > + VM_BUG_ON(refs > BIT(LRU_REFS_WIDTH)); > + > + /* see the comment on MAX_NR_TIERS */ > + return order_base_2(refs + 1); > +} > + > static inline bool lru_gen_is_active(struct lruvec *lruvec, int gen) > { > unsigned long max_seq = lruvec->lrugen.max_seq; > @@ -164,6 +177,15 @@ static inline void lru_gen_update_size(struct lruvec *lruvec, struct folio *foli > __update_lru_size(lruvec, lru, zone, -delta); > return; > } > + > + /* promotion */ > + if (!lru_gen_is_active(lruvec, old_gen) && lru_gen_is_active(lruvec, new_gen)) { > + __update_lru_size(lruvec, lru, zone, -delta); > + __update_lru_size(lruvec, lru + LRU_ACTIVE, zone, delta); > + } > + > + /* demotion requires isolation, e.g., lru_deactivate_fn() */ > + VM_BUG_ON(lru_gen_is_active(lruvec, old_gen) && !lru_gen_is_active(lruvec, new_gen)); > } > > static inline bool lru_gen_add_folio(struct lruvec *lruvec, struct folio *folio, bool reclaiming) > @@ -229,6 +251,8 @@ static inline bool lru_gen_del_folio(struct lruvec *lruvec, struct folio *folio, > gen = ((new_flags & LRU_GEN_MASK) >> LRU_GEN_PGOFF) - 1; > > new_flags &= ~LRU_GEN_MASK; > + if (!(new_flags & BIT(PG_referenced))) > + new_flags &= ~(LRU_REFS_MASK | LRU_REFS_FLAGS); > /* for shrink_page_list() */ > if (reclaiming) > new_flags &= ~(BIT(PG_referenced) | BIT(PG_reclaim)); > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h > index bde05427e2bb..c8a7ceee7a0a 100644 > --- a/include/linux/mmzone.h > +++ b/include/linux/mmzone.h > @@ -347,12 +347,34 @@ enum lruvec_flags { > #define MIN_NR_GENS 2U > #define MAX_NR_GENS 4U > > +/* > + * Each generation is divided into multiple tiers. Tiers represent different > + * ranges of numbers of accesses through file descriptors. A page accessed N > + * times through file descriptors is in tier order_base_2(N). A page in the > + * first tier (N=0,1) is marked by PG_referenced unless it was faulted in > + * though page tables or read ahead. A page in any other tier (N>1) is marked > + * by PG_referenced and PG_workingset. > + * > + * In contrast to moving across generations which requires the LRU lock, moving > + * across tiers only requires operations on folio->flags and therefore has a > + * negligible cost in the buffered access path. In the eviction path, > + * comparisons of refaulted/(evicted+protected) from the first tier and the > + * rest infer whether pages accessed multiple times through file descriptors > + * are statistically hot and thus worth protecting. > + * > + * MAX_NR_TIERS is set to 4 so that the multi-gen LRU can support twice of the > + * categories of the active/inactive LRU when keeping track of accesses through > + * file descriptors. It requires MAX_NR_TIERS-2 additional bits in folio->flags. > + */ > +#define MAX_NR_TIERS 4U > + > #ifndef __GENERATING_BOUNDS_H > > struct lruvec; > > #define LRU_GEN_MASK ((BIT(LRU_GEN_WIDTH) - 1) << LRU_GEN_PGOFF) > #define LRU_REFS_MASK ((BIT(LRU_REFS_WIDTH) - 1) << LRU_REFS_PGOFF) > +#define LRU_REFS_FLAGS (BIT(PG_referenced) | BIT(PG_workingset)) > > #ifdef CONFIG_LRU_GEN > > @@ -361,6 +383,16 @@ enum { > LRU_GEN_FILE, > }; > > +#define MIN_LRU_BATCH BITS_PER_LONG > +#define MAX_LRU_BATCH (MIN_LRU_BATCH * 128) > + > +/* whether to keep historical stats from evicted generations */ > +#ifdef CONFIG_LRU_GEN_STATS > +#define NR_HIST_GENS MAX_NR_GENS > +#else > +#define NR_HIST_GENS 1U > +#endif > + > /* > * The youngest generation number is stored in max_seq for both anon and file > * types as they are aged on an equal footing. The oldest generation numbers are > @@ -380,6 +412,15 @@ struct lru_gen_struct { > struct list_head lists[MAX_NR_GENS][ANON_AND_FILE][MAX_NR_ZONES]; > /* the sizes of the above lists */ > unsigned long nr_pages[MAX_NR_GENS][ANON_AND_FILE][MAX_NR_ZONES]; > + /* the exponential moving average of refaulted */ > + unsigned long avg_refaulted[ANON_AND_FILE][MAX_NR_TIERS]; > + /* the exponential moving average of evicted+protected */ > + unsigned long avg_total[ANON_AND_FILE][MAX_NR_TIERS]; > + /* the first tier doesn't need protection, hence the minus one */ > + unsigned long protected[NR_HIST_GENS][ANON_AND_FILE][MAX_NR_TIERS - 1]; > + /* can be modified without holding the LRU lock */ > + atomic_long_t evicted[NR_HIST_GENS][ANON_AND_FILE][MAX_NR_TIERS]; > + atomic_long_t refaulted[NR_HIST_GENS][ANON_AND_FILE][MAX_NR_TIERS]; > }; > > void lru_gen_init_lruvec(struct lruvec *lruvec); > diff --git a/kernel/bounds.c b/kernel/bounds.c > index e08fb89f87f4..10dd9e6b03e5 100644 > --- a/kernel/bounds.c > +++ b/kernel/bounds.c > @@ -24,7 +24,7 @@ int main(void) > DEFINE(SPINLOCK_SIZE, sizeof(spinlock_t)); > #ifdef CONFIG_LRU_GEN > DEFINE(LRU_GEN_WIDTH, order_base_2(MAX_NR_GENS + 1)); > - DEFINE(LRU_REFS_WIDTH, 0); > + DEFINE(LRU_REFS_WIDTH, MAX_NR_TIERS - 2); > #else > DEFINE(LRU_GEN_WIDTH, 0); > DEFINE(LRU_REFS_WIDTH, 0); > diff --git a/mm/Kconfig b/mm/Kconfig > index 4595fc654181..c40777d098a8 100644 > --- a/mm/Kconfig > +++ b/mm/Kconfig > @@ -909,6 +909,7 @@ config ANON_VMA_NAME > area from being merged with adjacent virtual memory areas due to the > difference in their name. > > +# multi-gen LRU { > config LRU_GEN > bool "Multi-Gen LRU" > depends on MMU > @@ -917,6 +918,16 @@ config LRU_GEN > help > A high performance LRU implementation to overcommit memory. > > +config LRU_GEN_STATS > + bool "Full stats for debugging" > + depends on LRU_GEN > + help > + Do not enable this option unless you plan to look at historical stats > + from evicted generations for debugging purpose. > + > + This option has a per-memcg and per-node memory overhead. > +# } > + > source "mm/damon/Kconfig" > > endmenu > diff --git a/mm/swap.c b/mm/swap.c > index a6870ba0bd83..6a5203f18b0a 100644 > --- a/mm/swap.c > +++ b/mm/swap.c > @@ -405,6 +405,43 @@ static void __lru_cache_activate_folio(struct folio *folio) > local_unlock(&lru_pvecs.lock); > } > > +#ifdef CONFIG_LRU_GEN > +static void folio_inc_refs(struct folio *folio) > +{ > + unsigned long refs; > + unsigned long old_flags, new_flags; > + > + if (folio_test_unevictable(folio)) > + return; > + > + /* see the comment on MAX_NR_TIERS */ > + do { > + new_flags = old_flags = READ_ONCE(folio->flags); > + > + if (!(new_flags & BIT(PG_referenced))) { > + new_flags |= BIT(PG_referenced); > + continue; > + } > + > + if (!(new_flags & BIT(PG_workingset))) { > + new_flags |= BIT(PG_workingset); > + continue; > + } > + > + refs = new_flags & LRU_REFS_MASK; > + refs = min(refs + BIT(LRU_REFS_PGOFF), LRU_REFS_MASK); > + > + new_flags &= ~LRU_REFS_MASK; > + new_flags |= refs; > + } while (new_flags != old_flags && > + cmpxchg(&folio->flags, old_flags, new_flags) != old_flags); > +} > +#else > +static void folio_inc_refs(struct folio *folio) > +{ > +} > +#endif /* CONFIG_LRU_GEN */ > + > /* > * Mark a page as having seen activity. > * > @@ -417,6 +454,11 @@ static void __lru_cache_activate_folio(struct folio *folio) > */ > void folio_mark_accessed(struct folio *folio) > { > + if (lru_gen_enabled()) { > + folio_inc_refs(folio); > + return; > + } > + > if (!folio_test_referenced(folio)) { > folio_set_referenced(folio); > } else if (folio_test_unevictable(folio)) { > diff --git a/mm/vmscan.c b/mm/vmscan.c > index 37dd5d1c3d07..bb3d705c5282 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -1275,9 +1275,11 @@ static int __remove_mapping(struct address_space *mapping, struct folio *folio, > > if (folio_test_swapcache(folio)) { > swp_entry_t swap = folio_swap_entry(folio); > - mem_cgroup_swapout(folio, swap); > + > + /* get a shadow entry before mem_cgroup_swapout() clears folio_memcg() */ > if (reclaimed && !mapping_exiting(mapping)) > shadow = workingset_eviction(folio, target_memcg); > + mem_cgroup_swapout(folio, swap); > __delete_from_swap_cache(&folio->page, swap, shadow); > xa_unlock_irq(&mapping->i_pages); > put_swap_page(&folio->page, swap); > @@ -2649,6 +2651,9 @@ static void prepare_scan_count(pg_data_t *pgdat, struct scan_control *sc) > unsigned long file; > struct lruvec *target_lruvec; > > + if (lru_gen_enabled()) > + return; > + > target_lruvec = mem_cgroup_lruvec(sc->target_mem_cgroup, pgdat); > > /* > @@ -2974,11 +2979,38 @@ static bool can_age_anon_pages(struct pglist_data *pgdat, > * shorthand helpers > ******************************************************************************/ > > +#define DEFINE_MAX_SEQ(lruvec) \ > + unsigned long max_seq = READ_ONCE((lruvec)->lrugen.max_seq) > + > +#define DEFINE_MIN_SEQ(lruvec) \ > + unsigned long min_seq[ANON_AND_FILE] = { \ > + READ_ONCE((lruvec)->lrugen.min_seq[LRU_GEN_ANON]), \ > + READ_ONCE((lruvec)->lrugen.min_seq[LRU_GEN_FILE]), \ > + } > + > #define for_each_gen_type_zone(gen, type, zone) \ > for ((gen) = 0; (gen) < MAX_NR_GENS; (gen)++) \ > for ((type) = 0; (type) < ANON_AND_FILE; (type)++) \ > for ((zone) = 0; (zone) < MAX_NR_ZONES; (zone)++) > > +static int folio_lru_gen(struct folio *folio) > +{ > + unsigned long flags = READ_ONCE(folio->flags); > + > + return ((flags & LRU_GEN_MASK) >> LRU_GEN_PGOFF) - 1; > +} > + > +static int folio_lru_tier(struct folio *folio) > +{ > + int refs; > + unsigned long flags = READ_ONCE(folio->flags); > + > + refs = (flags & LRU_REFS_FLAGS) == LRU_REFS_FLAGS ? > + ((flags & LRU_REFS_MASK) >> LRU_REFS_PGOFF) + 1 : 0; > + > + return lru_tier_from_refs(refs); > +} > + > static struct lruvec __maybe_unused *get_lruvec(struct mem_cgroup *memcg, int nid) > { > struct pglist_data *pgdat = NODE_DATA(nid); > @@ -2999,6 +3031,754 @@ static struct lruvec __maybe_unused *get_lruvec(struct mem_cgroup *memcg, int ni > return pgdat ? &pgdat->__lruvec : NULL; > } > > +static int get_swappiness(struct lruvec *lruvec, struct scan_control *sc) > +{ > + struct mem_cgroup *memcg = lruvec_memcg(lruvec); > + struct pglist_data *pgdat = lruvec_pgdat(lruvec); > + > + if (!can_demote(pgdat->node_id, sc) && > + mem_cgroup_get_nr_swap_pages(memcg) < MIN_LRU_BATCH) > + return 0; > + > + return mem_cgroup_swappiness(memcg); > +} > + > +static int get_nr_gens(struct lruvec *lruvec, int type) > +{ > + return lruvec->lrugen.max_seq - lruvec->lrugen.min_seq[type] + 1; > +} > + > +static bool __maybe_unused seq_is_valid(struct lruvec *lruvec) > +{ > + /* see the comment on lru_gen_struct */ > + return get_nr_gens(lruvec, LRU_GEN_FILE) >= MIN_NR_GENS && > + get_nr_gens(lruvec, LRU_GEN_FILE) <= get_nr_gens(lruvec, LRU_GEN_ANON) && > + get_nr_gens(lruvec, LRU_GEN_ANON) <= MAX_NR_GENS; > +} > + > +/****************************************************************************** > + * refault feedback loop > + ******************************************************************************/ > + > +/* > + * A feedback loop based on Proportional-Integral-Derivative (PID) controller. > + * > + * The P term is refaulted/(evicted+protected) from a tier in the generation > + * currently being evicted; the I term is the exponential moving average of the > + * P term over the generations previously evicted, using the smoothing factor > + * 1/2; the D term isn't supported. > + * > + * The setpoint (SP) is always the first tier of one type; the process variable > + * (PV) is either any tier of the other type or any other tier of the same > + * type. > + * > + * The error is the difference between the SP and the PV; the correction is > + * turn off protection when SP>PV or turn on protection when SP<PV. > + * > + * For future optimizations: > + * 1. The D term may discount the other two terms over time so that long-lived > + * generations can resist stale information. > + */ > +struct ctrl_pos { > + unsigned long refaulted; > + unsigned long total; > + int gain; > +}; > + > +static void read_ctrl_pos(struct lruvec *lruvec, int type, int tier, int gain, > + struct ctrl_pos *pos) > +{ > + struct lru_gen_struct *lrugen = &lruvec->lrugen; > + int hist = lru_hist_from_seq(lrugen->min_seq[type]); > + > + pos->refaulted = lrugen->avg_refaulted[type][tier] + > + atomic_long_read(&lrugen->refaulted[hist][type][tier]); > + pos->total = lrugen->avg_total[type][tier] + > + atomic_long_read(&lrugen->evicted[hist][type][tier]); > + if (tier) > + pos->total += lrugen->protected[hist][type][tier - 1]; > + pos->gain = gain; > +} > + > +static void reset_ctrl_pos(struct lruvec *lruvec, int type, bool carryover) > +{ > + int hist, tier; > + struct lru_gen_struct *lrugen = &lruvec->lrugen; > + bool clear = carryover ? NR_HIST_GENS == 1 : NR_HIST_GENS > 1; > + unsigned long seq = carryover ? lrugen->min_seq[type] : lrugen->max_seq + 1; > + > + lockdep_assert_held(&lruvec->lru_lock); > + > + if (!carryover && !clear) > + return; > + > + hist = lru_hist_from_seq(seq); > + > + for (tier = 0; tier < MAX_NR_TIERS; tier++) { > + if (carryover) { > + unsigned long sum; > + > + sum = lrugen->avg_refaulted[type][tier] + > + atomic_long_read(&lrugen->refaulted[hist][type][tier]); > + WRITE_ONCE(lrugen->avg_refaulted[type][tier], sum / 2); > + > + sum = lrugen->avg_total[type][tier] + > + atomic_long_read(&lrugen->evicted[hist][type][tier]); > + if (tier) > + sum += lrugen->protected[hist][type][tier - 1]; > + WRITE_ONCE(lrugen->avg_total[type][tier], sum / 2); > + } > + > + if (clear) { > + atomic_long_set(&lrugen->refaulted[hist][type][tier], 0); > + atomic_long_set(&lrugen->evicted[hist][type][tier], 0); > + if (tier) > + WRITE_ONCE(lrugen->protected[hist][type][tier - 1], 0); > + } > + } > +} > + > +static bool positive_ctrl_err(struct ctrl_pos *sp, struct ctrl_pos *pv) > +{ > + /* > + * Return true if the PV has a limited number of refaults or a lower > + * refaulted/total than the SP. > + */ > + return pv->refaulted < MIN_LRU_BATCH || > + pv->refaulted * (sp->total + MIN_LRU_BATCH) * sp->gain <= > + (sp->refaulted + 1) * pv->total * pv->gain; > +} > + > +/****************************************************************************** > + * the aging > + ******************************************************************************/ > + > +static int folio_inc_gen(struct lruvec *lruvec, struct folio *folio, bool reclaiming) > +{ > + unsigned long old_flags, new_flags; > + int type = folio_is_file_lru(folio); > + struct lru_gen_struct *lrugen = &lruvec->lrugen; > + int new_gen, old_gen = lru_gen_from_seq(lrugen->min_seq[type]); > + > + do { > + new_flags = old_flags = READ_ONCE(folio->flags); > + VM_BUG_ON_FOLIO(!(new_flags & LRU_GEN_MASK), folio); > + > + new_gen = (old_gen + 1) % MAX_NR_GENS; > + > + new_flags &= ~LRU_GEN_MASK; > + new_flags |= (new_gen + 1UL) << LRU_GEN_PGOFF; > + new_flags &= ~(LRU_REFS_MASK | LRU_REFS_FLAGS); > + /* for folio_end_writeback() */ > + if (reclaiming) > + new_flags |= BIT(PG_reclaim); > + } while (cmpxchg(&folio->flags, old_flags, new_flags) != old_flags); > + > + lru_gen_update_size(lruvec, folio, old_gen, new_gen); > + > + return new_gen; > +} > + > +static void inc_min_seq(struct lruvec *lruvec) > +{ > + int type; > + struct lru_gen_struct *lrugen = &lruvec->lrugen; > + > + VM_BUG_ON(!seq_is_valid(lruvec)); > + > + for (type = 0; type < ANON_AND_FILE; type++) { > + if (get_nr_gens(lruvec, type) != MAX_NR_GENS) > + continue; > + > + reset_ctrl_pos(lruvec, type, true); > + WRITE_ONCE(lrugen->min_seq[type], lrugen->min_seq[type] + 1); > + } > +} > + > +static bool try_to_inc_min_seq(struct lruvec *lruvec, bool can_swap) > +{ > + int gen, type, zone; > + bool success = false; > + struct lru_gen_struct *lrugen = &lruvec->lrugen; > + DEFINE_MIN_SEQ(lruvec); > + > + VM_BUG_ON(!seq_is_valid(lruvec)); > + > + for (type = !can_swap; type < ANON_AND_FILE; type++) { > + while (min_seq[type] + MIN_NR_GENS <= lrugen->max_seq) { > + gen = lru_gen_from_seq(min_seq[type]); > + > + for (zone = 0; zone < MAX_NR_ZONES; zone++) { > + if (!list_empty(&lrugen->lists[gen][type][zone])) > + goto next; > + } > + > + min_seq[type]++; > + } > +next: > + ; > + } > + > + /* see the comment on lru_gen_struct */ > + if (can_swap) { > + min_seq[LRU_GEN_ANON] = min(min_seq[LRU_GEN_ANON], min_seq[LRU_GEN_FILE]); > + min_seq[LRU_GEN_FILE] = max(min_seq[LRU_GEN_ANON], lrugen->min_seq[LRU_GEN_FILE]); > + } > + > + for (type = !can_swap; type < ANON_AND_FILE; type++) { > + if (min_seq[type] == lrugen->min_seq[type]) > + continue; > + > + reset_ctrl_pos(lruvec, type, true); > + WRITE_ONCE(lrugen->min_seq[type], min_seq[type]); > + success = true; > + } > + > + return success; > +} > + > +static void inc_max_seq(struct lruvec *lruvec, unsigned long max_seq) > +{ > + int prev, next; > + int type, zone; > + struct lru_gen_struct *lrugen = &lruvec->lrugen; > + > + spin_lock_irq(&lruvec->lru_lock); > + > + VM_BUG_ON(!seq_is_valid(lruvec)); > + > + if (max_seq != lrugen->max_seq) > + goto unlock; > + > + inc_min_seq(lruvec); > + > + /* > + * Update the active/inactive LRU sizes for compatibility. Both sides of > + * the current max_seq need to be covered, since max_seq+1 can overlap > + * with min_seq[LRU_GEN_ANON] if swapping is constrained. And if they do > + * overlap, cold/hot inversion happens. This can be solved by moving > + * pages from min_seq to min_seq+1 but is omitted for simplicity. > + */ > + prev = lru_gen_from_seq(lrugen->max_seq - 1); > + next = lru_gen_from_seq(lrugen->max_seq + 1); > + > + for (type = 0; type < ANON_AND_FILE; type++) { > + for (zone = 0; zone < MAX_NR_ZONES; zone++) { > + enum lru_list lru = type * LRU_INACTIVE_FILE; > + long delta = lrugen->nr_pages[prev][type][zone] - > + lrugen->nr_pages[next][type][zone]; > + > + if (!delta) > + continue; > + > + __update_lru_size(lruvec, lru, zone, delta); > + __update_lru_size(lruvec, lru + LRU_ACTIVE, zone, -delta); > + } > + } > + > + for (type = 0; type < ANON_AND_FILE; type++) > + reset_ctrl_pos(lruvec, type, false); > + > + /* make sure preceding modifications appear */ > + smp_store_release(&lrugen->max_seq, lrugen->max_seq + 1); > +unlock: > + spin_unlock_irq(&lruvec->lru_lock); > +} > + > +static long get_nr_evictable(struct lruvec *lruvec, unsigned long max_seq, > + unsigned long *min_seq, bool can_swap, bool *need_aging) > +{ > + int gen, type, zone; > + long old = 0; > + long young = 0; > + long total = 0; > + struct lru_gen_struct *lrugen = &lruvec->lrugen; > + > + for (type = !can_swap; type < ANON_AND_FILE; type++) { > + unsigned long seq; > + > + for (seq = min_seq[type]; seq <= max_seq; seq++) { > + long size = 0; > + > + gen = lru_gen_from_seq(seq); > + > + for (zone = 0; zone < MAX_NR_ZONES; zone++) > + size += READ_ONCE(lrugen->nr_pages[gen][type][zone]); > + > + total += size; > + if (seq == max_seq) > + young += size; > + if (seq + MIN_NR_GENS == max_seq) > + old += size; > + } > + } > + > + /* > + * The aging and the eviction is a typical producer-consumer model. The > + * aging tries to be lazy to reduce the unnecessary overhead. On the > + * other hand, the eviction stalls when the number of generations > + * reaches MIN_NR_GENS. So ideally, there should be MIN_NR_GENS+1 > + * generations, hence the first two if's. > + * > + * In addition, it's ideal to spread pages out evenly, meaning > + * 1/(MIN_NR_GENS+1) of the total number of pages for each generation. A > + * reasonable range for this average portion would [1/MIN_NR_GENS, > + * 1/(MIN_NR_GENS+2)]. From the consumer's POV, the eviction only cares > + * about the lower bound of cold pages, i.e., 1/(MIN_NR_GENS+2), whereas > + * from the producer's POV, the aging only cares about the upper bound > + * of hot pages, i.e., 1/MIN_NR_GENS. > + */ > + if (min_seq[LRU_GEN_FILE] + MIN_NR_GENS > max_seq) > + *need_aging = true; > + else if (min_seq[LRU_GEN_FILE] + MIN_NR_GENS < max_seq) > + *need_aging = false; > + else if (young * MIN_NR_GENS > total) > + *need_aging = true; > + else if (old * (MIN_NR_GENS + 2) < total) > + *need_aging = true; > + else > + *need_aging = false; > + > + return total > 0 ? total : 0; > +} > + > +static void age_lruvec(struct lruvec *lruvec, struct scan_control *sc) > +{ > + bool need_aging; > + long nr_to_scan; > + int swappiness = get_swappiness(lruvec, sc); > + struct mem_cgroup *memcg = lruvec_memcg(lruvec); > + DEFINE_MAX_SEQ(lruvec); > + DEFINE_MIN_SEQ(lruvec); > + > + mem_cgroup_calculate_protection(NULL, memcg); > + > + if (mem_cgroup_below_min(memcg)) > + return; > + > + nr_to_scan = get_nr_evictable(lruvec, max_seq, min_seq, swappiness, &need_aging); > + if (!nr_to_scan) > + return; > + > + nr_to_scan >>= sc->priority; > + > + if (!mem_cgroup_online(memcg)) > + nr_to_scan++; > + > + if (nr_to_scan && need_aging && (!mem_cgroup_below_low(memcg) || sc->memcg_low_reclaim)) > + inc_max_seq(lruvec, max_seq); > +} > + > +static void lru_gen_age_node(struct pglist_data *pgdat, struct scan_control *sc) > +{ > + struct mem_cgroup *memcg; > + > + VM_BUG_ON(!current_is_kswapd()); > + > + memcg = mem_cgroup_iter(NULL, NULL, NULL); > + do { > + struct lruvec *lruvec = mem_cgroup_lruvec(memcg, pgdat); > + > + age_lruvec(lruvec, sc); > + > + cond_resched(); > + } while ((memcg = mem_cgroup_iter(NULL, memcg, NULL))); > +} > + > +/****************************************************************************** > + * the eviction > + ******************************************************************************/ > + > +static bool sort_folio(struct lruvec *lruvec, struct folio *folio, int tier_idx) > +{ > + bool success; > + int gen = folio_lru_gen(folio); > + int type = folio_is_file_lru(folio); > + int zone = folio_zonenum(folio); > + int tier = folio_lru_tier(folio); > + int delta = folio_nr_pages(folio); > + struct lru_gen_struct *lrugen = &lruvec->lrugen; > + > + VM_BUG_ON_FOLIO(gen >= MAX_NR_GENS, folio); > + > + if (!folio_evictable(folio)) { > + success = lru_gen_del_folio(lruvec, folio, true); > + VM_BUG_ON_FOLIO(!success, folio); > + folio_set_unevictable(folio); > + lruvec_add_folio(lruvec, folio); > + __count_vm_events(UNEVICTABLE_PGCULLED, delta); > + return true; > + } > + > + if (type == LRU_GEN_FILE && folio_test_anon(folio) && folio_test_dirty(folio)) { > + success = lru_gen_del_folio(lruvec, folio, true); > + VM_BUG_ON_FOLIO(!success, folio); > + folio_set_swapbacked(folio); > + lruvec_add_folio_tail(lruvec, folio); > + return true; > + } > + > + if (tier > tier_idx) { > + int hist = lru_hist_from_seq(lrugen->min_seq[type]); > + > + gen = folio_inc_gen(lruvec, folio, false); > + list_move_tail(&folio->lru, &lrugen->lists[gen][type][zone]); > + > + WRITE_ONCE(lrugen->protected[hist][type][tier - 1], > + lrugen->protected[hist][type][tier - 1] + delta); > + __mod_lruvec_state(lruvec, WORKINGSET_ACTIVATE_BASE + type, delta); > + return true; > + } > + > + if (folio_test_locked(folio) || folio_test_writeback(folio) || > + (type == LRU_GEN_FILE && folio_test_dirty(folio))) { > + gen = folio_inc_gen(lruvec, folio, true); > + list_move(&folio->lru, &lrugen->lists[gen][type][zone]); > + return true; > + } > + > + return false; > +} > + > +static bool isolate_folio(struct lruvec *lruvec, struct folio *folio, struct scan_control *sc) > +{ > + bool success; > + > + if (!sc->may_unmap && folio_mapped(folio)) > + return false; > + > + if (!(sc->may_writepage && (sc->gfp_mask & __GFP_IO)) && > + (folio_test_dirty(folio) || > + (folio_test_anon(folio) && !folio_test_swapcache(folio)))) > + return false; > + > + if (!folio_try_get(folio)) > + return false; > + > + if (!folio_test_clear_lru(folio)) { > + folio_put(folio); > + return false; > + } > + > + success = lru_gen_del_folio(lruvec, folio, true); > + VM_BUG_ON_FOLIO(!success, folio); > + > + return true; > +} > + > +static int scan_folios(struct lruvec *lruvec, struct scan_control *sc, > + int type, int tier, struct list_head *list) > +{ > + int gen, zone; > + enum vm_event_item item; > + int sorted = 0; > + int scanned = 0; > + int isolated = 0; > + int remaining = MAX_LRU_BATCH; > + struct lru_gen_struct *lrugen = &lruvec->lrugen; > + struct mem_cgroup *memcg = lruvec_memcg(lruvec); > + > + VM_BUG_ON(!list_empty(list)); > + > + if (get_nr_gens(lruvec, type) == MIN_NR_GENS) > + return 0; > + > + gen = lru_gen_from_seq(lrugen->min_seq[type]); > + > + for (zone = sc->reclaim_idx; zone >= 0; zone--) { > + LIST_HEAD(moved); > + int skipped = 0; > + struct list_head *head = &lrugen->lists[gen][type][zone]; > + > + while (!list_empty(head)) { > + struct folio *folio = lru_to_folio(head); > + int delta = folio_nr_pages(folio); > + > + VM_BUG_ON_FOLIO(folio_test_unevictable(folio), folio); > + VM_BUG_ON_FOLIO(folio_test_active(folio), folio); > + VM_BUG_ON_FOLIO(folio_is_file_lru(folio) != type, folio); > + VM_BUG_ON_FOLIO(folio_zonenum(folio) != zone, folio); > + > + scanned += delta; > + > + if (sort_folio(lruvec, folio, tier)) > + sorted += delta; > + else if (isolate_folio(lruvec, folio, sc)) { > + list_add(&folio->lru, list); > + isolated += delta; > + } else { > + list_move(&folio->lru, &moved); > + skipped += delta; > + } > + > + if (!--remaining || max(isolated, skipped) >= MIN_LRU_BATCH) > + break; > + } > + > + if (skipped) { > + list_splice(&moved, head); > + __count_zid_vm_events(PGSCAN_SKIP, zone, skipped); > + } > + > + if (!remaining || isolated >= MIN_LRU_BATCH) > + break; > + } > + > + item = current_is_kswapd() ? PGSCAN_KSWAPD : PGSCAN_DIRECT; > + if (!cgroup_reclaim(sc)) { > + __count_vm_events(item, isolated); > + __count_vm_events(PGREFILL, sorted); > + } > + __count_memcg_events(memcg, item, isolated); > + __count_memcg_events(memcg, PGREFILL, sorted); > + __count_vm_events(PGSCAN_ANON + type, isolated); > + > + /* > + * There might not be eligible pages due to reclaim_idx, may_unmap and > + * may_writepage. Check the remaining to prevent livelock if there is no > + * progress. > + */ > + return isolated || !remaining ? scanned : 0; > +} > + > +static int get_tier_idx(struct lruvec *lruvec, int type) > +{ > + int tier; > + struct ctrl_pos sp, pv; > + > + /* > + * To leave a margin for fluctuations, use a larger gain factor (1:2). > + * This value is chosen because any other tier would have at least twice > + * as many refaults as the first tier. > + */ > + read_ctrl_pos(lruvec, type, 0, 1, &sp); > + for (tier = 1; tier < MAX_NR_TIERS; tier++) { > + read_ctrl_pos(lruvec, type, tier, 2, &pv); > + if (!positive_ctrl_err(&sp, &pv)) > + break; > + } > + > + return tier - 1; > +} > + > +static int get_type_to_scan(struct lruvec *lruvec, int swappiness, int *tier_idx) > +{ > + int type, tier; > + struct ctrl_pos sp, pv; > + int gain[ANON_AND_FILE] = { swappiness, 200 - swappiness }; > + > + /* > + * Compare the first tier of anon with that of file to determine which > + * type to scan. Also need to compare other tiers of the selected type > + * with the first tier of the other type to determine the last tier (of > + * the selected type) to evict. > + */ > + read_ctrl_pos(lruvec, LRU_GEN_ANON, 0, gain[LRU_GEN_ANON], &sp); > + read_ctrl_pos(lruvec, LRU_GEN_FILE, 0, gain[LRU_GEN_FILE], &pv); > + type = positive_ctrl_err(&sp, &pv); > + > + read_ctrl_pos(lruvec, !type, 0, gain[!type], &sp); > + for (tier = 1; tier < MAX_NR_TIERS; tier++) { > + read_ctrl_pos(lruvec, type, tier, gain[type], &pv); > + if (!positive_ctrl_err(&sp, &pv)) > + break; > + } > + > + *tier_idx = tier - 1; > + > + return type; > +} > + > +static int isolate_folios(struct lruvec *lruvec, struct scan_control *sc, int swappiness, > + int *type_scanned, struct list_head *list) > +{ > + int i; > + int type; > + int scanned; > + int tier = -1; > + DEFINE_MIN_SEQ(lruvec); > + > + VM_BUG_ON(!seq_is_valid(lruvec)); > + > + /* > + * Try to make the obvious choice first. When anon and file are both > + * available from the same generation, interpret swappiness 1 as file > + * first and 200 as anon first. > + */ Has this changed the ABI of swapiness? or it is only something meaningful for the internal code? if so, can we rename it to something else? otherwise, it is quite confusing. it seems 1 is set internally as a magic number here: +static void lru_gen_shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc) +{ + ... + else if (!cgroup_reclaim(sc) && get_swappiness(lruvec, sc)) + swappiness = 1; + else + swappiness = 0; + } obviously this swappiness is neither /proc/sys/vm/swappiness nor /sys/fs/cgroup/memory/<group>/>memory.swappiness, right? > + if (!swappiness) > + type = LRU_GEN_FILE; > + else if (min_seq[LRU_GEN_ANON] < min_seq[LRU_GEN_FILE]) > + type = LRU_GEN_ANON; > + else if (swappiness == 1) > + type = LRU_GEN_FILE; > + else if (swappiness == 200) > + type = LRU_GEN_ANON; > + else > + type = get_type_to_scan(lruvec, swappiness, &tier); > + > + for (i = !swappiness; i < ANON_AND_FILE; i++) { > + if (tier < 0) > + tier = get_tier_idx(lruvec, type); > + > + scanned = scan_folios(lruvec, sc, type, tier, list); > + if (scanned) > + break; > + > + type = !type; > + tier = -1; > + } > + > + *type_scanned = type; > + > + return scanned; > +} > + > +static int evict_folios(struct lruvec *lruvec, struct scan_control *sc, int swappiness) > +{ > + int type; > + int scanned; > + int reclaimed; > + LIST_HEAD(list); > + struct folio *folio; > + enum vm_event_item item; > + struct reclaim_stat stat; > + struct mem_cgroup *memcg = lruvec_memcg(lruvec); > + struct pglist_data *pgdat = lruvec_pgdat(lruvec); > + > + spin_lock_irq(&lruvec->lru_lock); > + > + scanned = isolate_folios(lruvec, sc, swappiness, &type, &list); > + > + if (try_to_inc_min_seq(lruvec, swappiness)) > + scanned++; > + > + if (get_nr_gens(lruvec, LRU_GEN_FILE) == MIN_NR_GENS) > + scanned = 0; > + > + spin_unlock_irq(&lruvec->lru_lock); > + > + if (list_empty(&list)) > + return scanned; > + > + reclaimed = shrink_page_list(&list, pgdat, sc, &stat, false); > + > + /* > + * To avoid livelock, don't add rejected pages back to the same lists > + * they were isolated from. See lru_gen_add_folio(). > + */ > + list_for_each_entry(folio, &list, lru) { > + folio_clear_referenced(folio); > + folio_clear_workingset(folio); > + > + if (folio_test_reclaim(folio) && > + (folio_test_dirty(folio) || folio_test_writeback(folio))) > + folio_clear_active(folio); > + else > + folio_set_active(folio); > + } > + > + spin_lock_irq(&lruvec->lru_lock); > + > + move_pages_to_lru(lruvec, &list); > + > + item = current_is_kswapd() ? PGSTEAL_KSWAPD : PGSTEAL_DIRECT; > + if (!cgroup_reclaim(sc)) > + __count_vm_events(item, reclaimed); > + __count_memcg_events(memcg, item, reclaimed); > + __count_vm_events(PGSTEAL_ANON + type, reclaimed); > + > + spin_unlock_irq(&lruvec->lru_lock); > + > + mem_cgroup_uncharge_list(&list); > + free_unref_page_list(&list); > + > + sc->nr_reclaimed += reclaimed; > + > + return scanned; > +} > + > +static long get_nr_to_scan(struct lruvec *lruvec, struct scan_control *sc, bool can_swap) > +{ > + bool need_aging; > + long nr_to_scan; > + struct mem_cgroup *memcg = lruvec_memcg(lruvec); > + DEFINE_MAX_SEQ(lruvec); > + DEFINE_MIN_SEQ(lruvec); > + > + if (mem_cgroup_below_min(memcg) || > + (mem_cgroup_below_low(memcg) && !sc->memcg_low_reclaim)) > + return 0; > + > + nr_to_scan = get_nr_evictable(lruvec, max_seq, min_seq, can_swap, &need_aging); > + if (!nr_to_scan) > + return 0; > + > + /* reset the priority if the target has been met */ > + nr_to_scan >>= sc->nr_reclaimed < sc->nr_to_reclaim ? sc->priority : DEF_PRIORITY; > + > + if (!mem_cgroup_online(memcg)) > + nr_to_scan++; > + > + if (!nr_to_scan) > + return 0; > + > + if (!need_aging) > + return nr_to_scan; > + > + /* leave the work to lru_gen_age_node() */ > + if (current_is_kswapd()) > + return 0; > + > + /* try other memcgs before going to the aging path */ > + if (!cgroup_reclaim(sc) && !sc->force_deactivate) { > + sc->skipped_deactivate = true; > + return 0; > + } > + > + inc_max_seq(lruvec, max_seq); > + > + return nr_to_scan; > +} > + > +static void lru_gen_shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc) > +{ > + struct blk_plug plug; > + long scanned = 0; > + > + lru_add_drain(); > + > + blk_start_plug(&plug); > + > + while (true) { () > + int delta; > + int swappiness; > + long nr_to_scan; > + > + if (sc->may_swap) > + swappiness = get_swappiness(lruvec, sc); > + else if (!cgroup_reclaim(sc) && get_swappiness(lruvec, sc)) > + swappiness = 1; > + else > + swappiness = 0; > + > + nr_to_scan = get_nr_to_scan(lruvec, sc, swappiness); > + if (!nr_to_scan) > + break; > + > + delta = evict_folios(lruvec, sc, swappiness); > + if (!delta) > + break; > + > + scanned += delta; > + if (scanned >= nr_to_scan) > + break; > + > + cond_resched(); > + } > + > + blk_finish_plug(&plug); > +} > + > /****************************************************************************** > * initialization > ******************************************************************************/ > @@ -3041,6 +3821,16 @@ static int __init init_lru_gen(void) > }; > late_initcall(init_lru_gen); > > +#else > + > +static void lru_gen_age_node(struct pglist_data *pgdat, struct scan_control *sc) > +{ > +} > + > +static void lru_gen_shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc) > +{ > +} > + > #endif /* CONFIG_LRU_GEN */ > > static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc) > @@ -3054,6 +3844,11 @@ static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc) > struct blk_plug plug; > bool scan_adjusted; > > + if (lru_gen_enabled()) { > + lru_gen_shrink_lruvec(lruvec, sc); > + return; > + } > + > get_scan_count(lruvec, sc, nr); > > /* Record the original scan target for proportional adjustments later */ > @@ -3558,6 +4353,9 @@ static void snapshot_refaults(struct mem_cgroup *target_memcg, pg_data_t *pgdat) > struct lruvec *target_lruvec; > unsigned long refaults; > > + if (lru_gen_enabled()) > + return; > + > target_lruvec = mem_cgroup_lruvec(target_memcg, pgdat); > refaults = lruvec_page_state(target_lruvec, WORKINGSET_ACTIVATE_ANON); > target_lruvec->refaults[0] = refaults; > @@ -3928,6 +4726,11 @@ static void age_active_anon(struct pglist_data *pgdat, > struct mem_cgroup *memcg; > struct lruvec *lruvec; > > + if (lru_gen_enabled()) { > + lru_gen_age_node(pgdat, sc); > + return; > + } is it really a good place for lru_gen_age_node() since the function is named age_active_anon() but here you are doing aging for both anon and file pages? obviously lru_gen_age_node() is not doing "age active anon". > + > if (!can_age_anon_pages(pgdat, sc)) > return; > > diff --git a/mm/workingset.c b/mm/workingset.c > index 8a3828acc0bf..89b46af74eef 100644 > --- a/mm/workingset.c > +++ b/mm/workingset.c > @@ -187,7 +187,6 @@ static unsigned int bucket_order __read_mostly; > static void *pack_shadow(int memcgid, pg_data_t *pgdat, unsigned long eviction, > bool workingset) > { > - eviction >>= bucket_order; > eviction &= EVICTION_MASK; > eviction = (eviction << MEM_CGROUP_ID_SHIFT) | memcgid; > eviction = (eviction << NODES_SHIFT) | pgdat->node_id; > @@ -212,10 +211,116 @@ static void unpack_shadow(void *shadow, int *memcgidp, pg_data_t **pgdat, > > *memcgidp = memcgid; > *pgdat = NODE_DATA(nid); > - *evictionp = entry << bucket_order; > + *evictionp = entry; > *workingsetp = workingset; > } > > +#ifdef CONFIG_LRU_GEN > + > +static int folio_lru_refs(struct folio *folio) > +{ > + unsigned long flags = READ_ONCE(folio->flags); > + > + BUILD_BUG_ON(LRU_GEN_WIDTH + LRU_REFS_WIDTH > BITS_PER_LONG - EVICTION_SHIFT); > + > + /* see the comment on MAX_NR_TIERS */ > + return flags & BIT(PG_workingset) ? (flags & LRU_REFS_MASK) >> LRU_REFS_PGOFF : 0; > +} > + > +static void *lru_gen_eviction(struct folio *folio) > +{ > + int hist, tier; > + unsigned long token; > + unsigned long min_seq; > + struct lruvec *lruvec; > + struct lru_gen_struct *lrugen; > + int type = folio_is_file_lru(folio); > + int refs = folio_lru_refs(folio); > + int delta = folio_nr_pages(folio); > + bool workingset = folio_test_workingset(folio); > + struct mem_cgroup *memcg = folio_memcg(folio); > + struct pglist_data *pgdat = folio_pgdat(folio); > + > + lruvec = mem_cgroup_lruvec(memcg, pgdat); > + lrugen = &lruvec->lrugen; > + min_seq = READ_ONCE(lrugen->min_seq[type]); > + token = (min_seq << LRU_REFS_WIDTH) | refs; > + > + hist = lru_hist_from_seq(min_seq); > + tier = lru_tier_from_refs(refs + workingset); > + atomic_long_add(delta, &lrugen->evicted[hist][type][tier]); > + > + return pack_shadow(mem_cgroup_id(memcg), pgdat, token, workingset); > +} > + > +static void lru_gen_refault(struct folio *folio, void *shadow) > +{ > + int hist, tier, refs; > + int memcg_id; > + bool workingset; > + unsigned long token; > + unsigned long min_seq; > + struct lruvec *lruvec; > + struct lru_gen_struct *lrugen; > + struct mem_cgroup *memcg; > + struct pglist_data *pgdat; > + int type = folio_is_file_lru(folio); > + int delta = folio_nr_pages(folio); > + > + unpack_shadow(shadow, &memcg_id, &pgdat, &token, &workingset); > + > + refs = token & (BIT(LRU_REFS_WIDTH) - 1); > + if (refs && !workingset) > + return; > + > + if (folio_pgdat(folio) != pgdat) > + return; > + > + rcu_read_lock(); > + memcg = folio_memcg_rcu(folio); > + if (mem_cgroup_id(memcg) != memcg_id) > + goto unlock; > + > + token >>= LRU_REFS_WIDTH; > + lruvec = mem_cgroup_lruvec(memcg, pgdat); > + lrugen = &lruvec->lrugen; > + min_seq = READ_ONCE(lrugen->min_seq[type]); > + if (token != (min_seq & (EVICTION_MASK >> LRU_REFS_WIDTH))) > + goto unlock; > + > + hist = lru_hist_from_seq(min_seq); > + tier = lru_tier_from_refs(refs + workingset); > + atomic_long_add(delta, &lrugen->refaulted[hist][type][tier]); > + mod_lruvec_state(lruvec, WORKINGSET_REFAULT_BASE + type, delta); > + > + /* > + * Count the following two cases as stalls: > + * 1. For pages accessed through page tables, hotter pages pushed out > + * hot pages which refaulted immediately. > + * 2. For pages accessed through file descriptors, numbers of accesses > + * might have been beyond the limit. > + */ > + if (lru_gen_in_fault() || refs + workingset == BIT(LRU_REFS_WIDTH)) { > + folio_set_workingset(folio); > + mod_lruvec_state(lruvec, WORKINGSET_RESTORE_BASE + type, delta); > + } > +unlock: > + rcu_read_unlock(); > +} > + > +#else > + > +static void *lru_gen_eviction(struct folio *folio) > +{ > + return NULL; > +} > + > +static void lru_gen_refault(struct folio *folio, void *shadow) > +{ > +} > + > +#endif /* CONFIG_LRU_GEN */ > + > /** > * workingset_age_nonresident - age non-resident entries as LRU ages > * @lruvec: the lruvec that was aged > @@ -264,10 +369,14 @@ void *workingset_eviction(struct folio *folio, struct mem_cgroup *target_memcg) > VM_BUG_ON_FOLIO(folio_ref_count(folio), folio); > VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio); > > + if (lru_gen_enabled()) > + return lru_gen_eviction(folio); > + > lruvec = mem_cgroup_lruvec(target_memcg, pgdat); > /* XXX: target_memcg can be NULL, go through lruvec */ > memcgid = mem_cgroup_id(lruvec_memcg(lruvec)); > eviction = atomic_long_read(&lruvec->nonresident_age); > + eviction >>= bucket_order; > workingset_age_nonresident(lruvec, folio_nr_pages(folio)); > return pack_shadow(memcgid, pgdat, eviction, > folio_test_workingset(folio)); > @@ -298,7 +407,13 @@ void workingset_refault(struct folio *folio, void *shadow) > int memcgid; > long nr; > > + if (lru_gen_enabled()) { > + lru_gen_refault(folio, shadow); > + return; > + } > + > unpack_shadow(shadow, &memcgid, &pgdat, &eviction, &workingset); > + eviction <<= bucket_order; > > rcu_read_lock(); > /* > -- > 2.35.1.1094.g7c7d902a7c-goog > Thanks Barry
On 2022/4/7 11:15, Yu Zhao wrote: > To avoid confusion, the terms "promotion" and "demotion" will be > applied to the multi-gen LRU, as a new convention; the terms > "activation" and "deactivation" will be applied to the active/inactive > LRU, as usual. > > The aging produces young generations. Given an lruvec, it increments > max_seq when max_seq-min_seq+1 approaches MIN_NR_GENS. The aging > promotes hot pages to the youngest generation when it finds them > accessed through page tables; the demotion of cold pages happens > consequently when it increments max_seq. The aging has the complexity > O(nr_hot_pages), since it is only interested in hot pages. Promotion > in the aging path does not require any LRU list operations, only the > updates of the gen counter and lrugen->nr_pages[]; demotion, unless as > the result of the increment of max_seq, requires LRU list operations, > e.g., lru_deactivate_fn(). > > The eviction consumes old generations. Given an lruvec, it increments > min_seq when the lists indexed by min_seq%MAX_NR_GENS become empty. A > feedback loop modeled after the PID controller monitors refaults over > anon and file types and decides which type to evict when both types > are available from the same generation. > > Each generation is divided into multiple tiers. Tiers represent > different ranges of numbers of accesses through file descriptors. A > page accessed N times through file descriptors is in tier > order_base_2(N). Tiers do not have dedicated lrugen->lists[], only > bits in folio->flags. In contrast to moving across generations, which > requires the LRU lock, moving across tiers only involves operations on > folio->flags. The feedback loop also monitors refaults over all tiers > and decides when to protect pages in which tiers (N>1), using the > first tier (N=0,1) as a baseline. The first tier contains single-use > unmapped clean pages, which are most likely the best choices. The > eviction moves a page to the next generation, i.e., min_seq+1, if the > feedback loop decides so. This approach has the following advantages: > 1. It removes the cost of activation in the buffered access path by > inferring whether pages accessed multiple times through file > descriptors are statistically hot and thus worth protecting in the > eviction path. > 2. It takes pages accessed through page tables into account and avoids > overprotecting pages accessed multiple times through file > descriptors. (Pages accessed through page tables are in the first > tier, since N=0.) > 3. More tiers provide better protection for pages accessed more than > twice through file descriptors, when under heavy buffered I/O > workloads. > > Server benchmark results: > Single workload: > fio (buffered I/O): +[40, 42]% > IOPS BW > 5.18-rc1: 2463k 9621MiB/s > patch1-6: 3484k 13.3GiB/s > > Single workload: > memcached (anon): +[44, 46]% > Ops/sec KB/sec > 5.18-rc1: 771403.27 30004.17 > patch1-6: 1120643.70 43588.06 > > Configurations: > CPU: two Xeon 6154 > Mem: total 256G > > Node 1 was only used as a ram disk to reduce the variance in the > results. > > patch drivers/block/brd.c <<EOF > 99,100c99,100 > < gfp_flags = GFP_NOIO | __GFP_ZERO | __GFP_HIGHMEM; > < page = alloc_page(gfp_flags); > --- > > gfp_flags = GFP_NOIO | __GFP_ZERO | __GFP_HIGHMEM | __GFP_THISNODE; > > page = alloc_pages_node(1, gfp_flags, 0); > EOF > > cat >>/etc/systemd/system.conf <<EOF > CPUAffinity=numa > NUMAPolicy=bind > NUMAMask=0 > EOF > > cat >>/etc/memcached.conf <<EOF > -m 184320 > -s /var/run/memcached/memcached.sock > -a 0766 > -t 36 > -B binary > EOF > > cat fio.sh > modprobe brd rd_nr=1 rd_size=113246208 > swapoff -a > mkfs.ext4 /dev/ram0 > mount -t ext4 /dev/ram0 /mnt > > mkdir /sys/fs/cgroup/user.slice/test > echo 38654705664 >/sys/fs/cgroup/user.slice/test/memory.max > echo $$ >/sys/fs/cgroup/user.slice/test/cgroup.procs > fio -name=mglru --numjobs=72 --directory=/mnt --size=1408m \ > --buffered=1 --ioengine=io_uring --iodepth=128 \ > --iodepth_batch_submit=32 --iodepth_batch_complete=32 \ > --rw=randread --random_distribution=random --norandommap \ > --time_based --ramp_time=10m --runtime=5m --group_reporting > > cat memcached.sh > modprobe brd rd_nr=1 rd_size=113246208 > swapoff -a > mkswap /dev/ram0 > swapon /dev/ram0 > > memtier_benchmark -S /var/run/memcached/memcached.sock \ > -P memcache_binary -n allkeys --key-minimum=1 \ > --key-maximum=65000000 --key-pattern=P:P -c 1 -t 36 \ > --ratio 1:0 --pipeline 8 -d 2000 > > memtier_benchmark -S /var/run/memcached/memcached.sock \ > -P memcache_binary -n allkeys --key-minimum=1 \ > --key-maximum=65000000 --key-pattern=R:R -c 1 -t 36 \ > --ratio 0:1 --pipeline 8 --randomize --distinct-client-seed > > Client benchmark results: > kswapd profiles: > 5.18-rc1 > 40.53% page_vma_mapped_walk > 20.37% lzo1x_1_do_compress (real work) > 6.99% do_raw_spin_lock > 3.93% _raw_spin_unlock_irq > 2.08% vma_interval_tree_subtree_search > 2.06% vma_interval_tree_iter_next > 1.95% folio_referenced_one > 1.93% anon_vma_interval_tree_iter_first > 1.51% ptep_clear_flush > 1.35% __anon_vma_interval_tree_subtree_search > > patch1-6 > 35.99% lzo1x_1_do_compress (real work) > 19.40% page_vma_mapped_walk > 6.31% _raw_spin_unlock_irq > 3.95% do_raw_spin_lock > 2.39% anon_vma_interval_tree_iter_first > 2.25% ptep_clear_flush > 1.92% __anon_vma_interval_tree_subtree_search > 1.70% folio_referenced_one > 1.68% __zram_bvec_write > 1.43% anon_vma_interval_tree_iter_next > > Configurations: > CPU: single Snapdragon 7c > Mem: total 4G > > Chrome OS MemoryPressure [1] > > [1] https://chromium.googlesource.com/chromiumos/platform/tast-tests/ > > Signed-off-by: Yu Zhao <yuzhao@google.com> > Acked-by: Brian Geffon <bgeffon@google.com> > Acked-by: Jan Alexander Steffens (heftig) <heftig@archlinux.org> > Acked-by: Oleksandr Natalenko <oleksandr@natalenko.name> > Acked-by: Steven Barrett <steven@liquorix.net> > Acked-by: Suleiman Souhlal <suleiman@google.com> > Tested-by: Daniel Byrne <djbyrne@mtu.edu> > Tested-by: Donald Carr <d@chaos-reins.com> > Tested-by: Holger Hoffstätte <holger@applied-asynchrony.com> > Tested-by: Konstantin Kharlamov <Hi-Angel@yandex.ru> > Tested-by: Shuang Zhai <szhai2@cs.rochester.edu> > Tested-by: Sofia Trinh <sofia.trinh@edi.works> > Tested-by: Vaibhav Jain <vaibhav@linux.ibm.com> > --- > include/linux/mm_inline.h | 24 ++ > include/linux/mmzone.h | 41 ++ > kernel/bounds.c | 2 +- > mm/Kconfig | 11 + > mm/swap.c | 42 ++ > mm/vmscan.c | 805 +++++++++++++++++++++++++++++++++++++- > mm/workingset.c | 119 +++++- > 7 files changed, 1040 insertions(+), 4 deletions(-) > > diff --git a/include/linux/mm_inline.h b/include/linux/mm_inline.h > index 9abd72a95462..8a8f87b72540 100644 > --- a/include/linux/mm_inline.h > +++ b/include/linux/mm_inline.h > @@ -119,6 +119,19 @@ static inline int lru_gen_from_seq(unsigned long seq) > return seq % MAX_NR_GENS; > } > > +static inline int lru_hist_from_seq(unsigned long seq) > +{ > + return seq % NR_HIST_GENS; > +} > + > +static inline int lru_tier_from_refs(int refs) > +{ > + VM_BUG_ON(refs > BIT(LRU_REFS_WIDTH)); > + > + /* see the comment on MAX_NR_TIERS */ > + return order_base_2(refs + 1); > +} > + > static inline bool lru_gen_is_active(struct lruvec *lruvec, int gen) > { > unsigned long max_seq = lruvec->lrugen.max_seq; > @@ -164,6 +177,15 @@ static inline void lru_gen_update_size(struct lruvec *lruvec, struct folio *foli > __update_lru_size(lruvec, lru, zone, -delta); > return; > } > + > + /* promotion */ > + if (!lru_gen_is_active(lruvec, old_gen) && lru_gen_is_active(lruvec, new_gen)) { > + __update_lru_size(lruvec, lru, zone, -delta); > + __update_lru_size(lruvec, lru + LRU_ACTIVE, zone, delta); > + } > + > + /* demotion requires isolation, e.g., lru_deactivate_fn() */ > + VM_BUG_ON(lru_gen_is_active(lruvec, old_gen) && !lru_gen_is_active(lruvec, new_gen)); > } > > static inline bool lru_gen_add_folio(struct lruvec *lruvec, struct folio *folio, bool reclaiming) > @@ -229,6 +251,8 @@ static inline bool lru_gen_del_folio(struct lruvec *lruvec, struct folio *folio, > gen = ((new_flags & LRU_GEN_MASK) >> LRU_GEN_PGOFF) - 1; > > new_flags &= ~LRU_GEN_MASK; > + if (!(new_flags & BIT(PG_referenced))) > + new_flags &= ~(LRU_REFS_MASK | LRU_REFS_FLAGS); > /* for shrink_page_list() */ > if (reclaiming) > new_flags &= ~(BIT(PG_referenced) | BIT(PG_reclaim)); > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h > index bde05427e2bb..c8a7ceee7a0a 100644 > --- a/include/linux/mmzone.h > +++ b/include/linux/mmzone.h > @@ -347,12 +347,34 @@ enum lruvec_flags { > #define MIN_NR_GENS 2U > #define MAX_NR_GENS 4U > > +/* > + * Each generation is divided into multiple tiers. Tiers represent different > + * ranges of numbers of accesses through file descriptors. A page accessed N > + * times through file descriptors is in tier order_base_2(N). A page in the > + * first tier (N=0,1) is marked by PG_referenced unless it was faulted in > + * though page tables or read ahead. A page in any other tier (N>1) is marked > + * by PG_referenced and PG_workingset. > + * > + * In contrast to moving across generations which requires the LRU lock, moving > + * across tiers only requires operations on folio->flags and therefore has a > + * negligible cost in the buffered access path. In the eviction path, > + * comparisons of refaulted/(evicted+protected) from the first tier and the > + * rest infer whether pages accessed multiple times through file descriptors > + * are statistically hot and thus worth protecting. > + * > + * MAX_NR_TIERS is set to 4 so that the multi-gen LRU can support twice of the > + * categories of the active/inactive LRU when keeping track of accesses through > + * file descriptors. It requires MAX_NR_TIERS-2 additional bits in folio->flags. > + */ > +#define MAX_NR_TIERS 4U > + > #ifndef __GENERATING_BOUNDS_H > > struct lruvec; > > #define LRU_GEN_MASK ((BIT(LRU_GEN_WIDTH) - 1) << LRU_GEN_PGOFF) > #define LRU_REFS_MASK ((BIT(LRU_REFS_WIDTH) - 1) << LRU_REFS_PGOFF) > +#define LRU_REFS_FLAGS (BIT(PG_referenced) | BIT(PG_workingset)) > > #ifdef CONFIG_LRU_GEN > > @@ -361,6 +383,16 @@ enum { > LRU_GEN_FILE, > }; > > +#define MIN_LRU_BATCH BITS_PER_LONG > +#define MAX_LRU_BATCH (MIN_LRU_BATCH * 128) > + > +/* whether to keep historical stats from evicted generations */ > +#ifdef CONFIG_LRU_GEN_STATS > +#define NR_HIST_GENS MAX_NR_GENS > +#else > +#define NR_HIST_GENS 1U > +#endif > + > /* > * The youngest generation number is stored in max_seq for both anon and file > * types as they are aged on an equal footing. The oldest generation numbers are > @@ -380,6 +412,15 @@ struct lru_gen_struct { > struct list_head lists[MAX_NR_GENS][ANON_AND_FILE][MAX_NR_ZONES]; > /* the sizes of the above lists */ > unsigned long nr_pages[MAX_NR_GENS][ANON_AND_FILE][MAX_NR_ZONES]; > + /* the exponential moving average of refaulted */ > + unsigned long avg_refaulted[ANON_AND_FILE][MAX_NR_TIERS]; > + /* the exponential moving average of evicted+protected */ > + unsigned long avg_total[ANON_AND_FILE][MAX_NR_TIERS]; > + /* the first tier doesn't need protection, hence the minus one */ > + unsigned long protected[NR_HIST_GENS][ANON_AND_FILE][MAX_NR_TIERS - 1]; > + /* can be modified without holding the LRU lock */ > + atomic_long_t evicted[NR_HIST_GENS][ANON_AND_FILE][MAX_NR_TIERS]; > + atomic_long_t refaulted[NR_HIST_GENS][ANON_AND_FILE][MAX_NR_TIERS]; > }; > > void lru_gen_init_lruvec(struct lruvec *lruvec); > diff --git a/kernel/bounds.c b/kernel/bounds.c > index e08fb89f87f4..10dd9e6b03e5 100644 > --- a/kernel/bounds.c > +++ b/kernel/bounds.c > @@ -24,7 +24,7 @@ int main(void) > DEFINE(SPINLOCK_SIZE, sizeof(spinlock_t)); > #ifdef CONFIG_LRU_GEN > DEFINE(LRU_GEN_WIDTH, order_base_2(MAX_NR_GENS + 1)); > - DEFINE(LRU_REFS_WIDTH, 0); > + DEFINE(LRU_REFS_WIDTH, MAX_NR_TIERS - 2); > #else > DEFINE(LRU_GEN_WIDTH, 0); > DEFINE(LRU_REFS_WIDTH, 0); > diff --git a/mm/Kconfig b/mm/Kconfig > index 4595fc654181..c40777d098a8 100644 > --- a/mm/Kconfig > +++ b/mm/Kconfig > @@ -909,6 +909,7 @@ config ANON_VMA_NAME > area from being merged with adjacent virtual memory areas due to the > difference in their name. > > +# multi-gen LRU { > config LRU_GEN > bool "Multi-Gen LRU" > depends on MMU > @@ -917,6 +918,16 @@ config LRU_GEN > help > A high performance LRU implementation to overcommit memory. > > +config LRU_GEN_STATS > + bool "Full stats for debugging" > + depends on LRU_GEN > + help > + Do not enable this option unless you plan to look at historical stats > + from evicted generations for debugging purpose. > + > + This option has a per-memcg and per-node memory overhead. > +# } > + > source "mm/damon/Kconfig" > > endmenu > diff --git a/mm/swap.c b/mm/swap.c > index a6870ba0bd83..6a5203f18b0a 100644 > --- a/mm/swap.c > +++ b/mm/swap.c > @@ -405,6 +405,43 @@ static void __lru_cache_activate_folio(struct folio *folio) > local_unlock(&lru_pvecs.lock); > } > > +#ifdef CONFIG_LRU_GEN > +static void folio_inc_refs(struct folio *folio) > +{ > + unsigned long refs; > + unsigned long old_flags, new_flags; > + > + if (folio_test_unevictable(folio)) > + return; > + > + /* see the comment on MAX_NR_TIERS */ > + do { > + new_flags = old_flags = READ_ONCE(folio->flags); > + > + if (!(new_flags & BIT(PG_referenced))) { > + new_flags |= BIT(PG_referenced); > + continue; > + } > + > + if (!(new_flags & BIT(PG_workingset))) { > + new_flags |= BIT(PG_workingset); > + continue; > + } > + > + refs = new_flags & LRU_REFS_MASK; > + refs = min(refs + BIT(LRU_REFS_PGOFF), LRU_REFS_MASK); > + > + new_flags &= ~LRU_REFS_MASK; > + new_flags |= refs; > + } while (new_flags != old_flags && > + cmpxchg(&folio->flags, old_flags, new_flags) != old_flags); > +} > +#else > +static void folio_inc_refs(struct folio *folio) > +{ > +} > +#endif /* CONFIG_LRU_GEN */ > + > /* > * Mark a page as having seen activity. > * > @@ -417,6 +454,11 @@ static void __lru_cache_activate_folio(struct folio *folio) > */ > void folio_mark_accessed(struct folio *folio) > { > + if (lru_gen_enabled()) { > + folio_inc_refs(folio); > + return; > + } > + > if (!folio_test_referenced(folio)) { > folio_set_referenced(folio); > } else if (folio_test_unevictable(folio)) { > diff --git a/mm/vmscan.c b/mm/vmscan.c > index 37dd5d1c3d07..bb3d705c5282 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -1275,9 +1275,11 @@ static int __remove_mapping(struct address_space *mapping, struct folio *folio, > > if (folio_test_swapcache(folio)) { > swp_entry_t swap = folio_swap_entry(folio); > - mem_cgroup_swapout(folio, swap); > + > + /* get a shadow entry before mem_cgroup_swapout() clears folio_memcg() */ > if (reclaimed && !mapping_exiting(mapping)) > shadow = workingset_eviction(folio, target_memcg); > + mem_cgroup_swapout(folio, swap); > __delete_from_swap_cache(&folio->page, swap, shadow); > xa_unlock_irq(&mapping->i_pages); > put_swap_page(&folio->page, swap); > @@ -2649,6 +2651,9 @@ static void prepare_scan_count(pg_data_t *pgdat, struct scan_control *sc) > unsigned long file; > struct lruvec *target_lruvec; > > + if (lru_gen_enabled()) > + return; > + > target_lruvec = mem_cgroup_lruvec(sc->target_mem_cgroup, pgdat); > > /* > @@ -2974,11 +2979,38 @@ static bool can_age_anon_pages(struct pglist_data *pgdat, > * shorthand helpers > ******************************************************************************/ > > +#define DEFINE_MAX_SEQ(lruvec) \ > + unsigned long max_seq = READ_ONCE((lruvec)->lrugen.max_seq) > + > +#define DEFINE_MIN_SEQ(lruvec) \ > + unsigned long min_seq[ANON_AND_FILE] = { \ > + READ_ONCE((lruvec)->lrugen.min_seq[LRU_GEN_ANON]), \ > + READ_ONCE((lruvec)->lrugen.min_seq[LRU_GEN_FILE]), \ > + } > + > #define for_each_gen_type_zone(gen, type, zone) \ > for ((gen) = 0; (gen) < MAX_NR_GENS; (gen)++) \ > for ((type) = 0; (type) < ANON_AND_FILE; (type)++) \ > for ((zone) = 0; (zone) < MAX_NR_ZONES; (zone)++) > > +static int folio_lru_gen(struct folio *folio) > +{ > + unsigned long flags = READ_ONCE(folio->flags); > + > + return ((flags & LRU_GEN_MASK) >> LRU_GEN_PGOFF) - 1; > +} > + > +static int folio_lru_tier(struct folio *folio) > +{ > + int refs; > + unsigned long flags = READ_ONCE(folio->flags); > + > + refs = (flags & LRU_REFS_FLAGS) == LRU_REFS_FLAGS ? > + ((flags & LRU_REFS_MASK) >> LRU_REFS_PGOFF) + 1 : 0; > + > + return lru_tier_from_refs(refs); > +} > + > static struct lruvec __maybe_unused *get_lruvec(struct mem_cgroup *memcg, int nid) > { > struct pglist_data *pgdat = NODE_DATA(nid); > @@ -2999,6 +3031,754 @@ static struct lruvec __maybe_unused *get_lruvec(struct mem_cgroup *memcg, int ni > return pgdat ? &pgdat->__lruvec : NULL; > } > > +static int get_swappiness(struct lruvec *lruvec, struct scan_control *sc) > +{ > + struct mem_cgroup *memcg = lruvec_memcg(lruvec); > + struct pglist_data *pgdat = lruvec_pgdat(lruvec); > + > + if (!can_demote(pgdat->node_id, sc) && > + mem_cgroup_get_nr_swap_pages(memcg) < MIN_LRU_BATCH) > + return 0; > + > + return mem_cgroup_swappiness(memcg); > +} > + > +static int get_nr_gens(struct lruvec *lruvec, int type) > +{ > + return lruvec->lrugen.max_seq - lruvec->lrugen.min_seq[type] + 1; > +} > + > +static bool __maybe_unused seq_is_valid(struct lruvec *lruvec) > +{ > + /* see the comment on lru_gen_struct */ > + return get_nr_gens(lruvec, LRU_GEN_FILE) >= MIN_NR_GENS && > + get_nr_gens(lruvec, LRU_GEN_FILE) <= get_nr_gens(lruvec, LRU_GEN_ANON) && > + get_nr_gens(lruvec, LRU_GEN_ANON) <= MAX_NR_GENS; > +} > + > +/****************************************************************************** > + * refault feedback loop > + ******************************************************************************/ > + > +/* > + * A feedback loop based on Proportional-Integral-Derivative (PID) controller. > + * > + * The P term is refaulted/(evicted+protected) from a tier in the generation > + * currently being evicted; the I term is the exponential moving average of the > + * P term over the generations previously evicted, using the smoothing factor > + * 1/2; the D term isn't supported. > + * > + * The setpoint (SP) is always the first tier of one type; the process variable > + * (PV) is either any tier of the other type or any other tier of the same > + * type. > + * > + * The error is the difference between the SP and the PV; the correction is > + * turn off protection when SP>PV or turn on protection when SP<PV. > + * > + * For future optimizations: > + * 1. The D term may discount the other two terms over time so that long-lived > + * generations can resist stale information. > + */ > +struct ctrl_pos { > + unsigned long refaulted; > + unsigned long total; > + int gain; > +}; > + > +static void read_ctrl_pos(struct lruvec *lruvec, int type, int tier, int gain, > + struct ctrl_pos *pos) > +{ > + struct lru_gen_struct *lrugen = &lruvec->lrugen; > + int hist = lru_hist_from_seq(lrugen->min_seq[type]); > + > + pos->refaulted = lrugen->avg_refaulted[type][tier] + > + atomic_long_read(&lrugen->refaulted[hist][type][tier]); > + pos->total = lrugen->avg_total[type][tier] + > + atomic_long_read(&lrugen->evicted[hist][type][tier]); > + if (tier) > + pos->total += lrugen->protected[hist][type][tier - 1]; > + pos->gain = gain; > +} > + > +static void reset_ctrl_pos(struct lruvec *lruvec, int type, bool carryover) > +{ > + int hist, tier; > + struct lru_gen_struct *lrugen = &lruvec->lrugen; > + bool clear = carryover ? NR_HIST_GENS == 1 : NR_HIST_GENS > 1; > + unsigned long seq = carryover ? lrugen->min_seq[type] : lrugen->max_seq + 1; > + > + lockdep_assert_held(&lruvec->lru_lock); > + > + if (!carryover && !clear) > + return; > + > + hist = lru_hist_from_seq(seq); > + > + for (tier = 0; tier < MAX_NR_TIERS; tier++) { > + if (carryover) { > + unsigned long sum; > + > + sum = lrugen->avg_refaulted[type][tier] + > + atomic_long_read(&lrugen->refaulted[hist][type][tier]); > + WRITE_ONCE(lrugen->avg_refaulted[type][tier], sum / 2); > + > + sum = lrugen->avg_total[type][tier] + > + atomic_long_read(&lrugen->evicted[hist][type][tier]); > + if (tier) > + sum += lrugen->protected[hist][type][tier - 1]; > + WRITE_ONCE(lrugen->avg_total[type][tier], sum / 2); > + } > + > + if (clear) { > + atomic_long_set(&lrugen->refaulted[hist][type][tier], 0); > + atomic_long_set(&lrugen->evicted[hist][type][tier], 0); > + if (tier) > + WRITE_ONCE(lrugen->protected[hist][type][tier - 1], 0); > + } > + } > +} > + > +static bool positive_ctrl_err(struct ctrl_pos *sp, struct ctrl_pos *pv) > +{ > + /* > + * Return true if the PV has a limited number of refaults or a lower > + * refaulted/total than the SP. > + */ > + return pv->refaulted < MIN_LRU_BATCH || > + pv->refaulted * (sp->total + MIN_LRU_BATCH) * sp->gain <= > + (sp->refaulted + 1) * pv->total * pv->gain; > +} > + > +/****************************************************************************** > + * the aging > + ******************************************************************************/ > + > +static int folio_inc_gen(struct lruvec *lruvec, struct folio *folio, bool reclaiming) > +{ > + unsigned long old_flags, new_flags; > + int type = folio_is_file_lru(folio); > + struct lru_gen_struct *lrugen = &lruvec->lrugen; > + int new_gen, old_gen = lru_gen_from_seq(lrugen->min_seq[type]); > + > + do { > + new_flags = old_flags = READ_ONCE(folio->flags); > + VM_BUG_ON_FOLIO(!(new_flags & LRU_GEN_MASK), folio); > + > + new_gen = (old_gen + 1) % MAX_NR_GENS; > + > + new_flags &= ~LRU_GEN_MASK; > + new_flags |= (new_gen + 1UL) << LRU_GEN_PGOFF; > + new_flags &= ~(LRU_REFS_MASK | LRU_REFS_FLAGS); > + /* for folio_end_writeback() */ > + if (reclaiming) > + new_flags |= BIT(PG_reclaim); > + } while (cmpxchg(&folio->flags, old_flags, new_flags) != old_flags); > + > + lru_gen_update_size(lruvec, folio, old_gen, new_gen); > + > + return new_gen; > +} > + > +static void inc_min_seq(struct lruvec *lruvec) > +{ > + int type; > + struct lru_gen_struct *lrugen = &lruvec->lrugen; > + > + VM_BUG_ON(!seq_is_valid(lruvec)); > + > + for (type = 0; type < ANON_AND_FILE; type++) { > + if (get_nr_gens(lruvec, type) != MAX_NR_GENS) > + continue; I'm confused about relation between aging and LRU list operation. In function inc_max_seq, both min_seq and max_seq will increase， the lrugen->lists[] indexed by lru_gen_from_seq(max_seq + 1) may be non-empty? for example, before inc_max_seq: min_seq == 0, lrugen->lists[0][type][zone] max_seq ==3, lrugen->lists[3][type][zone] after inc_max_seq: min_seq ==1, lrugen->lists[1][type][zone] max_seq ==4, lrugen->lists[0][type][zone] If lrugen->lists[0][type][zone] is not empty before inc_max_seq and it is the most inactive list，however lurgen->lists[0][type][zone] will become the most active list after inc_max_seq. So, in this place, if (get_nr_gens(lruvec, type) != MAX_NR_GENS) continue; should change to if (get_nr_gens(lruvec, type) == MAX_NR_GENS) continue; Or am I missing something? Many thanks. > + > + reset_ctrl_pos(lruvec, type, true); > + WRITE_ONCE(lrugen->min_seq[type], lrugen->min_seq[type] + 1); > + } > +} > + > +static bool try_to_inc_min_seq(struct lruvec *lruvec, bool can_swap) > +{ > + int gen, type, zone; > + bool success = false; > + struct lru_gen_struct *lrugen = &lruvec->lrugen; > + DEFINE_MIN_SEQ(lruvec); > + > + VM_BUG_ON(!seq_is_valid(lruvec)); > + > + for (type = !can_swap; type < ANON_AND_FILE; type++) { > + while (min_seq[type] + MIN_NR_GENS <= lrugen->max_seq) { > + gen = lru_gen_from_seq(min_seq[type]); > + > + for (zone = 0; zone < MAX_NR_ZONES; zone++) { > + if (!list_empty(&lrugen->lists[gen][type][zone])) > + goto next; > + } > + > + min_seq[type]++; > + } > +next: > + ; > + } > + > + /* see the comment on lru_gen_struct */ > + if (can_swap) { > + min_seq[LRU_GEN_ANON] = min(min_seq[LRU_GEN_ANON], min_seq[LRU_GEN_FILE]); > + min_seq[LRU_GEN_FILE] = max(min_seq[LRU_GEN_ANON], lrugen->min_seq[LRU_GEN_FILE]); > + } > + > + for (type = !can_swap; type < ANON_AND_FILE; type++) { > + if (min_seq[type] == lrugen->min_seq[type]) > + continue; > + > + reset_ctrl_pos(lruvec, type, true); > + WRITE_ONCE(lrugen->min_seq[type], min_seq[type]); > + success = true; > + } > + > + return success; > +} > + > +static void inc_max_seq(struct lruvec *lruvec, unsigned long max_seq) > +{ > + int prev, next; > + int type, zone; > + struct lru_gen_struct *lrugen = &lruvec->lrugen; > + > + spin_lock_irq(&lruvec->lru_lock); > + > + VM_BUG_ON(!seq_is_valid(lruvec)); > + > + if (max_seq != lrugen->max_seq) > + goto unlock; > + > + inc_min_seq(lruvec); > + > + /* > + * Update the active/inactive LRU sizes for compatibility. Both sides of > + * the current max_seq need to be covered, since max_seq+1 can overlap > + * with min_seq[LRU_GEN_ANON] if swapping is constrained. And if they do > + * overlap, cold/hot inversion happens. This can be solved by moving > + * pages from min_seq to min_seq+1 but is omitted for simplicity. > + */ > + prev = lru_gen_from_seq(lrugen->max_seq - 1); > + next = lru_gen_from_seq(lrugen->max_seq + 1); > + > + for (type = 0; type < ANON_AND_FILE; type++) { > + for (zone = 0; zone < MAX_NR_ZONES; zone++) { > + enum lru_list lru = type * LRU_INACTIVE_FILE; > + long delta = lrugen->nr_pages[prev][type][zone] - > + lrugen->nr_pages[next][type][zone]; > + > + if (!delta) > + continue; > + > + __update_lru_size(lruvec, lru, zone, delta); > + __update_lru_size(lruvec, lru + LRU_ACTIVE, zone, -delta); > + } > + } > + > + for (type = 0; type < ANON_AND_FILE; type++) > + reset_ctrl_pos(lruvec, type, false); > + > + /* make sure preceding modifications appear */ > + smp_store_release(&lrugen->max_seq, lrugen->max_seq + 1); > +unlock: > + spin_unlock_irq(&lruvec->lru_lock); > +} > + > +static long get_nr_evictable(struct lruvec *lruvec, unsigned long max_seq, > + unsigned long *min_seq, bool can_swap, bool *need_aging) > +{ > + int gen, type, zone; > + long old = 0; > + long young = 0; > + long total = 0; > + struct lru_gen_struct *lrugen = &lruvec->lrugen; > + > + for (type = !can_swap; type < ANON_AND_FILE; type++) { > + unsigned long seq; > + > + for (seq = min_seq[type]; seq <= max_seq; seq++) { > + long size = 0; > + > + gen = lru_gen_from_seq(seq); > + > + for (zone = 0; zone < MAX_NR_ZONES; zone++) > + size += READ_ONCE(lrugen->nr_pages[gen][type][zone]); > + > + total += size; > + if (seq == max_seq) > + young += size; > + if (seq + MIN_NR_GENS == max_seq) > + old += size; > + } > + } > + > + /* > + * The aging and the eviction is a typical producer-consumer model. The > + * aging tries to be lazy to reduce the unnecessary overhead. On the > + * other hand, the eviction stalls when the number of generations > + * reaches MIN_NR_GENS. So ideally, there should be MIN_NR_GENS+1 > + * generations, hence the first two if's. > + * > + * In addition, it's ideal to spread pages out evenly, meaning > + * 1/(MIN_NR_GENS+1) of the total number of pages for each generation. A > + * reasonable range for this average portion would [1/MIN_NR_GENS, > + * 1/(MIN_NR_GENS+2)]. From the consumer's POV, the eviction only cares > + * about the lower bound of cold pages, i.e., 1/(MIN_NR_GENS+2), whereas > + * from the producer's POV, the aging only cares about the upper bound > + * of hot pages, i.e., 1/MIN_NR_GENS. > + */ > + if (min_seq[LRU_GEN_FILE] + MIN_NR_GENS > max_seq) > + *need_aging = true; > + else if (min_seq[LRU_GEN_FILE] + MIN_NR_GENS < max_seq) > + *need_aging = false; > + else if (young * MIN_NR_GENS > total) > + *need_aging = true; > + else if (old * (MIN_NR_GENS + 2) < total) > + *need_aging = true; > + else > + *need_aging = false; > + > + return total > 0 ? total : 0; > +} > + > +static void age_lruvec(struct lruvec *lruvec, struct scan_control *sc) > +{ > + bool need_aging; > + long nr_to_scan; > + int swappiness = get_swappiness(lruvec, sc); > + struct mem_cgroup *memcg = lruvec_memcg(lruvec); > + DEFINE_MAX_SEQ(lruvec); > + DEFINE_MIN_SEQ(lruvec); > + > + mem_cgroup_calculate_protection(NULL, memcg); > + > + if (mem_cgroup_below_min(memcg)) > + return; > + > + nr_to_scan = get_nr_evictable(lruvec, max_seq, min_seq, swappiness, &need_aging); > + if (!nr_to_scan) > + return; > + > + nr_to_scan >>= sc->priority; > + > + if (!mem_cgroup_online(memcg)) > + nr_to_scan++; > + > + if (nr_to_scan && need_aging && (!mem_cgroup_below_low(memcg) || sc->memcg_low_reclaim)) > + inc_max_seq(lruvec, max_seq); > +} > + > +static void lru_gen_age_node(struct pglist_data *pgdat, struct scan_control *sc) > +{ > + struct mem_cgroup *memcg; > + > + VM_BUG_ON(!current_is_kswapd()); > + > + memcg = mem_cgroup_iter(NULL, NULL, NULL); > + do { > + struct lruvec *lruvec = mem_cgroup_lruvec(memcg, pgdat); > + > + age_lruvec(lruvec, sc); > + > + cond_resched(); > + } while ((memcg = mem_cgroup_iter(NULL, memcg, NULL))); > +} > + > +/****************************************************************************** > + * the eviction > + ******************************************************************************/ > + > +static bool sort_folio(struct lruvec *lruvec, struct folio *folio, int tier_idx) > +{ > + bool success; > + int gen = folio_lru_gen(folio); > + int type = folio_is_file_lru(folio); > + int zone = folio_zonenum(folio); > + int tier = folio_lru_tier(folio); > + int delta = folio_nr_pages(folio); > + struct lru_gen_struct *lrugen = &lruvec->lrugen; > + > + VM_BUG_ON_FOLIO(gen >= MAX_NR_GENS, folio); > + > + if (!folio_evictable(folio)) { > + success = lru_gen_del_folio(lruvec, folio, true); > + VM_BUG_ON_FOLIO(!success, folio); > + folio_set_unevictable(folio); > + lruvec_add_folio(lruvec, folio); > + __count_vm_events(UNEVICTABLE_PGCULLED, delta); > + return true; > + } > + > + if (type == LRU_GEN_FILE && folio_test_anon(folio) && folio_test_dirty(folio)) { > + success = lru_gen_del_folio(lruvec, folio, true); > + VM_BUG_ON_FOLIO(!success, folio); > + folio_set_swapbacked(folio); > + lruvec_add_folio_tail(lruvec, folio); > + return true; > + } > + > + if (tier > tier_idx) { > + int hist = lru_hist_from_seq(lrugen->min_seq[type]); > + > + gen = folio_inc_gen(lruvec, folio, false); > + list_move_tail(&folio->lru, &lrugen->lists[gen][type][zone]); > + > + WRITE_ONCE(lrugen->protected[hist][type][tier - 1], > + lrugen->protected[hist][type][tier - 1] + delta); > + __mod_lruvec_state(lruvec, WORKINGSET_ACTIVATE_BASE + type, delta); > + return true; > + } > + > + if (folio_test_locked(folio) || folio_test_writeback(folio) || > + (type == LRU_GEN_FILE && folio_test_dirty(folio))) { > + gen = folio_inc_gen(lruvec, folio, true); > + list_move(&folio->lru, &lrugen->lists[gen][type][zone]); > + return true; > + } > + > + return false; > +} > + > +static bool isolate_folio(struct lruvec *lruvec, struct folio *folio, struct scan_control *sc) > +{ > + bool success; > + > + if (!sc->may_unmap && folio_mapped(folio)) > + return false; > + > + if (!(sc->may_writepage && (sc->gfp_mask & __GFP_IO)) && > + (folio_test_dirty(folio) || > + (folio_test_anon(folio) && !folio_test_swapcache(folio)))) > + return false; > + > + if (!folio_try_get(folio)) > + return false; > + > + if (!folio_test_clear_lru(folio)) { > + folio_put(folio); > + return false; > + } > + > + success = lru_gen_del_folio(lruvec, folio, true); > + VM_BUG_ON_FOLIO(!success, folio); > + > + return true; > +} > + > +static int scan_folios(struct lruvec *lruvec, struct scan_control *sc, > + int type, int tier, struct list_head *list) > +{ > + int gen, zone; > + enum vm_event_item item; > + int sorted = 0; > + int scanned = 0; > + int isolated = 0; > + int remaining = MAX_LRU_BATCH; > + struct lru_gen_struct *lrugen = &lruvec->lrugen; > + struct mem_cgroup *memcg = lruvec_memcg(lruvec); > + > + VM_BUG_ON(!list_empty(list)); > + > + if (get_nr_gens(lruvec, type) == MIN_NR_GENS) > + return 0; > + > + gen = lru_gen_from_seq(lrugen->min_seq[type]); > + > + for (zone = sc->reclaim_idx; zone >= 0; zone--) { > + LIST_HEAD(moved); > + int skipped = 0; > + struct list_head *head = &lrugen->lists[gen][type][zone]; > + > + while (!list_empty(head)) { > + struct folio *folio = lru_to_folio(head); > + int delta = folio_nr_pages(folio); > + > + VM_BUG_ON_FOLIO(folio_test_unevictable(folio), folio); > + VM_BUG_ON_FOLIO(folio_test_active(folio), folio); > + VM_BUG_ON_FOLIO(folio_is_file_lru(folio) != type, folio); > + VM_BUG_ON_FOLIO(folio_zonenum(folio) != zone, folio); > + > + scanned += delta; > + > + if (sort_folio(lruvec, folio, tier)) > + sorted += delta; > + else if (isolate_folio(lruvec, folio, sc)) { > + list_add(&folio->lru, list); > + isolated += delta; > + } else { > + list_move(&folio->lru, &moved); > + skipped += delta; > + } > + > + if (!--remaining || max(isolated, skipped) >= MIN_LRU_BATCH) > + break; > + } > + > + if (skipped) { > + list_splice(&moved, head); > + __count_zid_vm_events(PGSCAN_SKIP, zone, skipped); > + } > + > + if (!remaining || isolated >= MIN_LRU_BATCH) > + break; > + } > + > + item = current_is_kswapd() ? PGSCAN_KSWAPD : PGSCAN_DIRECT; > + if (!cgroup_reclaim(sc)) { > + __count_vm_events(item, isolated); > + __count_vm_events(PGREFILL, sorted); > + } > + __count_memcg_events(memcg, item, isolated); > + __count_memcg_events(memcg, PGREFILL, sorted); > + __count_vm_events(PGSCAN_ANON + type, isolated); > + > + /* > + * There might not be eligible pages due to reclaim_idx, may_unmap and > + * may_writepage. Check the remaining to prevent livelock if there is no > + * progress. > + */ > + return isolated || !remaining ? scanned : 0; > +} > + > +static int get_tier_idx(struct lruvec *lruvec, int type) > +{ > + int tier; > + struct ctrl_pos sp, pv; > + > + /* > + * To leave a margin for fluctuations, use a larger gain factor (1:2). > + * This value is chosen because any other tier would have at least twice > + * as many refaults as the first tier. > + */ > + read_ctrl_pos(lruvec, type, 0, 1, &sp); > + for (tier = 1; tier < MAX_NR_TIERS; tier++) { > + read_ctrl_pos(lruvec, type, tier, 2, &pv); > + if (!positive_ctrl_err(&sp, &pv)) > + break; > + } > + > + return tier - 1; > +} > + > +static int get_type_to_scan(struct lruvec *lruvec, int swappiness, int *tier_idx) > +{ > + int type, tier; > + struct ctrl_pos sp, pv; > + int gain[ANON_AND_FILE] = { swappiness, 200 - swappiness }; > + > + /* > + * Compare the first tier of anon with that of file to determine which > + * type to scan. Also need to compare other tiers of the selected type > + * with the first tier of the other type to determine the last tier (of > + * the selected type) to evict. > + */ > + read_ctrl_pos(lruvec, LRU_GEN_ANON, 0, gain[LRU_GEN_ANON], &sp); > + read_ctrl_pos(lruvec, LRU_GEN_FILE, 0, gain[LRU_GEN_FILE], &pv); > + type = positive_ctrl_err(&sp, &pv); > + > + read_ctrl_pos(lruvec, !type, 0, gain[!type], &sp); > + for (tier = 1; tier < MAX_NR_TIERS; tier++) { > + read_ctrl_pos(lruvec, type, tier, gain[type], &pv); > + if (!positive_ctrl_err(&sp, &pv)) > + break; > + } > + > + *tier_idx = tier - 1; > + > + return type; > +} > + > +static int isolate_folios(struct lruvec *lruvec, struct scan_control *sc, int swappiness, > + int *type_scanned, struct list_head *list) > +{ > + int i; > + int type; > + int scanned; > + int tier = -1; > + DEFINE_MIN_SEQ(lruvec); > + > + VM_BUG_ON(!seq_is_valid(lruvec)); > + > + /* > + * Try to make the obvious choice first. When anon and file are both > + * available from the same generation, interpret swappiness 1 as file > + * first and 200 as anon first. > + */ > + if (!swappiness) > + type = LRU_GEN_FILE; > + else if (min_seq[LRU_GEN_ANON] < min_seq[LRU_GEN_FILE]) > + type = LRU_GEN_ANON; > + else if (swappiness == 1) > + type = LRU_GEN_FILE; > + else if (swappiness == 200) > + type = LRU_GEN_ANON; > + else > + type = get_type_to_scan(lruvec, swappiness, &tier); > + > + for (i = !swappiness; i < ANON_AND_FILE; i++) { > + if (tier < 0) > + tier = get_tier_idx(lruvec, type); > + > + scanned = scan_folios(lruvec, sc, type, tier, list); > + if (scanned) > + break; > + > + type = !type; > + tier = -1; > + } > + > + *type_scanned = type; > + > + return scanned; > +} > + > +static int evict_folios(struct lruvec *lruvec, struct scan_control *sc, int swappiness) > +{ > + int type; > + int scanned; > + int reclaimed; > + LIST_HEAD(list); > + struct folio *folio; > + enum vm_event_item item; > + struct reclaim_stat stat; > + struct mem_cgroup *memcg = lruvec_memcg(lruvec); > + struct pglist_data *pgdat = lruvec_pgdat(lruvec); > + > + spin_lock_irq(&lruvec->lru_lock); > + > + scanned = isolate_folios(lruvec, sc, swappiness, &type, &list); > + > + if (try_to_inc_min_seq(lruvec, swappiness)) > + scanned++; > + > + if (get_nr_gens(lruvec, LRU_GEN_FILE) == MIN_NR_GENS) > + scanned = 0; > + > + spin_unlock_irq(&lruvec->lru_lock); > + > + if (list_empty(&list)) > + return scanned; > + > + reclaimed = shrink_page_list(&list, pgdat, sc, &stat, false); > + > + /* > + * To avoid livelock, don't add rejected pages back to the same lists > + * they were isolated from. See lru_gen_add_folio(). > + */ > + list_for_each_entry(folio, &list, lru) { > + folio_clear_referenced(folio); > + folio_clear_workingset(folio); > + > + if (folio_test_reclaim(folio) && > + (folio_test_dirty(folio) || folio_test_writeback(folio))) > + folio_clear_active(folio); > + else > + folio_set_active(folio); > + } > + > + spin_lock_irq(&lruvec->lru_lock); > + > + move_pages_to_lru(lruvec, &list); > + > + item = current_is_kswapd() ? PGSTEAL_KSWAPD : PGSTEAL_DIRECT; > + if (!cgroup_reclaim(sc)) > + __count_vm_events(item, reclaimed); > + __count_memcg_events(memcg, item, reclaimed); > + __count_vm_events(PGSTEAL_ANON + type, reclaimed); > + > + spin_unlock_irq(&lruvec->lru_lock); > + > + mem_cgroup_uncharge_list(&list); > + free_unref_page_list(&list); > + > + sc->nr_reclaimed += reclaimed; > + > + return scanned; > +} > + > +static long get_nr_to_scan(struct lruvec *lruvec, struct scan_control *sc, bool can_swap) > +{ > + bool need_aging; > + long nr_to_scan; > + struct mem_cgroup *memcg = lruvec_memcg(lruvec); > + DEFINE_MAX_SEQ(lruvec); > + DEFINE_MIN_SEQ(lruvec); > + > + if (mem_cgroup_below_min(memcg) || > + (mem_cgroup_below_low(memcg) && !sc->memcg_low_reclaim)) > + return 0; > + > + nr_to_scan = get_nr_evictable(lruvec, max_seq, min_seq, can_swap, &need_aging); > + if (!nr_to_scan) > + return 0; > + > + /* reset the priority if the target has been met */ > + nr_to_scan >>= sc->nr_reclaimed < sc->nr_to_reclaim ? sc->priority : DEF_PRIORITY; > + > + if (!mem_cgroup_online(memcg)) > + nr_to_scan++; > + > + if (!nr_to_scan) > + return 0; > + > + if (!need_aging) > + return nr_to_scan; > + > + /* leave the work to lru_gen_age_node() */ > + if (current_is_kswapd()) > + return 0; > + > + /* try other memcgs before going to the aging path */ > + if (!cgroup_reclaim(sc) && !sc->force_deactivate) { > + sc->skipped_deactivate = true; > + return 0; > + } > + > + inc_max_seq(lruvec, max_seq); > + > + return nr_to_scan; > +} > + > +static void lru_gen_shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc) > +{ > + struct blk_plug plug; > + long scanned = 0; > + > + lru_add_drain(); > + > + blk_start_plug(&plug); > + > + while (true) { > + int delta; > + int swappiness; > + long nr_to_scan; > + > + if (sc->may_swap) > + swappiness = get_swappiness(lruvec, sc); > + else if (!cgroup_reclaim(sc) && get_swappiness(lruvec, sc)) > + swappiness = 1; > + else > + swappiness = 0; > + > + nr_to_scan = get_nr_to_scan(lruvec, sc, swappiness); > + if (!nr_to_scan) > + break; > + > + delta = evict_folios(lruvec, sc, swappiness); > + if (!delta) > + break; > + > + scanned += delta; > + if (scanned >= nr_to_scan) > + break; > + > + cond_resched(); > + } > + > + blk_finish_plug(&plug); > +} > + > /****************************************************************************** > * initialization > ******************************************************************************/ > @@ -3041,6 +3821,16 @@ static int __init init_lru_gen(void) > }; > late_initcall(init_lru_gen); > > +#else > + > +static void lru_gen_age_node(struct pglist_data *pgdat, struct scan_control *sc) > +{ > +} > + > +static void lru_gen_shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc) > +{ > +} > + > #endif /* CONFIG_LRU_GEN */ > > static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc) > @@ -3054,6 +3844,11 @@ static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc) > struct blk_plug plug; > bool scan_adjusted; > > + if (lru_gen_enabled()) { > + lru_gen_shrink_lruvec(lruvec, sc); > + return; > + } > + > get_scan_count(lruvec, sc, nr); > > /* Record the original scan target for proportional adjustments later */ > @@ -3558,6 +4353,9 @@ static void snapshot_refaults(struct mem_cgroup *target_memcg, pg_data_t *pgdat) > struct lruvec *target_lruvec; > unsigned long refaults; > > + if (lru_gen_enabled()) > + return; > + > target_lruvec = mem_cgroup_lruvec(target_memcg, pgdat); > refaults = lruvec_page_state(target_lruvec, WORKINGSET_ACTIVATE_ANON); > target_lruvec->refaults[0] = refaults; > @@ -3928,6 +4726,11 @@ static void age_active_anon(struct pglist_data *pgdat, > struct mem_cgroup *memcg; > struct lruvec *lruvec; > > + if (lru_gen_enabled()) { > + lru_gen_age_node(pgdat, sc); > + return; > + } > + > if (!can_age_anon_pages(pgdat, sc)) > return; > > diff --git a/mm/workingset.c b/mm/workingset.c > index 8a3828acc0bf..89b46af74eef 100644 > --- a/mm/workingset.c > +++ b/mm/workingset.c > @@ -187,7 +187,6 @@ static unsigned int bucket_order __read_mostly; > static void *pack_shadow(int memcgid, pg_data_t *pgdat, unsigned long eviction, > bool workingset) > { > - eviction >>= bucket_order; > eviction &= EVICTION_MASK; > eviction = (eviction << MEM_CGROUP_ID_SHIFT) | memcgid; > eviction = (eviction << NODES_SHIFT) | pgdat->node_id; > @@ -212,10 +211,116 @@ static void unpack_shadow(void *shadow, int *memcgidp, pg_data_t **pgdat, > > *memcgidp = memcgid; > *pgdat = NODE_DATA(nid); > - *evictionp = entry << bucket_order; > + *evictionp = entry; > *workingsetp = workingset; > } > > +#ifdef CONFIG_LRU_GEN > + > +static int folio_lru_refs(struct folio *folio) > +{ > + unsigned long flags = READ_ONCE(folio->flags); > + > + BUILD_BUG_ON(LRU_GEN_WIDTH + LRU_REFS_WIDTH > BITS_PER_LONG - EVICTION_SHIFT); > + > + /* see the comment on MAX_NR_TIERS */ > + return flags & BIT(PG_workingset) ? (flags & LRU_REFS_MASK) >> LRU_REFS_PGOFF : 0; > +} > + > +static void *lru_gen_eviction(struct folio *folio) > +{ > + int hist, tier; > + unsigned long token; > + unsigned long min_seq; > + struct lruvec *lruvec; > + struct lru_gen_struct *lrugen; > + int type = folio_is_file_lru(folio); > + int refs = folio_lru_refs(folio); > + int delta = folio_nr_pages(folio); > + bool workingset = folio_test_workingset(folio); > + struct mem_cgroup *memcg = folio_memcg(folio); > + struct pglist_data *pgdat = folio_pgdat(folio); > + > + lruvec = mem_cgroup_lruvec(memcg, pgdat); > + lrugen = &lruvec->lrugen; > + min_seq = READ_ONCE(lrugen->min_seq[type]); > + token = (min_seq << LRU_REFS_WIDTH) | refs; > + > + hist = lru_hist_from_seq(min_seq); > + tier = lru_tier_from_refs(refs + workingset); > + atomic_long_add(delta, &lrugen->evicted[hist][type][tier]); > + > + return pack_shadow(mem_cgroup_id(memcg), pgdat, token, workingset); > +} > + > +static void lru_gen_refault(struct folio *folio, void *shadow) > +{ > + int hist, tier, refs; > + int memcg_id; > + bool workingset; > + unsigned long token; > + unsigned long min_seq; > + struct lruvec *lruvec; > + struct lru_gen_struct *lrugen; > + struct mem_cgroup *memcg; > + struct pglist_data *pgdat; > + int type = folio_is_file_lru(folio); > + int delta = folio_nr_pages(folio); > + > + unpack_shadow(shadow, &memcg_id, &pgdat, &token, &workingset); > + > + refs = token & (BIT(LRU_REFS_WIDTH) - 1); > + if (refs && !workingset) > + return; > + > + if (folio_pgdat(folio) != pgdat) > + return; > + > + rcu_read_lock(); > + memcg = folio_memcg_rcu(folio); > + if (mem_cgroup_id(memcg) != memcg_id) > + goto unlock; > + > + token >>= LRU_REFS_WIDTH; > + lruvec = mem_cgroup_lruvec(memcg, pgdat); > + lrugen = &lruvec->lrugen; > + min_seq = READ_ONCE(lrugen->min_seq[type]); > + if (token != (min_seq & (EVICTION_MASK >> LRU_REFS_WIDTH))) > + goto unlock; > + > + hist = lru_hist_from_seq(min_seq); > + tier = lru_tier_from_refs(refs + workingset); > + atomic_long_add(delta, &lrugen->refaulted[hist][type][tier]); > + mod_lruvec_state(lruvec, WORKINGSET_REFAULT_BASE + type, delta); > + > + /* > + * Count the following two cases as stalls: > + * 1. For pages accessed through page tables, hotter pages pushed out > + * hot pages which refaulted immediately. > + * 2. For pages accessed through file descriptors, numbers of accesses > + * might have been beyond the limit. > + */ > + if (lru_gen_in_fault() || refs + workingset == BIT(LRU_REFS_WIDTH)) { > + folio_set_workingset(folio); > + mod_lruvec_state(lruvec, WORKINGSET_RESTORE_BASE + type, delta); > + } > +unlock: > + rcu_read_unlock(); > +} > + > +#else > + > +static void *lru_gen_eviction(struct folio *folio) > +{ > + return NULL; > +} > + > +static void lru_gen_refault(struct folio *folio, void *shadow) > +{ > +} > + > +#endif /* CONFIG_LRU_GEN */ > + > /** > * workingset_age_nonresident - age non-resident entries as LRU ages > * @lruvec: the lruvec that was aged > @@ -264,10 +369,14 @@ void *workingset_eviction(struct folio *folio, struct mem_cgroup *target_memcg) > VM_BUG_ON_FOLIO(folio_ref_count(folio), folio); > VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio); > > + if (lru_gen_enabled()) > + return lru_gen_eviction(folio); > + > lruvec = mem_cgroup_lruvec(target_memcg, pgdat); > /* XXX: target_memcg can be NULL, go through lruvec */ > memcgid = mem_cgroup_id(lruvec_memcg(lruvec)); > eviction = atomic_long_read(&lruvec->nonresident_age); > + eviction >>= bucket_order; > workingset_age_nonresident(lruvec, folio_nr_pages(folio)); > return pack_shadow(memcgid, pgdat, eviction, > folio_test_workingset(folio)); > @@ -298,7 +407,13 @@ void workingset_refault(struct folio *folio, void *shadow) > int memcgid; > long nr; > > + if (lru_gen_enabled()) { > + lru_gen_refault(folio, shadow); > + return; > + } > + > unpack_shadow(shadow, &memcgid, &pgdat, &eviction, &workingset); > + eviction <<= bucket_order; > > rcu_read_lock(); > /*
On Thu, Apr 14, 2022 at 06:03:10PM +1200, Barry Song wrote: > > On Thu, Apr 7, 2022 at 3:16 PM Yu Zhao <yuzhao@google.com> wrote: > > > > + > > +static int isolate_folios(struct lruvec *lruvec, struct scan_control *sc, int swappiness, > > + int *type_scanned, struct list_head *list) > > +{ > > + int i; > > + int type; > > + int scanned; > > + int tier = -1; > > + DEFINE_MIN_SEQ(lruvec); > > + > > + VM_BUG_ON(!seq_is_valid(lruvec)); > > + > > + /* > > + * Try to make the obvious choice first. When anon and file are both > > + * available from the same generation, interpret swappiness 1 as file > > + * first and 200 as anon first. > > + */ > > Has this changed the ABI of swapiness? No. > or it is only something > meaningful for the internal code? This is how swappiness is interpreted. > if so, can we rename it to > something else? otherwise, it is quite confusing. Feel free to suggest something. > it seems 1 is set internally as a magic number here: > +static void lru_gen_shrink_lruvec(struct lruvec *lruvec, struct > scan_control *sc) > +{ > + ... > + else if (!cgroup_reclaim(sc) && get_swappiness(lruvec, sc)) > + swappiness = 1; > + else > + swappiness = 0; > + } > obviously this swappiness is neither /proc/sys/vm/swappiness nor > /sys/fs/cgroup/memory/<group>/>memory.swappiness, right? Right. > > @@ -3928,6 +4726,11 @@ static void age_active_anon(struct pglist_data *pgdat, > > struct mem_cgroup *memcg; > > struct lruvec *lruvec; > > > > + if (lru_gen_enabled()) { > > + lru_gen_age_node(pgdat, sc); > > + return; > > + } > > is it really a good place for lru_gen_age_node() since the function > is named age_active_anon() > but here you are doing aging for both anon and file pages? Yes. > obviously > lru_gen_age_node() is not > doing "age active anon". We can rename it if you have something in mind.
On Thu, Apr 14, 2022 at 07:47:54PM +0800, Chen Wandun wrote: > > On 2022/4/7 11:15, Yu Zhao wrote: > > +static void inc_min_seq(struct lruvec *lruvec) > > +{ > > + int type; > > + struct lru_gen_struct *lrugen = &lruvec->lrugen; > > + > > + VM_BUG_ON(!seq_is_valid(lruvec)); > > + > > + for (type = 0; type < ANON_AND_FILE; type++) { > > + if (get_nr_gens(lruvec, type) != MAX_NR_GENS) > > + continue; > I'm confused about relation between aging and LRU list operation. > > In function inc_max_seq, both min_seq and max_seq will increase， > the lrugen->lists[] indexed by lru_gen_from_seq(max_seq + 1) may > be non-empty? Yes. > for example, > before inc_max_seq: > min_seq == 0, lrugen->lists[0][type][zone] > max_seq ==3, lrugen->lists[3][type][zone] > > after inc_max_seq: > min_seq ==1, lrugen->lists[1][type][zone] > max_seq ==4, lrugen->lists[0][type][zone] > > If lrugen->lists[0][type][zone] is not empty before inc_max_seq and it is > the most inactive list，however lurgen->lists[0][type][zone] will become > the most active list after inc_max_seq. Correct. > So, in this place, > > if (get_nr_gens(lruvec, type) != MAX_NR_GENS) > continue; > > should change to > > if (get_nr_gens(lruvec, type) == MAX_NR_GENS) > continue; No, because max/min_seq will overlap if we do so. lrugen->lists[max_seq+1] can only be non-empty for anon LRU, for a couple of reasons: 1. We can't swap at all. 2. Swapping is constrained, e.g., swapfile is full. Both cases are similar to a producer (the aging) overrunning a consumer (the eviction). We used to handle them, but I simplified the code because I don't feel they are worth handling [1]. [1] https://lore.kernel.org/r/CAOUHufbDfwgm8PgCGkhCjbhMbm=fekfjgRR56NL-j+5iUGfVuw@mail.gmail.com/
On Thu, 14 Apr 2022 14:36:03 -0600 Yu Zhao <yuzhao@google.com> wrote: > > or it is only something > > meaningful for the internal code? > > This is how swappiness is interpreted. > > > if so, can we rename it to > > something else? otherwise, it is quite confusing. > > Feel free to suggest something. It is confusing, swap_preference?
On Thu, Apr 14, 2022 at 3:40 PM Andrew Morton <akpm@linux-foundation.org> wrote: > > On Thu, 14 Apr 2022 14:36:03 -0600 Yu Zhao <yuzhao@google.com> wrote: > > > > or it is only something > > > meaningful for the internal code? > > > > This is how swappiness is interpreted. > > > > > if so, can we rename it to > > > something else? otherwise, it is quite confusing. > > > > Feel free to suggest something. > > It is confusing, swap_preference? It's still largely swappiness -- the original swappiness is twisted a bit around the corners (0, 1 and 200) to make it more suitable for internal use. I vote for __swappiness or lrugen_swappiness, which look ugly to me but it captures what this variable actually is, i.e., an overridden version of the original swappiness. And similar for lru_gen_mm_walk *walk vs mm_walk *walk. In other languages where polymorphism is supported, there are established naming conversions. In this patchset, I just used the same variable name when two things are closely related but distinguishable from the _contexts_ they are used.
在 2022/4/15 4:53, Yu Zhao 写道: > On Thu, Apr 14, 2022 at 07:47:54PM +0800, Chen Wandun wrote: >> On 2022/4/7 11:15, Yu Zhao wrote: >>> +static void inc_min_seq(struct lruvec *lruvec) >>> +{ >>> + int type; >>> + struct lru_gen_struct *lrugen = &lruvec->lrugen; >>> + >>> + VM_BUG_ON(!seq_is_valid(lruvec)); >>> + >>> + for (type = 0; type < ANON_AND_FILE; type++) { >>> + if (get_nr_gens(lruvec, type) != MAX_NR_GENS) >>> + continue; >> I'm confused about relation between aging and LRU list operation. >> >> In function inc_max_seq, both min_seq and max_seq will increase， >> the lrugen->lists[] indexed by lru_gen_from_seq(max_seq + 1) may >> be non-empty? > Yes. > >> for example, >> before inc_max_seq: >> min_seq == 0, lrugen->lists[0][type][zone] >> max_seq ==3, lrugen->lists[3][type][zone] >> >> after inc_max_seq: >> min_seq ==1, lrugen->lists[1][type][zone] >> max_seq ==4, lrugen->lists[0][type][zone] >> >> If lrugen->lists[0][type][zone] is not empty before inc_max_seq and it is >> the most inactive list，however lurgen->lists[0][type][zone] will become >> the most active list after inc_max_seq. > Correct. > >> So, in this place, >> >> if (get_nr_gens(lruvec, type) != MAX_NR_GENS) >> continue; >> >> should change to >> >> if (get_nr_gens(lruvec, type) == MAX_NR_GENS) >> continue; > No, because max/min_seq will overlap if we do so. > > lrugen->lists[max_seq+1] can only be non-empty for anon LRU, for a > couple of reasons: > 1. We can't swap at all. > 2. Swapping is constrained, e.g., swapfile is full. > > Both cases are similar to a producer (the aging) overrunning a > consumer (the eviction). We used to handle them, but I simplified the > code because I don't feel they are worth handling [1]. Can lrugen->lists[max_seq+1] also be non-empty for file LRU？ such as in dont reclaim mapped file page case(isolation will fail). If so, after aging, eviction will reclaim memory start from lrugen->lists[min_seq+1], but some oldest file page still remain in lrugen->lists[max_seq+1]. sort_folio can help to put misplaced pages to the right LRU list, but in this case, it does't help, because sort_folio only sort lrugen->lists[min_seq+1]. Thanks Wandun > > [1] https://lore.kernel.org/r/CAOUHufbDfwgm8PgCGkhCjbhMbm=fekfjgRR56NL-j+5iUGfVuw@mail.gmail.com/ > .
On Fri, Apr 15, 2022 at 10:23:18AM +0800, Chen Wandun wrote: > > 在 2022/4/15 4:53, Yu Zhao 写道: > > On Thu, Apr 14, 2022 at 07:47:54PM +0800, Chen Wandun wrote: > > > On 2022/4/7 11:15, Yu Zhao wrote: > > > > +static void inc_min_seq(struct lruvec *lruvec) > > > > +{ > > > > + int type; > > > > + struct lru_gen_struct *lrugen = &lruvec->lrugen; > > > > + > > > > + VM_BUG_ON(!seq_is_valid(lruvec)); > > > > + > > > > + for (type = 0; type < ANON_AND_FILE; type++) { > > > > + if (get_nr_gens(lruvec, type) != MAX_NR_GENS) > > > > + continue; > > > I'm confused about relation between aging and LRU list operation. > > > > > > In function inc_max_seq, both min_seq and max_seq will increase， > > > the lrugen->lists[] indexed by lru_gen_from_seq(max_seq + 1) may > > > be non-empty? > > Yes. > > > > > for example, > > > before inc_max_seq: > > > min_seq == 0, lrugen->lists[0][type][zone] > > > max_seq ==3, lrugen->lists[3][type][zone] > > > > > > after inc_max_seq: > > > min_seq ==1, lrugen->lists[1][type][zone] > > > max_seq ==4, lrugen->lists[0][type][zone] > > > > > > If lrugen->lists[0][type][zone] is not empty before inc_max_seq and it is > > > the most inactive list，however lurgen->lists[0][type][zone] will become > > > the most active list after inc_max_seq. > > Correct. > > > > > So, in this place, > > > > > > if (get_nr_gens(lruvec, type) != MAX_NR_GENS) > > > continue; > > > > > > should change to > > > > > > if (get_nr_gens(lruvec, type) == MAX_NR_GENS) > > > continue; > > No, because max/min_seq will overlap if we do so. > > > > lrugen->lists[max_seq+1] can only be non-empty for anon LRU, for a > > couple of reasons: > > 1. We can't swap at all. > > 2. Swapping is constrained, e.g., swapfile is full. > > > > Both cases are similar to a producer (the aging) overrunning a > > consumer (the eviction). We used to handle them, but I simplified the > > code because I don't feel they are worth handling [1]. > > Can lrugen->lists[max_seq+1] also be non-empty for file LRU？ On reclaim path, no. But it can be forced to do so via debugfs. > such as in dont reclaim mapped file page case(isolation will fail). You mean may_unmap=false? Pages stays in the same generation if isolation fails. So lrugen->lists[min_seq] won't be empty in this case. > If so, after aging, eviction will reclaim memory start from > lrugen->lists[min_seq+1], but some oldest file page still > remain in lrugen->lists[max_seq+1]. > > sort_folio can help to put misplaced pages to the right > LRU list, but in this case, it does't help, because sort_folio > only sort lrugen->lists[min_seq+1]. On reclaim path, inc_max_seq() is only called when need_aging=true, and this guarantees max_seq-min_seq[LRU_GEN_FILE]+1 < MAX_NR_GENS.
在 2022/4/15 13:25, Yu Zhao 写道: > On Fri, Apr 15, 2022 at 10:23:18AM +0800, Chen Wandun wrote: >> 在 2022/4/15 4:53, Yu Zhao 写道: >>> On Thu, Apr 14, 2022 at 07:47:54PM +0800, Chen Wandun wrote: >>>> On 2022/4/7 11:15, Yu Zhao wrote: >>>>> +static void inc_min_seq(struct lruvec *lruvec) >>>>> +{ >>>>> + int type; >>>>> + struct lru_gen_struct *lrugen = &lruvec->lrugen; >>>>> + >>>>> + VM_BUG_ON(!seq_is_valid(lruvec)); >>>>> + >>>>> + for (type = 0; type < ANON_AND_FILE; type++) { >>>>> + if (get_nr_gens(lruvec, type) != MAX_NR_GENS) >>>>> + continue; >>>> I'm confused about relation between aging and LRU list operation. >>>> >>>> In function inc_max_seq, both min_seq and max_seq will increase， >>>> the lrugen->lists[] indexed by lru_gen_from_seq(max_seq + 1) may >>>> be non-empty? >>> Yes. >>> >>>> for example, >>>> before inc_max_seq: >>>> min_seq == 0, lrugen->lists[0][type][zone] >>>> max_seq ==3, lrugen->lists[3][type][zone] >>>> >>>> after inc_max_seq: >>>> min_seq ==1, lrugen->lists[1][type][zone] >>>> max_seq ==4, lrugen->lists[0][type][zone] >>>> >>>> If lrugen->lists[0][type][zone] is not empty before inc_max_seq and it is >>>> the most inactive list，however lurgen->lists[0][type][zone] will become >>>> the most active list after inc_max_seq. >>> Correct. >>> >>>> So, in this place, >>>> >>>> if (get_nr_gens(lruvec, type) != MAX_NR_GENS) >>>> continue; >>>> >>>> should change to >>>> >>>> if (get_nr_gens(lruvec, type) == MAX_NR_GENS) >>>> continue; >>> No, because max/min_seq will overlap if we do so. >>> >>> lrugen->lists[max_seq+1] can only be non-empty for anon LRU, for a >>> couple of reasons: >>> 1. We can't swap at all. >>> 2. Swapping is constrained, e.g., swapfile is full. >>> >>> Both cases are similar to a producer (the aging) overrunning a >>> consumer (the eviction). We used to handle them, but I simplified the >>> code because I don't feel they are worth handling [1]. >> Can lrugen->lists[max_seq+1] also be non-empty for file LRU？ > On reclaim path, no. But it can be forced to do so via debugfs. > >> such as in dont reclaim mapped file page case(isolation will fail). > You mean may_unmap=false? Pages stays in the same generation if > isolation fails. So lrugen->lists[min_seq] won't be empty in this > case. > >> If so, after aging, eviction will reclaim memory start from >> lrugen->lists[min_seq+1], but some oldest file page still >> remain in lrugen->lists[max_seq+1]. >> >> sort_folio can help to put misplaced pages to the right >> LRU list, but in this case, it does't help, because sort_folio >> only sort lrugen->lists[min_seq+1]. > On reclaim path, inc_max_seq() is only called when need_aging=true, > and this guarantees max_seq-min_seq[LRU_GEN_FILE]+1 < MAX_NR_GENS. yes, I think so, but I did't find the logical in function get_nr_evictable, or am I missing something if (min_seq[LRU_GEN_FILE] + MIN_NR_GENS > max_seq) *need_aging = true; else if (min_seq[LRU_GEN_FILE] + MIN_NR_GENS < max_seq) *need_aging = false; else if (young * MIN_NR_GENS > total) *need_aging = true; else if (old * (MIN_NR_GENS + 2) < total) *need_aging = true; else *need_aging = false; Thanks > .
On Fri, Apr 15, 2022 at 02:31:37PM +0800, Chen Wandun wrote: > > > 在 2022/4/15 13:25, Yu Zhao 写道: > > On Fri, Apr 15, 2022 at 10:23:18AM +0800, Chen Wandun wrote: > > > 在 2022/4/15 4:53, Yu Zhao 写道: > > > > On Thu, Apr 14, 2022 at 07:47:54PM +0800, Chen Wandun wrote: > > > > > On 2022/4/7 11:15, Yu Zhao wrote: > > > > > > +static void inc_min_seq(struct lruvec *lruvec) > > > > > > +{ > > > > > > + int type; > > > > > > + struct lru_gen_struct *lrugen = &lruvec->lrugen; > > > > > > + > > > > > > + VM_BUG_ON(!seq_is_valid(lruvec)); > > > > > > + > > > > > > + for (type = 0; type < ANON_AND_FILE; type++) { > > > > > > + if (get_nr_gens(lruvec, type) != MAX_NR_GENS) > > > > > > + continue; > > > > > I'm confused about relation between aging and LRU list operation. > > > > > > > > > > In function inc_max_seq, both min_seq and max_seq will increase， > > > > > the lrugen->lists[] indexed by lru_gen_from_seq(max_seq + 1) may > > > > > be non-empty? > > > > Yes. > > > > > > > > > for example, > > > > > before inc_max_seq: > > > > > min_seq == 0, lrugen->lists[0][type][zone] > > > > > max_seq ==3, lrugen->lists[3][type][zone] > > > > > > > > > > after inc_max_seq: > > > > > min_seq ==1, lrugen->lists[1][type][zone] > > > > > max_seq ==4, lrugen->lists[0][type][zone] > > > > > > > > > > If lrugen->lists[0][type][zone] is not empty before inc_max_seq and it is > > > > > the most inactive list，however lurgen->lists[0][type][zone] will become > > > > > the most active list after inc_max_seq. > > > > Correct. > > > > > > > > > So, in this place, > > > > > > > > > > if (get_nr_gens(lruvec, type) != MAX_NR_GENS) > > > > > continue; > > > > > > > > > > should change to > > > > > > > > > > if (get_nr_gens(lruvec, type) == MAX_NR_GENS) > > > > > continue; > > > > No, because max/min_seq will overlap if we do so. > > > > > > > > lrugen->lists[max_seq+1] can only be non-empty for anon LRU, for a > > > > couple of reasons: > > > > 1. We can't swap at all. > > > > 2. Swapping is constrained, e.g., swapfile is full. > > > > > > > > Both cases are similar to a producer (the aging) overrunning a > > > > consumer (the eviction). We used to handle them, but I simplified the > > > > code because I don't feel they are worth handling [1]. > > > Can lrugen->lists[max_seq+1] also be non-empty for file LRU？ > > On reclaim path, no. But it can be forced to do so via debugfs. > > > > > such as in dont reclaim mapped file page case(isolation will fail). > > You mean may_unmap=false? Pages stays in the same generation if > > isolation fails. So lrugen->lists[min_seq] won't be empty in this > > case. > > > > > If so, after aging, eviction will reclaim memory start from > > > lrugen->lists[min_seq+1], but some oldest file page still > > > remain in lrugen->lists[max_seq+1]. > > > > > > sort_folio can help to put misplaced pages to the right > > > LRU list, but in this case, it does't help, because sort_folio > > > only sort lrugen->lists[min_seq+1]. > > On reclaim path, inc_max_seq() is only called when need_aging=true, > > and this guarantees max_seq-min_seq[LRU_GEN_FILE]+1 < MAX_NR_GENS. > yes, I think so, but I did't find the logical in function get_nr_evictable, > or am I missing something > > if (min_seq[LRU_GEN_FILE] + MIN_NR_GENS > max_seq) > *need_aging = true; > else if (min_seq[LRU_GEN_FILE] + MIN_NR_GENS < max_seq) > *need_aging = false; This branch. And the following is also relavent: static int __init init_lru_gen(void) { BUILD_BUG_ON(MIN_NR_GENS + 1 >= MAX_NR_GENS);
在 2022/4/15 14:44, Yu Zhao 写道: > On Fri, Apr 15, 2022 at 02:31:37PM +0800, Chen Wandun wrote: >> >> 在 2022/4/15 13:25, Yu Zhao 写道: >>> On Fri, Apr 15, 2022 at 10:23:18AM +0800, Chen Wandun wrote: >>>> 在 2022/4/15 4:53, Yu Zhao 写道: >>>>> On Thu, Apr 14, 2022 at 07:47:54PM +0800, Chen Wandun wrote: >>>>>> On 2022/4/7 11:15, Yu Zhao wrote: >>>>>>> +static void inc_min_seq(struct lruvec *lruvec) >>>>>>> +{ >>>>>>> + int type; >>>>>>> + struct lru_gen_struct *lrugen = &lruvec->lrugen; >>>>>>> + >>>>>>> + VM_BUG_ON(!seq_is_valid(lruvec)); >>>>>>> + >>>>>>> + for (type = 0; type < ANON_AND_FILE; type++) { >>>>>>> + if (get_nr_gens(lruvec, type) != MAX_NR_GENS) >>>>>>> + continue; >>>>>> I'm confused about relation between aging and LRU list operation. >>>>>> >>>>>> In function inc_max_seq, both min_seq and max_seq will increase， >>>>>> the lrugen->lists[] indexed by lru_gen_from_seq(max_seq + 1) may >>>>>> be non-empty? >>>>> Yes. >>>>> >>>>>> for example, >>>>>> before inc_max_seq: >>>>>> min_seq == 0, lrugen->lists[0][type][zone] >>>>>> max_seq ==3, lrugen->lists[3][type][zone] >>>>>> >>>>>> after inc_max_seq: >>>>>> min_seq ==1, lrugen->lists[1][type][zone] >>>>>> max_seq ==4, lrugen->lists[0][type][zone] >>>>>> >>>>>> If lrugen->lists[0][type][zone] is not empty before inc_max_seq and it is >>>>>> the most inactive list，however lurgen->lists[0][type][zone] will become >>>>>> the most active list after inc_max_seq. >>>>> Correct. >>>>> >>>>>> So, in this place, >>>>>> >>>>>> if (get_nr_gens(lruvec, type) != MAX_NR_GENS) >>>>>> continue; >>>>>> >>>>>> should change to >>>>>> >>>>>> if (get_nr_gens(lruvec, type) == MAX_NR_GENS) >>>>>> continue; >>>>> No, because max/min_seq will overlap if we do so. >>>>> >>>>> lrugen->lists[max_seq+1] can only be non-empty for anon LRU, for a >>>>> couple of reasons: >>>>> 1. We can't swap at all. >>>>> 2. Swapping is constrained, e.g., swapfile is full. >>>>> >>>>> Both cases are similar to a producer (the aging) overrunning a >>>>> consumer (the eviction). We used to handle them, but I simplified the >>>>> code because I don't feel they are worth handling [1]. >>>> Can lrugen->lists[max_seq+1] also be non-empty for file LRU？ >>> On reclaim path, no. But it can be forced to do so via debugfs. >>> >>>> such as in dont reclaim mapped file page case(isolation will fail). >>> You mean may_unmap=false? Pages stays in the same generation if >>> isolation fails. So lrugen->lists[min_seq] won't be empty in this >>> case. >>> >>>> If so, after aging, eviction will reclaim memory start from >>>> lrugen->lists[min_seq+1], but some oldest file page still >>>> remain in lrugen->lists[max_seq+1]. >>>> >>>> sort_folio can help to put misplaced pages to the right >>>> LRU list, but in this case, it does't help, because sort_folio >>>> only sort lrugen->lists[min_seq+1]. >>> On reclaim path, inc_max_seq() is only called when need_aging=true, >>> and this guarantees max_seq-min_seq[LRU_GEN_FILE]+1 < MAX_NR_GENS. >> yes, I think so, but I did't find the logical in function get_nr_evictable, >> or am I missing something >> >> if (min_seq[LRU_GEN_FILE] + MIN_NR_GENS > max_seq) >> *need_aging = true; >> else if (min_seq[LRU_GEN_FILE] + MIN_NR_GENS < max_seq) >> *need_aging = false; > This branch. > > And the following is also relavent: > > static int __init init_lru_gen(void) > { > BUILD_BUG_ON(MIN_NR_GENS + 1 >= MAX_NR_GENS); Got it, many thanks. Wandun > .
On Fri, Apr 15, 2022 at 9:40 AM Andrew Morton <akpm@linux-foundation.org> wrote: > > On Thu, 14 Apr 2022 14:36:03 -0600 Yu Zhao <yuzhao@google.com> wrote: > > > > or it is only something > > > meaningful for the internal code? > > > > This is how swappiness is interpreted. > > > > > if so, can we rename it to > > > something else? otherwise, it is quite confusing. > > > > Feel free to suggest something. > > It is confusing, swap_preference? seems to be much better. might also be worth using MACRO to replace those 1, 200, 0 magic numbers to tell readers the exact meaning? > > Thanks Barry
On Fri, Apr 15, 2022 at 8:36 AM Yu Zhao <yuzhao@google.com> wrote: > > On Thu, Apr 14, 2022 at 06:03:10PM +1200, Barry Song wrote: > > > > On Thu, Apr 7, 2022 at 3:16 PM Yu Zhao <yuzhao@google.com> wrote: > > > > > > + > > > +static int isolate_folios(struct lruvec *lruvec, struct scan_control *sc, int swappiness, > > > + int *type_scanned, struct list_head *list) > > > +{ > > > + int i; > > > + int type; > > > + int scanned; > > > + int tier = -1; > > > + DEFINE_MIN_SEQ(lruvec); > > > + > > > + VM_BUG_ON(!seq_is_valid(lruvec)); > > > + > > > + /* > > > + * Try to make the obvious choice first. When anon and file are both > > > + * available from the same generation, interpret swappiness 1 as file > > > + * first and 200 as anon first. > > > + */ > > > > Has this changed the ABI of swapiness? > > No. > > > or it is only something > > meaningful for the internal code? > > This is how swappiness is interpreted. > > > if so, can we rename it to > > something else? otherwise, it is quite confusing. > > Feel free to suggest something. > > > it seems 1 is set internally as a magic number here: > > +static void lru_gen_shrink_lruvec(struct lruvec *lruvec, struct > > scan_control *sc) > > +{ > > + ... > > + else if (!cgroup_reclaim(sc) && get_swappiness(lruvec, sc)) > > + swappiness = 1; > > + else > > + swappiness = 0; > > + } > > obviously this swappiness is neither /proc/sys/vm/swappiness nor > > /sys/fs/cgroup/memory/<group>/>memory.swappiness, right? > > Right. > > > > @@ -3928,6 +4726,11 @@ static void age_active_anon(struct pglist_data *pgdat, > > > struct mem_cgroup *memcg; > > > struct lruvec *lruvec; > > > > > > + if (lru_gen_enabled()) { > > > + lru_gen_age_node(pgdat, sc); > > > + return; > > > + } > > > > is it really a good place for lru_gen_age_node() since the function > > is named age_active_anon() > > but here you are doing aging for both anon and file pages? > > Yes. > > > obviously > > lru_gen_age_node() is not > > doing "age active anon". > ;> We can rename it if you have something in mind. i wonder if we can directly do: if (lru_gen_enabled()) lru_gen_age_node(pgdat, sc); else age_active_anon(); rather than: /* * Do some background aging of the anon list, to give * pages a chance to be referenced before reclaiming. All * pages are rotated regardless of classzone as this is * about consistent aging. */ age_active_anon() { if (lru_gen_enabled()) return lru_gen_age_node(pgdat, sc); } the comment above makes no sense to lru_gen_age_node(pgdat, sc); another way is that we can add a wrapper for them as below, age_node() { if (lru_gen_enabled()) return lru_gen_age_node(pgdat, sc); age_active_anon(); } Thanks Barry
On Fri, Apr 15, 2022 at 4:16 AM Barry Song <21cnbao@gmail.com> wrote: > > On Fri, Apr 15, 2022 at 9:40 AM Andrew Morton <akpm@linux-foundation.org> wrote: > > > > On Thu, 14 Apr 2022 14:36:03 -0600 Yu Zhao <yuzhao@google.com> wrote: > > > > > > or it is only something > > > > meaningful for the internal code? > > > > > > This is how swappiness is interpreted. > > > > > > > if so, can we rename it to > > > > something else? otherwise, it is quite confusing. > > > > > > Feel free to suggest something. > > > > It is confusing, swap_preference? > > seems to be much better. might also be worth using MACRO to replace those > 1, 200, 0 magic numbers to tell readers the exact meaning? How do you read "swap_preference=0"? I read it as "no (swap) preference", which means anon and file are equal. The real meaning though, is "don't swap"; and the "no preference" value is actually 100.
On Fri, Apr 15, 2022 at 4:26 AM Barry Song <21cnbao@gmail.com> wrote: > > On Fri, Apr 15, 2022 at 8:36 AM Yu Zhao <yuzhao@google.com> wrote: > > > > On Thu, Apr 14, 2022 at 06:03:10PM +1200, Barry Song wrote: > > > > > > On Thu, Apr 7, 2022 at 3:16 PM Yu Zhao <yuzhao@google.com> wrote: > > > > > > > > + > > > > +static int isolate_folios(struct lruvec *lruvec, struct scan_control *sc, int swappiness, > > > > + int *type_scanned, struct list_head *list) > > > > +{ > > > > + int i; > > > > + int type; > > > > + int scanned; > > > > + int tier = -1; > > > > + DEFINE_MIN_SEQ(lruvec); > > > > + > > > > + VM_BUG_ON(!seq_is_valid(lruvec)); > > > > + > > > > + /* > > > > + * Try to make the obvious choice first. When anon and file are both > > > > + * available from the same generation, interpret swappiness 1 as file > > > > + * first and 200 as anon first. > > > > + */ > > > > > > Has this changed the ABI of swapiness? > > > > No. > > > > > or it is only something > > > meaningful for the internal code? > > > > This is how swappiness is interpreted. > > > > > if so, can we rename it to > > > something else? otherwise, it is quite confusing. > > > > Feel free to suggest something. > > > > > it seems 1 is set internally as a magic number here: > > > +static void lru_gen_shrink_lruvec(struct lruvec *lruvec, struct > > > scan_control *sc) > > > +{ > > > + ... > > > + else if (!cgroup_reclaim(sc) && get_swappiness(lruvec, sc)) > > > + swappiness = 1; > > > + else > > > + swappiness = 0; > > > + } > > > obviously this swappiness is neither /proc/sys/vm/swappiness nor > > > /sys/fs/cgroup/memory/<group>/>memory.swappiness, right? > > > > Right. > > > > > > @@ -3928,6 +4726,11 @@ static void age_active_anon(struct pglist_data *pgdat, > > > > struct mem_cgroup *memcg; > > > > struct lruvec *lruvec; > > > > > > > > + if (lru_gen_enabled()) { > > > > + lru_gen_age_node(pgdat, sc); > > > > + return; > > > > + } > > > > > > is it really a good place for lru_gen_age_node() since the function > > > is named age_active_anon() > > > but here you are doing aging for both anon and file pages? > > > > Yes. > > > > > obviously > > > lru_gen_age_node() is not > > > > doing "age active anon". > > > ;> We can rename it if you have something in mind. > > i wonder if we can directly do: > > if (lru_gen_enabled()) > lru_gen_age_node(pgdat, sc); > else > age_active_anon(); This looks good to me. I've queued it for the next version. Thanks.
On Thu, Apr 7, 2022 at 3:16 PM Yu Zhao <yuzhao@google.com> wrote: > > To avoid confusion, the terms "promotion" and "demotion" will be > applied to the multi-gen LRU, as a new convention; the terms > "activation" and "deactivation" will be applied to the active/inactive > LRU, as usual. > > The aging produces young generations. Given an lruvec, it increments > max_seq when max_seq-min_seq+1 approaches MIN_NR_GENS. The aging > promotes hot pages to the youngest generation when it finds them > accessed through page tables; the demotion of cold pages happens > consequently when it increments max_seq. The aging has the complexity > O(nr_hot_pages), since it is only interested in hot pages. Promotion > in the aging path does not require any LRU list operations, only the > updates of the gen counter and lrugen->nr_pages[]; demotion, unless as > the result of the increment of max_seq, requires LRU list operations, > e.g., lru_deactivate_fn(). > > The eviction consumes old generations. Given an lruvec, it increments > min_seq when the lists indexed by min_seq%MAX_NR_GENS become empty. A > feedback loop modeled after the PID controller monitors refaults over > anon and file types and decides which type to evict when both types > are available from the same generation. > > Each generation is divided into multiple tiers. Tiers represent > different ranges of numbers of accesses through file descriptors. A > page accessed N times through file descriptors is in tier > order_base_2(N). Tiers do not have dedicated lrugen->lists[], only > bits in folio->flags. In contrast to moving across generations, which > requires the LRU lock, moving across tiers only involves operations on > folio->flags. The feedback loop also monitors refaults over all tiers > and decides when to protect pages in which tiers (N>1), using the > first tier (N=0,1) as a baseline. The first tier contains single-use > unmapped clean pages, which are most likely the best choices. The > eviction moves a page to the next generation, i.e., min_seq+1, if the > feedback loop decides so. This approach has the following advantages: > 1. It removes the cost of activation in the buffered access path by > inferring whether pages accessed multiple times through file > descriptors are statistically hot and thus worth protecting in the > eviction path. > 2. It takes pages accessed through page tables into account and avoids > overprotecting pages accessed multiple times through file > descriptors. (Pages accessed through page tables are in the first > tier, since N=0.) > 3. More tiers provide better protection for pages accessed more than > twice through file descriptors, when under heavy buffered I/O > workloads. > Hi Yu, As I told you before, I tried to change the current LRU (not MGLRU) by only promoting unmapped file pages to the head of the inactive head rather than the active head on its second access: https://lore.kernel.org/lkml/CAGsJ_4y=TkCGoWWtWSAptW4RDFUEBeYXwfwu=fUFvV4Sa4VA4A@mail.gmail.com/ I have already seen some very good results by the decease of cpu consumption of kswapd and direct reclamation in the testing. in mglru, it seems "twice" isn't a concern at all, one unmapped file page accessed twice has no much difference with those ones which are accessed once as you only begin to increase refs from the third time: +static void folio_inc_refs(struct folio *folio) +{ + unsigned long refs; + unsigned long old_flags, new_flags; + + if (folio_test_unevictable(folio)) + return; + + /* see the comment on MAX_NR_TIERS */ + do { + new_flags = old_flags = READ_ONCE(folio->flags); + + if (!(new_flags & BIT(PG_referenced))) { + new_flags |= BIT(PG_referenced); + continue; + } + + if (!(new_flags & BIT(PG_workingset))) { + new_flags |= BIT(PG_workingset); + continue; + } + + refs = new_flags & LRU_REFS_MASK; + refs = min(refs + BIT(LRU_REFS_PGOFF), LRU_REFS_MASK); + + new_flags &= ~LRU_REFS_MASK; + new_flags |= refs; + } while (new_flags != old_flags && + cmpxchg(&folio->flags, old_flags, new_flags) != old_flags); +} So my question is what makes you so confident that twice doesn't need any special treatment while the vanilla kernel is upgrading this kind of page to the head of the active instead? I am asking this because I am considering reclaiming unmapped file pages which are only accessed twice when they get to the tail of the inactive list. Thanks Barry
On Mon, Apr 18, 2022 at 3:58 AM Barry Song <21cnbao@gmail.com> wrote: > > On Thu, Apr 7, 2022 at 3:16 PM Yu Zhao <yuzhao@google.com> wrote: > > > > To avoid confusion, the terms "promotion" and "demotion" will be > > applied to the multi-gen LRU, as a new convention; the terms > > "activation" and "deactivation" will be applied to the active/inactive > > LRU, as usual. > > > > The aging produces young generations. Given an lruvec, it increments > > max_seq when max_seq-min_seq+1 approaches MIN_NR_GENS. The aging > > promotes hot pages to the youngest generation when it finds them > > accessed through page tables; the demotion of cold pages happens > > consequently when it increments max_seq. The aging has the complexity > > O(nr_hot_pages), since it is only interested in hot pages. Promotion > > in the aging path does not require any LRU list operations, only the > > updates of the gen counter and lrugen->nr_pages[]; demotion, unless as > > the result of the increment of max_seq, requires LRU list operations, > > e.g., lru_deactivate_fn(). > > > > The eviction consumes old generations. Given an lruvec, it increments > > min_seq when the lists indexed by min_seq%MAX_NR_GENS become empty. A > > feedback loop modeled after the PID controller monitors refaults over > > anon and file types and decides which type to evict when both types > > are available from the same generation. > > > > Each generation is divided into multiple tiers. Tiers represent > > different ranges of numbers of accesses through file descriptors. A > > page accessed N times through file descriptors is in tier > > order_base_2(N). Tiers do not have dedicated lrugen->lists[], only > > bits in folio->flags. In contrast to moving across generations, which > > requires the LRU lock, moving across tiers only involves operations on > > folio->flags. The feedback loop also monitors refaults over all tiers > > and decides when to protect pages in which tiers (N>1), using the > > first tier (N=0,1) as a baseline. The first tier contains single-use > > unmapped clean pages, which are most likely the best choices. The > > eviction moves a page to the next generation, i.e., min_seq+1, if the > > feedback loop decides so. This approach has the following advantages: > > 1. It removes the cost of activation in the buffered access path by > > inferring whether pages accessed multiple times through file > > descriptors are statistically hot and thus worth protecting in the > > eviction path. > > 2. It takes pages accessed through page tables into account and avoids > > overprotecting pages accessed multiple times through file > > descriptors. (Pages accessed through page tables are in the first > > tier, since N=0.) > > 3. More tiers provide better protection for pages accessed more than > > twice through file descriptors, when under heavy buffered I/O > > workloads. > > > > Hi Yu, > As I told you before, I tried to change the current LRU (not MGLRU) by only > promoting unmapped file pages to the head of the inactive head rather than > the active head on its second access: > https://lore.kernel.org/lkml/CAGsJ_4y=TkCGoWWtWSAptW4RDFUEBeYXwfwu=fUFvV4Sa4VA4A@mail.gmail.com/ > I have already seen some very good results by the decease of cpu consumption of > kswapd and direct reclamation in the testing. Glad to hear. I suspected you'd see some good results with that change :) > in mglru, it seems "twice" isn't a concern at all, one unmapped file > page accessed > twice has no much difference with those ones which are accessed once as you > only begin to increase refs from the third time: refs are *additional* accesses: PG_referenced: N=1 PG_referenced+PG_workingset: N=2 PG_referenced+PG_workingset+refs: N=3,4,5 When N=2, order_base_2(N)=1. So pages accessed twice are in the second tier. Therefore they are "different". More details [1]: +/* + * Each generation is divided into multiple tiers. Tiers represent different + * ranges of numbers of accesses through file descriptors. A page accessed N + * times through file descriptors is in tier order_base_2(N). A page in the + * first tier (N=0,1) is marked by PG_referenced unless it was faulted in + * though page tables or read ahead. A page in any other tier (N>1) is marked + * by PG_referenced and PG_workingset. + * + * In contrast to moving across generations which requires the LRU lock, moving + * across tiers only requires operations on folio->flags and therefore has a + * negligible cost in the buffered access path. In the eviction path, + * comparisons of refaulted/(evicted+protected) from the first tier and the + * rest infer whether pages accessed multiple times through file descriptors + * are statistically hot and thus worth protecting. + * + * MAX_NR_TIERS is set to 4 so that the multi-gen LRU can support twice of the + * categories of the active/inactive LRU when keeping track of accesses through + * file descriptors. It requires MAX_NR_TIERS-2 additional bits in folio->flags. + */ +#define MAX_NR_TIERS 4U [1] https://lore.kernel.org/linux-mm/20220407031525.2368067-7-yuzhao@google.com/ > +static void folio_inc_refs(struct folio *folio) > +{ > + unsigned long refs; > + unsigned long old_flags, new_flags; > + > + if (folio_test_unevictable(folio)) > + return; > + > + /* see the comment on MAX_NR_TIERS */ > + do { > + new_flags = old_flags = READ_ONCE(folio->flags); > + > + if (!(new_flags & BIT(PG_referenced))) { > + new_flags |= BIT(PG_referenced); > + continue; > + } > + > + if (!(new_flags & BIT(PG_workingset))) { > + new_flags |= BIT(PG_workingset); > + continue; > + } > + > + refs = new_flags & LRU_REFS_MASK; > + refs = min(refs + BIT(LRU_REFS_PGOFF), LRU_REFS_MASK); > + > + new_flags &= ~LRU_REFS_MASK; > + new_flags |= refs; > + } while (new_flags != old_flags && > + cmpxchg(&folio->flags, old_flags, new_flags) != old_flags); > +} > > So my question is what makes you so confident that twice doesn't need > any special treatment while the vanilla kernel is upgrading this kind of page > to the head of the active instead? I am asking this because I am considering > reclaiming unmapped file pages which are only accessed twice when they > get to the tail of the inactive list. Per above, pages accessed twice are in their own tier. Hope this clarifies it.
On Tue, Apr 19, 2022 at 12:54 PM Yu Zhao <yuzhao@google.com> wrote: > > On Mon, Apr 18, 2022 at 3:58 AM Barry Song <21cnbao@gmail.com> wrote: > > > > On Thu, Apr 7, 2022 at 3:16 PM Yu Zhao <yuzhao@google.com> wrote: > > > > > > To avoid confusion, the terms "promotion" and "demotion" will be > > > applied to the multi-gen LRU, as a new convention; the terms > > > "activation" and "deactivation" will be applied to the active/inactive > > > LRU, as usual. > > > > > > The aging produces young generations. Given an lruvec, it increments > > > max_seq when max_seq-min_seq+1 approaches MIN_NR_GENS. The aging > > > promotes hot pages to the youngest generation when it finds them > > > accessed through page tables; the demotion of cold pages happens > > > consequently when it increments max_seq. The aging has the complexity > > > O(nr_hot_pages), since it is only interested in hot pages. Promotion > > > in the aging path does not require any LRU list operations, only the > > > updates of the gen counter and lrugen->nr_pages[]; demotion, unless as > > > the result of the increment of max_seq, requires LRU list operations, > > > e.g., lru_deactivate_fn(). > > > > > > The eviction consumes old generations. Given an lruvec, it increments > > > min_seq when the lists indexed by min_seq%MAX_NR_GENS become empty. A > > > feedback loop modeled after the PID controller monitors refaults over > > > anon and file types and decides which type to evict when both types > > > are available from the same generation. > > > > > > Each generation is divided into multiple tiers. Tiers represent > > > different ranges of numbers of accesses through file descriptors. A > > > page accessed N times through file descriptors is in tier > > > order_base_2(N). Tiers do not have dedicated lrugen->lists[], only > > > bits in folio->flags. In contrast to moving across generations, which > > > requires the LRU lock, moving across tiers only involves operations on > > > folio->flags. The feedback loop also monitors refaults over all tiers > > > and decides when to protect pages in which tiers (N>1), using the > > > first tier (N=0,1) as a baseline. The first tier contains single-use > > > unmapped clean pages, which are most likely the best choices. The > > > eviction moves a page to the next generation, i.e., min_seq+1, if the > > > feedback loop decides so. This approach has the following advantages: > > > 1. It removes the cost of activation in the buffered access path by > > > inferring whether pages accessed multiple times through file > > > descriptors are statistically hot and thus worth protecting in the > > > eviction path. > > > 2. It takes pages accessed through page tables into account and avoids > > > overprotecting pages accessed multiple times through file > > > descriptors. (Pages accessed through page tables are in the first > > > tier, since N=0.) > > > 3. More tiers provide better protection for pages accessed more than > > > twice through file descriptors, when under heavy buffered I/O > > > workloads. > > > > > > > Hi Yu, > > As I told you before, I tried to change the current LRU (not MGLRU) by only > > promoting unmapped file pages to the head of the inactive head rather than > > the active head on its second access: > > https://lore.kernel.org/lkml/CAGsJ_4y=TkCGoWWtWSAptW4RDFUEBeYXwfwu=fUFvV4Sa4VA4A@mail.gmail.com/ > > I have already seen some very good results by the decease of cpu consumption of > > kswapd and direct reclamation in the testing. > > Glad to hear. I suspected you'd see some good results with that change :) > > > in mglru, it seems "twice" isn't a concern at all, one unmapped file > > page accessed > > twice has no much difference with those ones which are accessed once as you > > only begin to increase refs from the third time: > > refs are *additional* accesses: > PG_referenced: N=1 > PG_referenced+PG_workingset: N=2 > PG_referenced+PG_workingset+refs: N=3,4,5 > > When N=2, order_base_2(N)=1. So pages accessed twice are in the second > tier. Therefore they are "different". > > More details [1]: > > +/* > + * Each generation is divided into multiple tiers. Tiers represent different > + * ranges of numbers of accesses through file descriptors. A page accessed N > + * times through file descriptors is in tier order_base_2(N). A page in the > + * first tier (N=0,1) is marked by PG_referenced unless it was faulted in > + * though page tables or read ahead. A page in any other tier (N>1) is marked > + * by PG_referenced and PG_workingset. > + * > + * In contrast to moving across generations which requires the LRU lock, moving > + * across tiers only requires operations on folio->flags and therefore has a > + * negligible cost in the buffered access path. In the eviction path, > + * comparisons of refaulted/(evicted+protected) from the first tier and the > + * rest infer whether pages accessed multiple times through file descriptors > + * are statistically hot and thus worth protecting. > + * > + * MAX_NR_TIERS is set to 4 so that the multi-gen LRU can support twice of the > + * categories of the active/inactive LRU when keeping track of accesses through > + * file descriptors. It requires MAX_NR_TIERS-2 additional bits in > folio->flags. > + */ > +#define MAX_NR_TIERS 4U > > [1] https://lore.kernel.org/linux-mm/20220407031525.2368067-7-yuzhao@google.com/ > > > +static void folio_inc_refs(struct folio *folio) > > +{ > > + unsigned long refs; > > + unsigned long old_flags, new_flags; > > + > > + if (folio_test_unevictable(folio)) > > + return; > > + > > + /* see the comment on MAX_NR_TIERS */ > > + do { > > + new_flags = old_flags = READ_ONCE(folio->flags); > > + > > + if (!(new_flags & BIT(PG_referenced))) { > > + new_flags |= BIT(PG_referenced); > > + continue; > > + } > > + > > + if (!(new_flags & BIT(PG_workingset))) { > > + new_flags |= BIT(PG_workingset); > > + continue; > > + } > > + > > + refs = new_flags & LRU_REFS_MASK; > > + refs = min(refs + BIT(LRU_REFS_PGOFF), LRU_REFS_MASK); > > + > > + new_flags &= ~LRU_REFS_MASK; > > + new_flags |= refs; > > + } while (new_flags != old_flags && > > + cmpxchg(&folio->flags, old_flags, new_flags) != old_flags); > > +} > > > > So my question is what makes you so confident that twice doesn't need > > any special treatment while the vanilla kernel is upgrading this kind of page > > to the head of the active instead? I am asking this because I am considering > > reclaiming unmapped file pages which are only accessed twice when they > > get to the tail of the inactive list. > > Per above, pages accessed twice are in their own tier. Hope this clarifies it. Yep, I found the trick here , "+1" is magic behind the code, haha. +static int folio_lru_tier(struct folio *folio) +{ + int refs; + unsigned long flags = READ_ONCE(folio->flags); + + refs = (flags & LRU_REFS_FLAGS) == LRU_REFS_FLAGS ? + ((flags & LRU_REFS_MASK) >> LRU_REFS_PGOFF) + 1 : 0; + + return lru_tier_from_refs(refs); +} + TBH, this might need some comments, otherwise, it is easy to misunderstand we are beginning to have protection from 3rd access :-) Thanks barry
On Tue, Apr 19, 2022 at 4:25 PM Barry Song <21cnbao@gmail.com> wrote: > > On Tue, Apr 19, 2022 at 12:54 PM Yu Zhao <yuzhao@google.com> wrote: > > > > On Mon, Apr 18, 2022 at 3:58 AM Barry Song <21cnbao@gmail.com> wrote: > > > > > > On Thu, Apr 7, 2022 at 3:16 PM Yu Zhao <yuzhao@google.com> wrote: > > > > > > > > To avoid confusion, the terms "promotion" and "demotion" will be > > > > applied to the multi-gen LRU, as a new convention; the terms > > > > "activation" and "deactivation" will be applied to the active/inactive > > > > LRU, as usual. > > > > > > > > The aging produces young generations. Given an lruvec, it increments > > > > max_seq when max_seq-min_seq+1 approaches MIN_NR_GENS. The aging > > > > promotes hot pages to the youngest generation when it finds them > > > > accessed through page tables; the demotion of cold pages happens > > > > consequently when it increments max_seq. The aging has the complexity > > > > O(nr_hot_pages), since it is only interested in hot pages. Promotion > > > > in the aging path does not require any LRU list operations, only the > > > > updates of the gen counter and lrugen->nr_pages[]; demotion, unless as > > > > the result of the increment of max_seq, requires LRU list operations, > > > > e.g., lru_deactivate_fn(). > > > > > > > > The eviction consumes old generations. Given an lruvec, it increments > > > > min_seq when the lists indexed by min_seq%MAX_NR_GENS become empty. A > > > > feedback loop modeled after the PID controller monitors refaults over > > > > anon and file types and decides which type to evict when both types > > > > are available from the same generation. > > > > > > > > Each generation is divided into multiple tiers. Tiers represent > > > > different ranges of numbers of accesses through file descriptors. A > > > > page accessed N times through file descriptors is in tier > > > > order_base_2(N). Tiers do not have dedicated lrugen->lists[], only > > > > bits in folio->flags. In contrast to moving across generations, which > > > > requires the LRU lock, moving across tiers only involves operations on > > > > folio->flags. The feedback loop also monitors refaults over all tiers > > > > and decides when to protect pages in which tiers (N>1), using the > > > > first tier (N=0,1) as a baseline. The first tier contains single-use > > > > unmapped clean pages, which are most likely the best choices. The > > > > eviction moves a page to the next generation, i.e., min_seq+1, if the > > > > feedback loop decides so. This approach has the following advantages: > > > > 1. It removes the cost of activation in the buffered access path by > > > > inferring whether pages accessed multiple times through file > > > > descriptors are statistically hot and thus worth protecting in the > > > > eviction path. > > > > 2. It takes pages accessed through page tables into account and avoids > > > > overprotecting pages accessed multiple times through file > > > > descriptors. (Pages accessed through page tables are in the first > > > > tier, since N=0.) > > > > 3. More tiers provide better protection for pages accessed more than > > > > twice through file descriptors, when under heavy buffered I/O > > > > workloads. > > > > > > > > > > Hi Yu, > > > As I told you before, I tried to change the current LRU (not MGLRU) by only > > > promoting unmapped file pages to the head of the inactive head rather than > > > the active head on its second access: > > > https://lore.kernel.org/lkml/CAGsJ_4y=TkCGoWWtWSAptW4RDFUEBeYXwfwu=fUFvV4Sa4VA4A@mail.gmail.com/ > > > I have already seen some very good results by the decease of cpu consumption of > > > kswapd and direct reclamation in the testing. > > > > Glad to hear. I suspected you'd see some good results with that change :) > > > > > in mglru, it seems "twice" isn't a concern at all, one unmapped file > > > page accessed > > > twice has no much difference with those ones which are accessed once as you > > > only begin to increase refs from the third time: > > > > refs are *additional* accesses: > > PG_referenced: N=1 > > PG_referenced+PG_workingset: N=2 > > PG_referenced+PG_workingset+refs: N=3,4,5 > > > > When N=2, order_base_2(N)=1. So pages accessed twice are in the second > > tier. Therefore they are "different". > > > > More details [1]: > > > > +/* > > + * Each generation is divided into multiple tiers. Tiers represent different > > + * ranges of numbers of accesses through file descriptors. A page accessed N > > + * times through file descriptors is in tier order_base_2(N). A page in the > > + * first tier (N=0,1) is marked by PG_referenced unless it was faulted in > > + * though page tables or read ahead. A page in any other tier (N>1) is marked > > + * by PG_referenced and PG_workingset. > > + * > > + * In contrast to moving across generations which requires the LRU lock, moving > > + * across tiers only requires operations on folio->flags and therefore has a > > + * negligible cost in the buffered access path. In the eviction path, > > + * comparisons of refaulted/(evicted+protected) from the first tier and the > > + * rest infer whether pages accessed multiple times through file descriptors > > + * are statistically hot and thus worth protecting. > > + * > > + * MAX_NR_TIERS is set to 4 so that the multi-gen LRU can support twice of the > > + * categories of the active/inactive LRU when keeping track of accesses through > > + * file descriptors. It requires MAX_NR_TIERS-2 additional bits in > > folio->flags. > > + */ > > +#define MAX_NR_TIERS 4U > > > > [1] https://lore.kernel.org/linux-mm/20220407031525.2368067-7-yuzhao@google.com/ > > > > > +static void folio_inc_refs(struct folio *folio) > > > +{ > > > + unsigned long refs; > > > + unsigned long old_flags, new_flags; > > > + > > > + if (folio_test_unevictable(folio)) > > > + return; > > > + > > > + /* see the comment on MAX_NR_TIERS */ > > > + do { > > > + new_flags = old_flags = READ_ONCE(folio->flags); > > > + > > > + if (!(new_flags & BIT(PG_referenced))) { > > > + new_flags |= BIT(PG_referenced); > > > + continue; > > > + } > > > + > > > + if (!(new_flags & BIT(PG_workingset))) { > > > + new_flags |= BIT(PG_workingset); > > > + continue; > > > + } > > > + > > > + refs = new_flags & LRU_REFS_MASK; > > > + refs = min(refs + BIT(LRU_REFS_PGOFF), LRU_REFS_MASK); > > > + > > > + new_flags &= ~LRU_REFS_MASK; > > > + new_flags |= refs; > > > + } while (new_flags != old_flags && > > > + cmpxchg(&folio->flags, old_flags, new_flags) != old_flags); > > > +} > > > > > > So my question is what makes you so confident that twice doesn't need > > > any special treatment while the vanilla kernel is upgrading this kind of page > > > to the head of the active instead? I am asking this because I am considering > > > reclaiming unmapped file pages which are only accessed twice when they > > > get to the tail of the inactive list. > > > > Per above, pages accessed twice are in their own tier. Hope this clarifies it. > > Yep, I found the trick here , "+1" is magic behind the code, haha. > > +static int folio_lru_tier(struct folio *folio) > +{ > + int refs; > + unsigned long flags = READ_ONCE(folio->flags); > + > + refs = (flags & LRU_REFS_FLAGS) == LRU_REFS_FLAGS ? > + ((flags & LRU_REFS_MASK) >> LRU_REFS_PGOFF) + 1 : 0; > + > + return lru_tier_from_refs(refs); > +} > + > > TBH, this might need some comments, otherwise, it is easy to misunderstand > we are beginning to have protection from 3rd access :-) as anyway, it would be much more straightforward to have the below if we can also increase refs for the 1st and 2nd access in folio_inc_refs(): +static int folio_lru_tier(struct folio *folio) +{ + int refs; + unsigned long flags = READ_ONCE(folio->flags); + + refs = (flags & LRU_REFS_MASK) >> LRU_REFS_PGOFF; + + return lru_tier_from_refs(refs); +} Thanks Barry
On Mon, Apr 18, 2022 at 10:26 PM Barry Song <21cnbao@gmail.com> wrote: > > On Tue, Apr 19, 2022 at 12:54 PM Yu Zhao <yuzhao@google.com> wrote: > > > > On Mon, Apr 18, 2022 at 3:58 AM Barry Song <21cnbao@gmail.com> wrote: > > > > > > On Thu, Apr 7, 2022 at 3:16 PM Yu Zhao <yuzhao@google.com> wrote: > > > > > > > > To avoid confusion, the terms "promotion" and "demotion" will be > > > > applied to the multi-gen LRU, as a new convention; the terms > > > > "activation" and "deactivation" will be applied to the active/inactive > > > > LRU, as usual. > > > > > > > > The aging produces young generations. Given an lruvec, it increments > > > > max_seq when max_seq-min_seq+1 approaches MIN_NR_GENS. The aging > > > > promotes hot pages to the youngest generation when it finds them > > > > accessed through page tables; the demotion of cold pages happens > > > > consequently when it increments max_seq. The aging has the complexity > > > > O(nr_hot_pages), since it is only interested in hot pages. Promotion > > > > in the aging path does not require any LRU list operations, only the > > > > updates of the gen counter and lrugen->nr_pages[]; demotion, unless as > > > > the result of the increment of max_seq, requires LRU list operations, > > > > e.g., lru_deactivate_fn(). > > > > > > > > The eviction consumes old generations. Given an lruvec, it increments > > > > min_seq when the lists indexed by min_seq%MAX_NR_GENS become empty. A > > > > feedback loop modeled after the PID controller monitors refaults over > > > > anon and file types and decides which type to evict when both types > > > > are available from the same generation. > > > > > > > > Each generation is divided into multiple tiers. Tiers represent > > > > different ranges of numbers of accesses through file descriptors. A > > > > page accessed N times through file descriptors is in tier > > > > order_base_2(N). Tiers do not have dedicated lrugen->lists[], only > > > > bits in folio->flags. In contrast to moving across generations, which > > > > requires the LRU lock, moving across tiers only involves operations on > > > > folio->flags. The feedback loop also monitors refaults over all tiers > > > > and decides when to protect pages in which tiers (N>1), using the > > > > first tier (N=0,1) as a baseline. The first tier contains single-use > > > > unmapped clean pages, which are most likely the best choices. The > > > > eviction moves a page to the next generation, i.e., min_seq+1, if the > > > > feedback loop decides so. This approach has the following advantages: > > > > 1. It removes the cost of activation in the buffered access path by > > > > inferring whether pages accessed multiple times through file > > > > descriptors are statistically hot and thus worth protecting in the > > > > eviction path. > > > > 2. It takes pages accessed through page tables into account and avoids > > > > overprotecting pages accessed multiple times through file > > > > descriptors. (Pages accessed through page tables are in the first > > > > tier, since N=0.) > > > > 3. More tiers provide better protection for pages accessed more than > > > > twice through file descriptors, when under heavy buffered I/O > > > > workloads. > > > > > > > > > > Hi Yu, > > > As I told you before, I tried to change the current LRU (not MGLRU) by only > > > promoting unmapped file pages to the head of the inactive head rather than > > > the active head on its second access: > > > https://lore.kernel.org/lkml/CAGsJ_4y=TkCGoWWtWSAptW4RDFUEBeYXwfwu=fUFvV4Sa4VA4A@mail.gmail.com/ > > > I have already seen some very good results by the decease of cpu consumption of > > > kswapd and direct reclamation in the testing. > > > > Glad to hear. I suspected you'd see some good results with that change :) > > > > > in mglru, it seems "twice" isn't a concern at all, one unmapped file > > > page accessed > > > twice has no much difference with those ones which are accessed once as you > > > only begin to increase refs from the third time: > > > > refs are *additional* accesses: > > PG_referenced: N=1 > > PG_referenced+PG_workingset: N=2 > > PG_referenced+PG_workingset+refs: N=3,4,5 > > > > When N=2, order_base_2(N)=1. So pages accessed twice are in the second > > tier. Therefore they are "different". > > > > More details [1]: > > > > +/* > > + * Each generation is divided into multiple tiers. Tiers represent different > > + * ranges of numbers of accesses through file descriptors. A page accessed N > > + * times through file descriptors is in tier order_base_2(N). A page in the > > + * first tier (N=0,1) is marked by PG_referenced unless it was faulted in > > + * though page tables or read ahead. A page in any other tier (N>1) is marked > > + * by PG_referenced and PG_workingset. > > + * > > + * In contrast to moving across generations which requires the LRU lock, moving > > + * across tiers only requires operations on folio->flags and therefore has a > > + * negligible cost in the buffered access path. In the eviction path, > > + * comparisons of refaulted/(evicted+protected) from the first tier and the > > + * rest infer whether pages accessed multiple times through file descriptors > > + * are statistically hot and thus worth protecting. > > + * > > + * MAX_NR_TIERS is set to 4 so that the multi-gen LRU can support twice of the > > + * categories of the active/inactive LRU when keeping track of accesses through > > + * file descriptors. It requires MAX_NR_TIERS-2 additional bits in > > folio->flags. > > + */ > > +#define MAX_NR_TIERS 4U > > > > [1] https://lore.kernel.org/linux-mm/20220407031525.2368067-7-yuzhao@google.com/ > > > > > +static void folio_inc_refs(struct folio *folio) > > > +{ > > > + unsigned long refs; > > > + unsigned long old_flags, new_flags; > > > + > > > + if (folio_test_unevictable(folio)) > > > + return; > > > + > > > + /* see the comment on MAX_NR_TIERS */ > > > + do { > > > + new_flags = old_flags = READ_ONCE(folio->flags); > > > + > > > + if (!(new_flags & BIT(PG_referenced))) { > > > + new_flags |= BIT(PG_referenced); > > > + continue; > > > + } > > > + > > > + if (!(new_flags & BIT(PG_workingset))) { > > > + new_flags |= BIT(PG_workingset); > > > + continue; > > > + } > > > + > > > + refs = new_flags & LRU_REFS_MASK; > > > + refs = min(refs + BIT(LRU_REFS_PGOFF), LRU_REFS_MASK); > > > + > > > + new_flags &= ~LRU_REFS_MASK; > > > + new_flags |= refs; > > > + } while (new_flags != old_flags && > > > + cmpxchg(&folio->flags, old_flags, new_flags) != old_flags); > > > +} > > > > > > So my question is what makes you so confident that twice doesn't need > > > any special treatment while the vanilla kernel is upgrading this kind of page > > > to the head of the active instead? I am asking this because I am considering > > > reclaiming unmapped file pages which are only accessed twice when they > > > get to the tail of the inactive list. > > > > Per above, pages accessed twice are in their own tier. Hope this clarifies it. > > Yep, I found the trick here , "+1" is magic behind the code, haha. > > +static int folio_lru_tier(struct folio *folio) > +{ > + int refs; > + unsigned long flags = READ_ONCE(folio->flags); > + > + refs = (flags & LRU_REFS_FLAGS) == LRU_REFS_FLAGS ? > + ((flags & LRU_REFS_MASK) >> LRU_REFS_PGOFF) + 1 : 0; > + > + return lru_tier_from_refs(refs); > +} > + > > TBH, this might need some comments, otherwise, it is easy to misunderstand > we are beginning to have protection from 3rd access :-) Agreed. Let me rework this function. I don't know how yet but I'll think of something.
On Mon, Apr 18, 2022 at 10:36 PM Barry Song <21cnbao@gmail.com> wrote: > > On Tue, Apr 19, 2022 at 4:25 PM Barry Song <21cnbao@gmail.com> wrote: > > > > On Tue, Apr 19, 2022 at 12:54 PM Yu Zhao <yuzhao@google.com> wrote: > > > > > > On Mon, Apr 18, 2022 at 3:58 AM Barry Song <21cnbao@gmail.com> wrote: > > > > > > > > On Thu, Apr 7, 2022 at 3:16 PM Yu Zhao <yuzhao@google.com> wrote: > > > > > > > > > > To avoid confusion, the terms "promotion" and "demotion" will be > > > > > applied to the multi-gen LRU, as a new convention; the terms > > > > > "activation" and "deactivation" will be applied to the active/inactive > > > > > LRU, as usual. > > > > > > > > > > The aging produces young generations. Given an lruvec, it increments > > > > > max_seq when max_seq-min_seq+1 approaches MIN_NR_GENS. The aging > > > > > promotes hot pages to the youngest generation when it finds them > > > > > accessed through page tables; the demotion of cold pages happens > > > > > consequently when it increments max_seq. The aging has the complexity > > > > > O(nr_hot_pages), since it is only interested in hot pages. Promotion > > > > > in the aging path does not require any LRU list operations, only the > > > > > updates of the gen counter and lrugen->nr_pages[]; demotion, unless as > > > > > the result of the increment of max_seq, requires LRU list operations, > > > > > e.g., lru_deactivate_fn(). > > > > > > > > > > The eviction consumes old generations. Given an lruvec, it increments > > > > > min_seq when the lists indexed by min_seq%MAX_NR_GENS become empty. A > > > > > feedback loop modeled after the PID controller monitors refaults over > > > > > anon and file types and decides which type to evict when both types > > > > > are available from the same generation. > > > > > > > > > > Each generation is divided into multiple tiers. Tiers represent > > > > > different ranges of numbers of accesses through file descriptors. A > > > > > page accessed N times through file descriptors is in tier > > > > > order_base_2(N). Tiers do not have dedicated lrugen->lists[], only > > > > > bits in folio->flags. In contrast to moving across generations, which > > > > > requires the LRU lock, moving across tiers only involves operations on > > > > > folio->flags. The feedback loop also monitors refaults over all tiers > > > > > and decides when to protect pages in which tiers (N>1), using the > > > > > first tier (N=0,1) as a baseline. The first tier contains single-use > > > > > unmapped clean pages, which are most likely the best choices. The > > > > > eviction moves a page to the next generation, i.e., min_seq+1, if the > > > > > feedback loop decides so. This approach has the following advantages: > > > > > 1. It removes the cost of activation in the buffered access path by > > > > > inferring whether pages accessed multiple times through file > > > > > descriptors are statistically hot and thus worth protecting in the > > > > > eviction path. > > > > > 2. It takes pages accessed through page tables into account and avoids > > > > > overprotecting pages accessed multiple times through file > > > > > descriptors. (Pages accessed through page tables are in the first > > > > > tier, since N=0.) > > > > > 3. More tiers provide better protection for pages accessed more than > > > > > twice through file descriptors, when under heavy buffered I/O > > > > > workloads. > > > > > > > > > > > > > Hi Yu, > > > > As I told you before, I tried to change the current LRU (not MGLRU) by only > > > > promoting unmapped file pages to the head of the inactive head rather than > > > > the active head on its second access: > > > > https://lore.kernel.org/lkml/CAGsJ_4y=TkCGoWWtWSAptW4RDFUEBeYXwfwu=fUFvV4Sa4VA4A@mail.gmail.com/ > > > > I have already seen some very good results by the decease of cpu consumption of > > > > kswapd and direct reclamation in the testing. > > > > > > Glad to hear. I suspected you'd see some good results with that change :) > > > > > > > in mglru, it seems "twice" isn't a concern at all, one unmapped file > > > > page accessed > > > > twice has no much difference with those ones which are accessed once as you > > > > only begin to increase refs from the third time: > > > > > > refs are *additional* accesses: > > > PG_referenced: N=1 > > > PG_referenced+PG_workingset: N=2 > > > PG_referenced+PG_workingset+refs: N=3,4,5 > > > > > > When N=2, order_base_2(N)=1. So pages accessed twice are in the second > > > tier. Therefore they are "different". > > > > > > More details [1]: > > > > > > +/* > > > + * Each generation is divided into multiple tiers. Tiers represent different > > > + * ranges of numbers of accesses through file descriptors. A page accessed N > > > + * times through file descriptors is in tier order_base_2(N). A page in the > > > + * first tier (N=0,1) is marked by PG_referenced unless it was faulted in > > > + * though page tables or read ahead. A page in any other tier (N>1) is marked > > > + * by PG_referenced and PG_workingset. > > > + * > > > + * In contrast to moving across generations which requires the LRU lock, moving > > > + * across tiers only requires operations on folio->flags and therefore has a > > > + * negligible cost in the buffered access path. In the eviction path, > > > + * comparisons of refaulted/(evicted+protected) from the first tier and the > > > + * rest infer whether pages accessed multiple times through file descriptors > > > + * are statistically hot and thus worth protecting. > > > + * > > > + * MAX_NR_TIERS is set to 4 so that the multi-gen LRU can support twice of the > > > + * categories of the active/inactive LRU when keeping track of accesses through > > > + * file descriptors. It requires MAX_NR_TIERS-2 additional bits in > > > folio->flags. > > > + */ > > > +#define MAX_NR_TIERS 4U > > > > > > [1] https://lore.kernel.org/linux-mm/20220407031525.2368067-7-yuzhao@google.com/ > > > > > > > +static void folio_inc_refs(struct folio *folio) > > > > +{ > > > > + unsigned long refs; > > > > + unsigned long old_flags, new_flags; > > > > + > > > > + if (folio_test_unevictable(folio)) > > > > + return; > > > > + > > > > + /* see the comment on MAX_NR_TIERS */ > > > > + do { > > > > + new_flags = old_flags = READ_ONCE(folio->flags); > > > > + > > > > + if (!(new_flags & BIT(PG_referenced))) { > > > > + new_flags |= BIT(PG_referenced); > > > > + continue; > > > > + } > > > > + > > > > + if (!(new_flags & BIT(PG_workingset))) { > > > > + new_flags |= BIT(PG_workingset); > > > > + continue; > > > > + } > > > > + > > > > + refs = new_flags & LRU_REFS_MASK; > > > > + refs = min(refs + BIT(LRU_REFS_PGOFF), LRU_REFS_MASK); > > > > + > > > > + new_flags &= ~LRU_REFS_MASK; > > > > + new_flags |= refs; > > > > + } while (new_flags != old_flags && > > > > + cmpxchg(&folio->flags, old_flags, new_flags) != old_flags); > > > > +} > > > > > > > > So my question is what makes you so confident that twice doesn't need > > > > any special treatment while the vanilla kernel is upgrading this kind of page > > > > to the head of the active instead? I am asking this because I am considering > > > > reclaiming unmapped file pages which are only accessed twice when they > > > > get to the tail of the inactive list. > > > > > > Per above, pages accessed twice are in their own tier. Hope this clarifies it. > > > > Yep, I found the trick here , "+1" is magic behind the code, haha. > > > > +static int folio_lru_tier(struct folio *folio) > > +{ > > + int refs; > > + unsigned long flags = READ_ONCE(folio->flags); > > + > > + refs = (flags & LRU_REFS_FLAGS) == LRU_REFS_FLAGS ? > > + ((flags & LRU_REFS_MASK) >> LRU_REFS_PGOFF) + 1 : 0; > > + > > + return lru_tier_from_refs(refs); > > +} > > + > > > > TBH, this might need some comments, otherwise, it is easy to misunderstand > > we are beginning to have protection from 3rd access :-) > > as anyway, it would be much more straightforward to have the below if > we can also > increase refs for the 1st and 2nd access in folio_inc_refs(): It would if there were abundant spare bits in page->flags. On some machines, we don't, so we have to reuse PG_referenced and PG_workingset. > +static int folio_lru_tier(struct folio *folio) > +{ > + int refs; > + unsigned long flags = READ_ONCE(folio->flags); > + > + refs = (flags & LRU_REFS_MASK) >> LRU_REFS_PGOFF; > + > + return lru_tier_from_refs(refs); > +}
diff --git a/include/linux/mm_inline.h b/include/linux/mm_inline.h index 9abd72a95462..8a8f87b72540 100644 --- a/include/linux/mm_inline.h +++ b/include/linux/mm_inline.h @@ -119,6 +119,19 @@ static inline int lru_gen_from_seq(unsigned long seq) return seq % MAX_NR_GENS; } +static inline int lru_hist_from_seq(unsigned long seq) +{ + return seq % NR_HIST_GENS; +} + +static inline int lru_tier_from_refs(int refs) +{ + VM_BUG_ON(refs > BIT(LRU_REFS_WIDTH)); + + /* see the comment on MAX_NR_TIERS */ + return order_base_2(refs + 1); +} + static inline bool lru_gen_is_active(struct lruvec *lruvec, int gen) { unsigned long max_seq = lruvec->lrugen.max_seq; @@ -164,6 +177,15 @@ static inline void lru_gen_update_size(struct lruvec *lruvec, struct folio *foli __update_lru_size(lruvec, lru, zone, -delta); return; } + + /* promotion */ + if (!lru_gen_is_active(lruvec, old_gen) && lru_gen_is_active(lruvec, new_gen)) { + __update_lru_size(lruvec, lru, zone, -delta); + __update_lru_size(lruvec, lru + LRU_ACTIVE, zone, delta); + } + + /* demotion requires isolation, e.g., lru_deactivate_fn() */ + VM_BUG_ON(lru_gen_is_active(lruvec, old_gen) && !lru_gen_is_active(lruvec, new_gen)); } static inline bool lru_gen_add_folio(struct lruvec *lruvec, struct folio *folio, bool reclaiming) @@ -229,6 +251,8 @@ static inline bool lru_gen_del_folio(struct lruvec *lruvec, struct folio *folio, gen = ((new_flags & LRU_GEN_MASK) >> LRU_GEN_PGOFF) - 1; new_flags &= ~LRU_GEN_MASK; + if (!(new_flags & BIT(PG_referenced))) + new_flags &= ~(LRU_REFS_MASK | LRU_REFS_FLAGS); /* for shrink_page_list() */ if (reclaiming) new_flags &= ~(BIT(PG_referenced) | BIT(PG_reclaim)); diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h index bde05427e2bb..c8a7ceee7a0a 100644 --- a/include/linux/mmzone.h +++ b/include/linux/mmzone.h @@ -347,12 +347,34 @@ enum lruvec_flags { #define MIN_NR_GENS 2U #define MAX_NR_GENS 4U +/* + * Each generation is divided into multiple tiers. Tiers represent different + * ranges of numbers of accesses through file descriptors. A page accessed N + * times through file descriptors is in tier order_base_2(N). A page in the + * first tier (N=0,1) is marked by PG_referenced unless it was faulted in + * though page tables or read ahead. A page in any other tier (N>1) is marked + * by PG_referenced and PG_workingset. + * + * In contrast to moving across generations which requires the LRU lock, moving + * across tiers only requires operations on folio->flags and therefore has a + * negligible cost in the buffered access path. In the eviction path, + * comparisons of refaulted/(evicted+protected) from the first tier and the + * rest infer whether pages accessed multiple times through file descriptors + * are statistically hot and thus worth protecting. + * + * MAX_NR_TIERS is set to 4 so that the multi-gen LRU can support twice of the + * categories of the active/inactive LRU when keeping track of accesses through + * file descriptors. It requires MAX_NR_TIERS-2 additional bits in folio->flags. + */ +#define MAX_NR_TIERS 4U + #ifndef __GENERATING_BOUNDS_H struct lruvec; #define LRU_GEN_MASK ((BIT(LRU_GEN_WIDTH) - 1) << LRU_GEN_PGOFF) #define LRU_REFS_MASK ((BIT(LRU_REFS_WIDTH) - 1) << LRU_REFS_PGOFF) +#define LRU_REFS_FLAGS (BIT(PG_referenced) | BIT(PG_workingset)) #ifdef CONFIG_LRU_GEN @@ -361,6 +383,16 @@ enum { LRU_GEN_FILE, }; +#define MIN_LRU_BATCH BITS_PER_LONG +#define MAX_LRU_BATCH (MIN_LRU_BATCH * 128) + +/* whether to keep historical stats from evicted generations */ +#ifdef CONFIG_LRU_GEN_STATS +#define NR_HIST_GENS MAX_NR_GENS +#else +#define NR_HIST_GENS 1U +#endif + /* * The youngest generation number is stored in max_seq for both anon and file * types as they are aged on an equal footing. The oldest generation numbers are @@ -380,6 +412,15 @@ struct lru_gen_struct { struct list_head lists[MAX_NR_GENS][ANON_AND_FILE][MAX_NR_ZONES]; /* the sizes of the above lists */ unsigned long nr_pages[MAX_NR_GENS][ANON_AND_FILE][MAX_NR_ZONES]; + /* the exponential moving average of refaulted */ + unsigned long avg_refaulted[ANON_AND_FILE][MAX_NR_TIERS]; + /* the exponential moving average of evicted+protected */ + unsigned long avg_total[ANON_AND_FILE][MAX_NR_TIERS]; + /* the first tier doesn't need protection, hence the minus one */ + unsigned long protected[NR_HIST_GENS][ANON_AND_FILE][MAX_NR_TIERS - 1]; + /* can be modified without holding the LRU lock */ + atomic_long_t evicted[NR_HIST_GENS][ANON_AND_FILE][MAX_NR_TIERS]; + atomic_long_t refaulted[NR_HIST_GENS][ANON_AND_FILE][MAX_NR_TIERS]; }; void lru_gen_init_lruvec(struct lruvec *lruvec); diff --git a/kernel/bounds.c b/kernel/bounds.c index e08fb89f87f4..10dd9e6b03e5 100644 --- a/kernel/bounds.c +++ b/kernel/bounds.c @@ -24,7 +24,7 @@ int main(void) DEFINE(SPINLOCK_SIZE, sizeof(spinlock_t)); #ifdef CONFIG_LRU_GEN DEFINE(LRU_GEN_WIDTH, order_base_2(MAX_NR_GENS + 1)); - DEFINE(LRU_REFS_WIDTH, 0); + DEFINE(LRU_REFS_WIDTH, MAX_NR_TIERS - 2); #else DEFINE(LRU_GEN_WIDTH, 0); DEFINE(LRU_REFS_WIDTH, 0); diff --git a/mm/Kconfig b/mm/Kconfig index 4595fc654181..c40777d098a8 100644 --- a/mm/Kconfig +++ b/mm/Kconfig @@ -909,6 +909,7 @@ config ANON_VMA_NAME area from being merged with adjacent virtual memory areas due to the difference in their name. +# multi-gen LRU { config LRU_GEN bool "Multi-Gen LRU" depends on MMU @@ -917,6 +918,16 @@ config LRU_GEN help A high performance LRU implementation to overcommit memory. +config LRU_GEN_STATS + bool "Full stats for debugging" + depends on LRU_GEN + help + Do not enable this option unless you plan to look at historical stats + from evicted generations for debugging purpose. + + This option has a per-memcg and per-node memory overhead. +# } + source "mm/damon/Kconfig" endmenu diff --git a/mm/swap.c b/mm/swap.c index a6870ba0bd83..6a5203f18b0a 100644 --- a/mm/swap.c +++ b/mm/swap.c @@ -405,6 +405,43 @@ static void __lru_cache_activate_folio(struct folio *folio) local_unlock(&lru_pvecs.lock); } +#ifdef CONFIG_LRU_GEN +static void folio_inc_refs(struct folio *folio) +{ + unsigned long refs; + unsigned long old_flags, new_flags; + + if (folio_test_unevictable(folio)) + return; + + /* see the comment on MAX_NR_TIERS */ + do { + new_flags = old_flags = READ_ONCE(folio->flags); + + if (!(new_flags & BIT(PG_referenced))) { + new_flags |= BIT(PG_referenced); + continue; + } + + if (!(new_flags & BIT(PG_workingset))) { + new_flags |= BIT(PG_workingset); + continue; + } + + refs = new_flags & LRU_REFS_MASK; + refs = min(refs + BIT(LRU_REFS_PGOFF), LRU_REFS_MASK); + + new_flags &= ~LRU_REFS_MASK; + new_flags |= refs; + } while (new_flags != old_flags && + cmpxchg(&folio->flags, old_flags, new_flags) != old_flags); +} +#else +static void folio_inc_refs(struct folio *folio) +{ +} +#endif /* CONFIG_LRU_GEN */ + /* * Mark a page as having seen activity. * @@ -417,6 +454,11 @@ static void __lru_cache_activate_folio(struct folio *folio) */ void folio_mark_accessed(struct folio *folio) { + if (lru_gen_enabled()) { + folio_inc_refs(folio); + return; + } + if (!folio_test_referenced(folio)) { folio_set_referenced(folio); } else if (folio_test_unevictable(folio)) { diff --git a/mm/vmscan.c b/mm/vmscan.c index 37dd5d1c3d07..bb3d705c5282 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -1275,9 +1275,11 @@ static int __remove_mapping(struct address_space *mapping, struct folio *folio, if (folio_test_swapcache(folio)) { swp_entry_t swap = folio_swap_entry(folio); - mem_cgroup_swapout(folio, swap); + + /* get a shadow entry before mem_cgroup_swapout() clears folio_memcg() */ if (reclaimed && !mapping_exiting(mapping)) shadow = workingset_eviction(folio, target_memcg); + mem_cgroup_swapout(folio, swap); __delete_from_swap_cache(&folio->page, swap, shadow); xa_unlock_irq(&mapping->i_pages); put_swap_page(&folio->page, swap); @@ -2649,6 +2651,9 @@ static void prepare_scan_count(pg_data_t *pgdat, struct scan_control *sc) unsigned long file; struct lruvec *target_lruvec; + if (lru_gen_enabled()) + return; + target_lruvec = mem_cgroup_lruvec(sc->target_mem_cgroup, pgdat); /* @@ -2974,11 +2979,38 @@ static bool can_age_anon_pages(struct pglist_data *pgdat, * shorthand helpers ******************************************************************************/ +#define DEFINE_MAX_SEQ(lruvec) \ + unsigned long max_seq = READ_ONCE((lruvec)->lrugen.max_seq) + +#define DEFINE_MIN_SEQ(lruvec) \ + unsigned long min_seq[ANON_AND_FILE] = { \ + READ_ONCE((lruvec)->lrugen.min_seq[LRU_GEN_ANON]), \ + READ_ONCE((lruvec)->lrugen.min_seq[LRU_GEN_FILE]), \ + } + #define for_each_gen_type_zone(gen, type, zone) \ for ((gen) = 0; (gen) < MAX_NR_GENS; (gen)++) \ for ((type) = 0; (type) < ANON_AND_FILE; (type)++) \ for ((zone) = 0; (zone) < MAX_NR_ZONES; (zone)++) +static int folio_lru_gen(struct folio *folio) +{ + unsigned long flags = READ_ONCE(folio->flags); + + return ((flags & LRU_GEN_MASK) >> LRU_GEN_PGOFF) - 1; +} + +static int folio_lru_tier(struct folio *folio) +{ + int refs; + unsigned long flags = READ_ONCE(folio->flags); + + refs = (flags & LRU_REFS_FLAGS) == LRU_REFS_FLAGS ? + ((flags & LRU_REFS_MASK) >> LRU_REFS_PGOFF) + 1 : 0; + + return lru_tier_from_refs(refs); +} + static struct lruvec __maybe_unused *get_lruvec(struct mem_cgroup *memcg, int nid) { struct pglist_data *pgdat = NODE_DATA(nid); @@ -2999,6 +3031,754 @@ static struct lruvec __maybe_unused *get_lruvec(struct mem_cgroup *memcg, int ni return pgdat ? &pgdat->__lruvec : NULL; } +static int get_swappiness(struct lruvec *lruvec, struct scan_control *sc) +{ + struct mem_cgroup *memcg = lruvec_memcg(lruvec); + struct pglist_data *pgdat = lruvec_pgdat(lruvec); + + if (!can_demote(pgdat->node_id, sc) && + mem_cgroup_get_nr_swap_pages(memcg) < MIN_LRU_BATCH) + return 0; + + return mem_cgroup_swappiness(memcg); +} + +static int get_nr_gens(struct lruvec *lruvec, int type) +{ + return lruvec->lrugen.max_seq - lruvec->lrugen.min_seq[type] + 1; +} + +static bool __maybe_unused seq_is_valid(struct lruvec *lruvec) +{ + /* see the comment on lru_gen_struct */ + return get_nr_gens(lruvec, LRU_GEN_FILE) >= MIN_NR_GENS && + get_nr_gens(lruvec, LRU_GEN_FILE) <= get_nr_gens(lruvec, LRU_GEN_ANON) && + get_nr_gens(lruvec, LRU_GEN_ANON) <= MAX_NR_GENS; +} + +/****************************************************************************** + * refault feedback loop + ******************************************************************************/ + +/* + * A feedback loop based on Proportional-Integral-Derivative (PID) controller. + * + * The P term is refaulted/(evicted+protected) from a tier in the generation + * currently being evicted; the I term is the exponential moving average of the + * P term over the generations previously evicted, using the smoothing factor + * 1/2; the D term isn't supported. + * + * The setpoint (SP) is always the first tier of one type; the process variable + * (PV) is either any tier of the other type or any other tier of the same + * type. + * + * The error is the difference between the SP and the PV; the correction is + * turn off protection when SP>PV or turn on protection when SP<PV. + * + * For future optimizations: + * 1. The D term may discount the other two terms over time so that long-lived + * generations can resist stale information. + */ +struct ctrl_pos { + unsigned long refaulted; + unsigned long total; + int gain; +}; + +static void read_ctrl_pos(struct lruvec *lruvec, int type, int tier, int gain, + struct ctrl_pos *pos) +{ + struct lru_gen_struct *lrugen = &lruvec->lrugen; + int hist = lru_hist_from_seq(lrugen->min_seq[type]); + + pos->refaulted = lrugen->avg_refaulted[type][tier] + + atomic_long_read(&lrugen->refaulted[hist][type][tier]); + pos->total = lrugen->avg_total[type][tier] + + atomic_long_read(&lrugen->evicted[hist][type][tier]); + if (tier) + pos->total += lrugen->protected[hist][type][tier - 1]; + pos->gain = gain; +} + +static void reset_ctrl_pos(struct lruvec *lruvec, int type, bool carryover) +{ + int hist, tier; + struct lru_gen_struct *lrugen = &lruvec->lrugen; + bool clear = carryover ? NR_HIST_GENS == 1 : NR_HIST_GENS > 1; + unsigned long seq = carryover ? lrugen->min_seq[type] : lrugen->max_seq + 1; + + lockdep_assert_held(&lruvec->lru_lock); + + if (!carryover && !clear) + return; + + hist = lru_hist_from_seq(seq); + + for (tier = 0; tier < MAX_NR_TIERS; tier++) { + if (carryover) { + unsigned long sum; + + sum = lrugen->avg_refaulted[type][tier] + + atomic_long_read(&lrugen->refaulted[hist][type][tier]); + WRITE_ONCE(lrugen->avg_refaulted[type][tier], sum / 2); + + sum = lrugen->avg_total[type][tier] + + atomic_long_read(&lrugen->evicted[hist][type][tier]); + if (tier) + sum += lrugen->protected[hist][type][tier - 1]; + WRITE_ONCE(lrugen->avg_total[type][tier], sum / 2); + } + + if (clear) { + atomic_long_set(&lrugen->refaulted[hist][type][tier], 0); + atomic_long_set(&lrugen->evicted[hist][type][tier], 0); + if (tier) + WRITE_ONCE(lrugen->protected[hist][type][tier - 1], 0); + } + } +} + +static bool positive_ctrl_err(struct ctrl_pos *sp, struct ctrl_pos *pv) +{ + /* + * Return true if the PV has a limited number of refaults or a lower + * refaulted/total than the SP. + */ + return pv->refaulted < MIN_LRU_BATCH || + pv->refaulted * (sp->total + MIN_LRU_BATCH) * sp->gain <= + (sp->refaulted + 1) * pv->total * pv->gain; +} + +/****************************************************************************** + * the aging + ******************************************************************************/ + +static int folio_inc_gen(struct lruvec *lruvec, struct folio *folio, bool reclaiming) +{ + unsigned long old_flags, new_flags; + int type = folio_is_file_lru(folio); + struct lru_gen_struct *lrugen = &lruvec->lrugen; + int new_gen, old_gen = lru_gen_from_seq(lrugen->min_seq[type]); + + do { + new_flags = old_flags = READ_ONCE(folio->flags); + VM_BUG_ON_FOLIO(!(new_flags & LRU_GEN_MASK), folio); + + new_gen = (old_gen + 1) % MAX_NR_GENS; + + new_flags &= ~LRU_GEN_MASK; + new_flags |= (new_gen + 1UL) << LRU_GEN_PGOFF; + new_flags &= ~(LRU_REFS_MASK | LRU_REFS_FLAGS); + /* for folio_end_writeback() */ + if (reclaiming) + new_flags |= BIT(PG_reclaim); + } while (cmpxchg(&folio->flags, old_flags, new_flags) != old_flags); + + lru_gen_update_size(lruvec, folio, old_gen, new_gen); + + return new_gen; +} + +static void inc_min_seq(struct lruvec *lruvec) +{ + int type; + struct lru_gen_struct *lrugen = &lruvec->lrugen; + + VM_BUG_ON(!seq_is_valid(lruvec)); + + for (type = 0; type < ANON_AND_FILE; type++) { + if (get_nr_gens(lruvec, type) != MAX_NR_GENS) + continue; + + reset_ctrl_pos(lruvec, type, true); + WRITE_ONCE(lrugen->min_seq[type], lrugen->min_seq[type] + 1); + } +} + +static bool try_to_inc_min_seq(struct lruvec *lruvec, bool can_swap) +{ + int gen, type, zone; + bool success = false; + struct lru_gen_struct *lrugen = &lruvec->lrugen; + DEFINE_MIN_SEQ(lruvec); + + VM_BUG_ON(!seq_is_valid(lruvec)); + + for (type = !can_swap; type < ANON_AND_FILE; type++) { + while (min_seq[type] + MIN_NR_GENS <= lrugen->max_seq) { + gen = lru_gen_from_seq(min_seq[type]); + + for (zone = 0; zone < MAX_NR_ZONES; zone++) { + if (!list_empty(&lrugen->lists[gen][type][zone])) + goto next; + } + + min_seq[type]++; + } +next: + ; + } + + /* see the comment on lru_gen_struct */ + if (can_swap) { + min_seq[LRU_GEN_ANON] = min(min_seq[LRU_GEN_ANON], min_seq[LRU_GEN_FILE]); + min_seq[LRU_GEN_FILE] = max(min_seq[LRU_GEN_ANON], lrugen->min_seq[LRU_GEN_FILE]); + } + + for (type = !can_swap; type < ANON_AND_FILE; type++) { + if (min_seq[type] == lrugen->min_seq[type]) + continue; + + reset_ctrl_pos(lruvec, type, true); + WRITE_ONCE(lrugen->min_seq[type], min_seq[type]); + success = true; + } + + return success; +} + +static void inc_max_seq(struct lruvec *lruvec, unsigned long max_seq) +{ + int prev, next; + int type, zone; + struct lru_gen_struct *lrugen = &lruvec->lrugen; + + spin_lock_irq(&lruvec->lru_lock); + + VM_BUG_ON(!seq_is_valid(lruvec)); + + if (max_seq != lrugen->max_seq) + goto unlock; + + inc_min_seq(lruvec); + + /* + * Update the active/inactive LRU sizes for compatibility. Both sides of + * the current max_seq need to be covered, since max_seq+1 can overlap + * with min_seq[LRU_GEN_ANON] if swapping is constrained. And if they do + * overlap, cold/hot inversion happens. This can be solved by moving + * pages from min_seq to min_seq+1 but is omitted for simplicity. + */ + prev = lru_gen_from_seq(lrugen->max_seq - 1); + next = lru_gen_from_seq(lrugen->max_seq + 1); + + for (type = 0; type < ANON_AND_FILE; type++) { + for (zone = 0; zone < MAX_NR_ZONES; zone++) { + enum lru_list lru = type * LRU_INACTIVE_FILE; + long delta = lrugen->nr_pages[prev][type][zone] - + lrugen->nr_pages[next][type][zone]; + + if (!delta) + continue; + + __update_lru_size(lruvec, lru, zone, delta); + __update_lru_size(lruvec, lru + LRU_ACTIVE, zone, -delta); + } + } + + for (type = 0; type < ANON_AND_FILE; type++) + reset_ctrl_pos(lruvec, type, false); + + /* make sure preceding modifications appear */ + smp_store_release(&lrugen->max_seq, lrugen->max_seq + 1); +unlock: + spin_unlock_irq(&lruvec->lru_lock); +} + +static long get_nr_evictable(struct lruvec *lruvec, unsigned long max_seq, + unsigned long *min_seq, bool can_swap, bool *need_aging) +{ + int gen, type, zone; + long old = 0; + long young = 0; + long total = 0; + struct lru_gen_struct *lrugen = &lruvec->lrugen; + + for (type = !can_swap; type < ANON_AND_FILE; type++) { + unsigned long seq; + + for (seq = min_seq[type]; seq <= max_seq; seq++) { + long size = 0; + + gen = lru_gen_from_seq(seq); + + for (zone = 0; zone < MAX_NR_ZONES; zone++) + size += READ_ONCE(lrugen->nr_pages[gen][type][zone]); + + total += size; + if (seq == max_seq) + young += size; + if (seq + MIN_NR_GENS == max_seq) + old += size; + } + } + + /* + * The aging and the eviction is a typical producer-consumer model. The + * aging tries to be lazy to reduce the unnecessary overhead. On the + * other hand, the eviction stalls when the number of generations + * reaches MIN_NR_GENS. So ideally, there should be MIN_NR_GENS+1 + * generations, hence the first two if's. + * + * In addition, it's ideal to spread pages out evenly, meaning + * 1/(MIN_NR_GENS+1) of the total number of pages for each generation. A + * reasonable range for this average portion would [1/MIN_NR_GENS, + * 1/(MIN_NR_GENS+2)]. From the consumer's POV, the eviction only cares + * about the lower bound of cold pages, i.e., 1/(MIN_NR_GENS+2), whereas + * from the producer's POV, the aging only cares about the upper bound + * of hot pages, i.e., 1/MIN_NR_GENS. + */ + if (min_seq[LRU_GEN_FILE] + MIN_NR_GENS > max_seq) + *need_aging = true; + else if (min_seq[LRU_GEN_FILE] + MIN_NR_GENS < max_seq) + *need_aging = false; + else if (young * MIN_NR_GENS > total) + *need_aging = true; + else if (old * (MIN_NR_GENS + 2) < total) + *need_aging = true; + else + *need_aging = false; + + return total > 0 ? total : 0; +} + +static void age_lruvec(struct lruvec *lruvec, struct scan_control *sc) +{ + bool need_aging; + long nr_to_scan; + int swappiness = get_swappiness(lruvec, sc); + struct mem_cgroup *memcg = lruvec_memcg(lruvec); + DEFINE_MAX_SEQ(lruvec); + DEFINE_MIN_SEQ(lruvec); + + mem_cgroup_calculate_protection(NULL, memcg); + + if (mem_cgroup_below_min(memcg)) + return; + + nr_to_scan = get_nr_evictable(lruvec, max_seq, min_seq, swappiness, &need_aging); + if (!nr_to_scan) + return; + + nr_to_scan >>= sc->priority; + + if (!mem_cgroup_online(memcg)) + nr_to_scan++; + + if (nr_to_scan && need_aging && (!mem_cgroup_below_low(memcg) || sc->memcg_low_reclaim)) + inc_max_seq(lruvec, max_seq); +} + +static void lru_gen_age_node(struct pglist_data *pgdat, struct scan_control *sc) +{ + struct mem_cgroup *memcg; + + VM_BUG_ON(!current_is_kswapd()); + + memcg = mem_cgroup_iter(NULL, NULL, NULL); + do { + struct lruvec *lruvec = mem_cgroup_lruvec(memcg, pgdat); + + age_lruvec(lruvec, sc); + + cond_resched(); + } while ((memcg = mem_cgroup_iter(NULL, memcg, NULL))); +} + +/****************************************************************************** + * the eviction + ******************************************************************************/ + +static bool sort_folio(struct lruvec *lruvec, struct folio *folio, int tier_idx) +{ + bool success; + int gen = folio_lru_gen(folio); + int type = folio_is_file_lru(folio); + int zone = folio_zonenum(folio); + int tier = folio_lru_tier(folio); + int delta = folio_nr_pages(folio); + struct lru_gen_struct *lrugen = &lruvec->lrugen; + + VM_BUG_ON_FOLIO(gen >= MAX_NR_GENS, folio); + + if (!folio_evictable(folio)) { + success = lru_gen_del_folio(lruvec, folio, true); + VM_BUG_ON_FOLIO(!success, folio); + folio_set_unevictable(folio); + lruvec_add_folio(lruvec, folio); + __count_vm_events(UNEVICTABLE_PGCULLED, delta); + return true; + } + + if (type == LRU_GEN_FILE && folio_test_anon(folio) && folio_test_dirty(folio)) { + success = lru_gen_del_folio(lruvec, folio, true); + VM_BUG_ON_FOLIO(!success, folio); + folio_set_swapbacked(folio); + lruvec_add_folio_tail(lruvec, folio); + return true; + } + + if (tier > tier_idx) { + int hist = lru_hist_from_seq(lrugen->min_seq[type]); + + gen = folio_inc_gen(lruvec, folio, false); + list_move_tail(&folio->lru, &lrugen->lists[gen][type][zone]); + + WRITE_ONCE(lrugen->protected[hist][type][tier - 1], + lrugen->protected[hist][type][tier - 1] + delta); + __mod_lruvec_state(lruvec, WORKINGSET_ACTIVATE_BASE + type, delta); + return true; + } + + if (folio_test_locked(folio) || folio_test_writeback(folio) || + (type == LRU_GEN_FILE && folio_test_dirty(folio))) { + gen = folio_inc_gen(lruvec, folio, true); + list_move(&folio->lru, &lrugen->lists[gen][type][zone]); + return true; + } + + return false; +} + +static bool isolate_folio(struct lruvec *lruvec, struct folio *folio, struct scan_control *sc) +{ + bool success; + + if (!sc->may_unmap && folio_mapped(folio)) + return false; + + if (!(sc->may_writepage && (sc->gfp_mask & __GFP_IO)) && + (folio_test_dirty(folio) || + (folio_test_anon(folio) && !folio_test_swapcache(folio)))) + return false; + + if (!folio_try_get(folio)) + return false; + + if (!folio_test_clear_lru(folio)) { + folio_put(folio); + return false; + } + + success = lru_gen_del_folio(lruvec, folio, true); + VM_BUG_ON_FOLIO(!success, folio); + + return true; +} + +static int scan_folios(struct lruvec *lruvec, struct scan_control *sc, + int type, int tier, struct list_head *list) +{ + int gen, zone; + enum vm_event_item item; + int sorted = 0; + int scanned = 0; + int isolated = 0; + int remaining = MAX_LRU_BATCH; + struct lru_gen_struct *lrugen = &lruvec->lrugen; + struct mem_cgroup *memcg = lruvec_memcg(lruvec); + + VM_BUG_ON(!list_empty(list)); + + if (get_nr_gens(lruvec, type) == MIN_NR_GENS) + return 0; + + gen = lru_gen_from_seq(lrugen->min_seq[type]); + + for (zone = sc->reclaim_idx; zone >= 0; zone--) { + LIST_HEAD(moved); + int skipped = 0; + struct list_head *head = &lrugen->lists[gen][type][zone]; + + while (!list_empty(head)) { + struct folio *folio = lru_to_folio(head); + int delta = folio_nr_pages(folio); + + VM_BUG_ON_FOLIO(folio_test_unevictable(folio), folio); + VM_BUG_ON_FOLIO(folio_test_active(folio), folio); + VM_BUG_ON_FOLIO(folio_is_file_lru(folio) != type, folio); + VM_BUG_ON_FOLIO(folio_zonenum(folio) != zone, folio); + + scanned += delta; + + if (sort_folio(lruvec, folio, tier)) + sorted += delta; + else if (isolate_folio(lruvec, folio, sc)) { + list_add(&folio->lru, list); + isolated += delta; + } else { + list_move(&folio->lru, &moved); + skipped += delta; + } + + if (!--remaining || max(isolated, skipped) >= MIN_LRU_BATCH) + break; + } + + if (skipped) { + list_splice(&moved, head); + __count_zid_vm_events(PGSCAN_SKIP, zone, skipped); + } + + if (!remaining || isolated >= MIN_LRU_BATCH) + break; + } + + item = current_is_kswapd() ? PGSCAN_KSWAPD : PGSCAN_DIRECT; + if (!cgroup_reclaim(sc)) { + __count_vm_events(item, isolated); + __count_vm_events(PGREFILL, sorted); + } + __count_memcg_events(memcg, item, isolated); + __count_memcg_events(memcg, PGREFILL, sorted); + __count_vm_events(PGSCAN_ANON + type, isolated); + + /* + * There might not be eligible pages due to reclaim_idx, may_unmap and + * may_writepage. Check the remaining to prevent livelock if there is no + * progress. + */ + return isolated || !remaining ? scanned : 0; +} + +static int get_tier_idx(struct lruvec *lruvec, int type) +{ + int tier; + struct ctrl_pos sp, pv; + + /* + * To leave a margin for fluctuations, use a larger gain factor (1:2). + * This value is chosen because any other tier would have at least twice + * as many refaults as the first tier. + */ + read_ctrl_pos(lruvec, type, 0, 1, &sp); + for (tier = 1; tier < MAX_NR_TIERS; tier++) { + read_ctrl_pos(lruvec, type, tier, 2, &pv); + if (!positive_ctrl_err(&sp, &pv)) + break; + } + + return tier - 1; +} + +static int get_type_to_scan(struct lruvec *lruvec, int swappiness, int *tier_idx) +{ + int type, tier; + struct ctrl_pos sp, pv; + int gain[ANON_AND_FILE] = { swappiness, 200 - swappiness }; + + /* + * Compare the first tier of anon with that of file to determine which + * type to scan. Also need to compare other tiers of the selected type + * with the first tier of the other type to determine the last tier (of + * the selected type) to evict. + */ + read_ctrl_pos(lruvec, LRU_GEN_ANON, 0, gain[LRU_GEN_ANON], &sp); + read_ctrl_pos(lruvec, LRU_GEN_FILE, 0, gain[LRU_GEN_FILE], &pv); + type = positive_ctrl_err(&sp, &pv); + + read_ctrl_pos(lruvec, !type, 0, gain[!type], &sp); + for (tier = 1; tier < MAX_NR_TIERS; tier++) { + read_ctrl_pos(lruvec, type, tier, gain[type], &pv); + if (!positive_ctrl_err(&sp, &pv)) + break; + } + + *tier_idx = tier - 1; + + return type; +} + +static int isolate_folios(struct lruvec *lruvec, struct scan_control *sc, int swappiness, + int *type_scanned, struct list_head *list) +{ + int i; + int type; + int scanned; + int tier = -1; + DEFINE_MIN_SEQ(lruvec); + + VM_BUG_ON(!seq_is_valid(lruvec)); + + /* + * Try to make the obvious choice first. When anon and file are both + * available from the same generation, interpret swappiness 1 as file + * first and 200 as anon first. + */ + if (!swappiness) + type = LRU_GEN_FILE; + else if (min_seq[LRU_GEN_ANON] < min_seq[LRU_GEN_FILE]) + type = LRU_GEN_ANON; + else if (swappiness == 1) + type = LRU_GEN_FILE; + else if (swappiness == 200) + type = LRU_GEN_ANON; + else + type = get_type_to_scan(lruvec, swappiness, &tier); + + for (i = !swappiness; i < ANON_AND_FILE; i++) { + if (tier < 0) + tier = get_tier_idx(lruvec, type); + + scanned = scan_folios(lruvec, sc, type, tier, list); + if (scanned) + break; + + type = !type; + tier = -1; + } + + *type_scanned = type; + + return scanned; +} + +static int evict_folios(struct lruvec *lruvec, struct scan_control *sc, int swappiness) +{ + int type; + int scanned; + int reclaimed; + LIST_HEAD(list); + struct folio *folio; + enum vm_event_item item; + struct reclaim_stat stat; + struct mem_cgroup *memcg = lruvec_memcg(lruvec); + struct pglist_data *pgdat = lruvec_pgdat(lruvec); + + spin_lock_irq(&lruvec->lru_lock); + + scanned = isolate_folios(lruvec, sc, swappiness, &type, &list); + + if (try_to_inc_min_seq(lruvec, swappiness)) + scanned++; + + if (get_nr_gens(lruvec, LRU_GEN_FILE) == MIN_NR_GENS) + scanned = 0; + + spin_unlock_irq(&lruvec->lru_lock); + + if (list_empty(&list)) + return scanned; + + reclaimed = shrink_page_list(&list, pgdat, sc, &stat, false); + + /* + * To avoid livelock, don't add rejected pages back to the same lists + * they were isolated from. See lru_gen_add_folio(). + */ + list_for_each_entry(folio, &list, lru) { + folio_clear_referenced(folio); + folio_clear_workingset(folio); + + if (folio_test_reclaim(folio) && + (folio_test_dirty(folio) || folio_test_writeback(folio))) + folio_clear_active(folio); + else + folio_set_active(folio); + } + + spin_lock_irq(&lruvec->lru_lock); + + move_pages_to_lru(lruvec, &list); + + item = current_is_kswapd() ? PGSTEAL_KSWAPD : PGSTEAL_DIRECT; + if (!cgroup_reclaim(sc)) + __count_vm_events(item, reclaimed); + __count_memcg_events(memcg, item, reclaimed); + __count_vm_events(PGSTEAL_ANON + type, reclaimed); + + spin_unlock_irq(&lruvec->lru_lock); + + mem_cgroup_uncharge_list(&list); + free_unref_page_list(&list); + + sc->nr_reclaimed += reclaimed; + + return scanned; +} + +static long get_nr_to_scan(struct lruvec *lruvec, struct scan_control *sc, bool can_swap) +{ + bool need_aging; + long nr_to_scan; + struct mem_cgroup *memcg = lruvec_memcg(lruvec); + DEFINE_MAX_SEQ(lruvec); + DEFINE_MIN_SEQ(lruvec); + + if (mem_cgroup_below_min(memcg) || + (mem_cgroup_below_low(memcg) && !sc->memcg_low_reclaim)) + return 0; + + nr_to_scan = get_nr_evictable(lruvec, max_seq, min_seq, can_swap, &need_aging); + if (!nr_to_scan) + return 0; + + /* reset the priority if the target has been met */ + nr_to_scan >>= sc->nr_reclaimed < sc->nr_to_reclaim ? sc->priority : DEF_PRIORITY; + + if (!mem_cgroup_online(memcg)) + nr_to_scan++; + + if (!nr_to_scan) + return 0; + + if (!need_aging) + return nr_to_scan; + + /* leave the work to lru_gen_age_node() */ + if (current_is_kswapd()) + return 0; + + /* try other memcgs before going to the aging path */ + if (!cgroup_reclaim(sc) && !sc->force_deactivate) { + sc->skipped_deactivate = true; + return 0; + } + + inc_max_seq(lruvec, max_seq); + + return nr_to_scan; +} + +static void lru_gen_shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc) +{ + struct blk_plug plug; + long scanned = 0; + + lru_add_drain(); + + blk_start_plug(&plug); + + while (true) { + int delta; + int swappiness; + long nr_to_scan; + + if (sc->may_swap) + swappiness = get_swappiness(lruvec, sc); + else if (!cgroup_reclaim(sc) && get_swappiness(lruvec, sc)) + swappiness = 1; + else + swappiness = 0; + + nr_to_scan = get_nr_to_scan(lruvec, sc, swappiness); + if (!nr_to_scan) + break; + + delta = evict_folios(lruvec, sc, swappiness); + if (!delta) + break; + + scanned += delta; + if (scanned >= nr_to_scan) + break; + + cond_resched(); + } + + blk_finish_plug(&plug); +} + /****************************************************************************** * initialization ******************************************************************************/ @@ -3041,6 +3821,16 @@ static int __init init_lru_gen(void) }; late_initcall(init_lru_gen); +#else + +static void lru_gen_age_node(struct pglist_data *pgdat, struct scan_control *sc) +{ +} + +static void lru_gen_shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc) +{ +} + #endif /* CONFIG_LRU_GEN */ static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc) @@ -3054,6 +3844,11 @@ static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc) struct blk_plug plug; bool scan_adjusted; + if (lru_gen_enabled()) { + lru_gen_shrink_lruvec(lruvec, sc); + return; + } + get_scan_count(lruvec, sc, nr); /* Record the original scan target for proportional adjustments later */ @@ -3558,6 +4353,9 @@ static void snapshot_refaults(struct mem_cgroup *target_memcg, pg_data_t *pgdat) struct lruvec *target_lruvec; unsigned long refaults; + if (lru_gen_enabled()) + return; + target_lruvec = mem_cgroup_lruvec(target_memcg, pgdat); refaults = lruvec_page_state(target_lruvec, WORKINGSET_ACTIVATE_ANON); target_lruvec->refaults[0] = refaults; @@ -3928,6 +4726,11 @@ static void age_active_anon(struct pglist_data *pgdat, struct mem_cgroup *memcg; struct lruvec *lruvec; + if (lru_gen_enabled()) { + lru_gen_age_node(pgdat, sc); + return; + } + if (!can_age_anon_pages(pgdat, sc)) return; diff --git a/mm/workingset.c b/mm/workingset.c index 8a3828acc0bf..89b46af74eef 100644 --- a/mm/workingset.c +++ b/mm/workingset.c @@ -187,7 +187,6 @@ static unsigned int bucket_order __read_mostly; static void *pack_shadow(int memcgid, pg_data_t *pgdat, unsigned long eviction, bool workingset) { - eviction >>= bucket_order; eviction &= EVICTION_MASK; eviction = (eviction << MEM_CGROUP_ID_SHIFT) | memcgid; eviction = (eviction << NODES_SHIFT) | pgdat->node_id; @@ -212,10 +211,116 @@ static void unpack_shadow(void *shadow, int *memcgidp, pg_data_t **pgdat, *memcgidp = memcgid; *pgdat = NODE_DATA(nid); - *evictionp = entry << bucket_order; + *evictionp = entry; *workingsetp = workingset; } +#ifdef CONFIG_LRU_GEN + +static int folio_lru_refs(struct folio *folio) +{ + unsigned long flags = READ_ONCE(folio->flags); + + BUILD_BUG_ON(LRU_GEN_WIDTH + LRU_REFS_WIDTH > BITS_PER_LONG - EVICTION_SHIFT); + + /* see the comment on MAX_NR_TIERS */ + return flags & BIT(PG_workingset) ? (flags & LRU_REFS_MASK) >> LRU_REFS_PGOFF : 0; +} + +static void *lru_gen_eviction(struct folio *folio) +{ + int hist, tier; + unsigned long token; + unsigned long min_seq; + struct lruvec *lruvec; + struct lru_gen_struct *lrugen; + int type = folio_is_file_lru(folio); + int refs = folio_lru_refs(folio); + int delta = folio_nr_pages(folio); + bool workingset = folio_test_workingset(folio); + struct mem_cgroup *memcg = folio_memcg(folio); + struct pglist_data *pgdat = folio_pgdat(folio); + + lruvec = mem_cgroup_lruvec(memcg, pgdat); + lrugen = &lruvec->lrugen; + min_seq = READ_ONCE(lrugen->min_seq[type]); + token = (min_seq << LRU_REFS_WIDTH) | refs; + + hist = lru_hist_from_seq(min_seq); + tier = lru_tier_from_refs(refs + workingset); + atomic_long_add(delta, &lrugen->evicted[hist][type][tier]); + + return pack_shadow(mem_cgroup_id(memcg), pgdat, token, workingset); +} + +static void lru_gen_refault(struct folio *folio, void *shadow) +{ + int hist, tier, refs; + int memcg_id; + bool workingset; + unsigned long token; + unsigned long min_seq; + struct lruvec *lruvec; + struct lru_gen_struct *lrugen; + struct mem_cgroup *memcg; + struct pglist_data *pgdat; + int type = folio_is_file_lru(folio); + int delta = folio_nr_pages(folio); + + unpack_shadow(shadow, &memcg_id, &pgdat, &token, &workingset); + + refs = token & (BIT(LRU_REFS_WIDTH) - 1); + if (refs && !workingset) + return; + + if (folio_pgdat(folio) != pgdat) + return; + + rcu_read_lock(); + memcg = folio_memcg_rcu(folio); + if (mem_cgroup_id(memcg) != memcg_id) + goto unlock; + + token >>= LRU_REFS_WIDTH; + lruvec = mem_cgroup_lruvec(memcg, pgdat); + lrugen = &lruvec->lrugen; + min_seq = READ_ONCE(lrugen->min_seq[type]); + if (token != (min_seq & (EVICTION_MASK >> LRU_REFS_WIDTH))) + goto unlock; + + hist = lru_hist_from_seq(min_seq); + tier = lru_tier_from_refs(refs + workingset); + atomic_long_add(delta, &lrugen->refaulted[hist][type][tier]); + mod_lruvec_state(lruvec, WORKINGSET_REFAULT_BASE + type, delta); + + /* + * Count the following two cases as stalls: + * 1. For pages accessed through page tables, hotter pages pushed out + * hot pages which refaulted immediately. + * 2. For pages accessed through file descriptors, numbers of accesses + * might have been beyond the limit. + */ + if (lru_gen_in_fault() || refs + workingset == BIT(LRU_REFS_WIDTH)) { + folio_set_workingset(folio); + mod_lruvec_state(lruvec, WORKINGSET_RESTORE_BASE + type, delta); + } +unlock: + rcu_read_unlock(); +} + +#else + +static void *lru_gen_eviction(struct folio *folio) +{ + return NULL; +} + +static void lru_gen_refault(struct folio *folio, void *shadow) +{ +} + +#endif /* CONFIG_LRU_GEN */ + /** * workingset_age_nonresident - age non-resident entries as LRU ages * @lruvec: the lruvec that was aged @@ -264,10 +369,14 @@ void *workingset_eviction(struct folio *folio, struct mem_cgroup *target_memcg) VM_BUG_ON_FOLIO(folio_ref_count(folio), folio); VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio); + if (lru_gen_enabled()) + return lru_gen_eviction(folio); + lruvec = mem_cgroup_lruvec(target_memcg, pgdat); /* XXX: target_memcg can be NULL, go through lruvec */ memcgid = mem_cgroup_id(lruvec_memcg(lruvec)); eviction = atomic_long_read(&lruvec->nonresident_age); + eviction >>= bucket_order; workingset_age_nonresident(lruvec, folio_nr_pages(folio)); return pack_shadow(memcgid, pgdat, eviction, folio_test_workingset(folio)); @@ -298,7 +407,13 @@ void workingset_refault(struct folio *folio, void *shadow) int memcgid; long nr; + if (lru_gen_enabled()) { + lru_gen_refault(folio, shadow); + return; + } + unpack_shadow(shadow, &memcgid, &pgdat, &eviction, &workingset); + eviction <<= bucket_order; rcu_read_lock(); /*
To avoid confusion, the terms "promotion" and "demotion" will be applied to the multi-gen LRU, as a new convention; the terms "activation" and "deactivation" will be applied to the active/inactive LRU, as usual. The aging produces young generations. Given an lruvec, it increments max_seq when max_seq-min_seq+1 approaches MIN_NR_GENS. The aging promotes hot pages to the youngest generation when it finds them accessed through page tables; the demotion of cold pages happens consequently when it increments max_seq. The aging has the complexity O(nr_hot_pages), since it is only interested in hot pages. Promotion in the aging path does not require any LRU list operations, only the updates of the gen counter and lrugen->nr_pages[]; demotion, unless as the result of the increment of max_seq, requires LRU list operations, e.g., lru_deactivate_fn(). The eviction consumes old generations. Given an lruvec, it increments min_seq when the lists indexed by min_seq%MAX_NR_GENS become empty. A feedback loop modeled after the PID controller monitors refaults over anon and file types and decides which type to evict when both types are available from the same generation. Each generation is divided into multiple tiers. Tiers represent different ranges of numbers of accesses through file descriptors. A page accessed N times through file descriptors is in tier order_base_2(N). Tiers do not have dedicated lrugen->lists[], only bits in folio->flags. In contrast to moving across generations, which requires the LRU lock, moving across tiers only involves operations on folio->flags. The feedback loop also monitors refaults over all tiers and decides when to protect pages in which tiers (N>1), using the first tier (N=0,1) as a baseline. The first tier contains single-use unmapped clean pages, which are most likely the best choices. The eviction moves a page to the next generation, i.e., min_seq+1, if the feedback loop decides so. This approach has the following advantages: 1. It removes the cost of activation in the buffered access path by inferring whether pages accessed multiple times through file descriptors are statistically hot and thus worth protecting in the eviction path. 2. It takes pages accessed through page tables into account and avoids overprotecting pages accessed multiple times through file descriptors. (Pages accessed through page tables are in the first tier, since N=0.) 3. More tiers provide better protection for pages accessed more than twice through file descriptors, when under heavy buffered I/O workloads. Server benchmark results: Single workload: fio (buffered I/O): +[40, 42]% IOPS BW 5.18-rc1: 2463k 9621MiB/s patch1-6: 3484k 13.3GiB/s Single workload: memcached (anon): +[44, 46]% Ops/sec KB/sec 5.18-rc1: 771403.27 30004.17 patch1-6: 1120643.70 43588.06 Configurations: CPU: two Xeon 6154 Mem: total 256G Node 1 was only used as a ram disk to reduce the variance in the results. patch drivers/block/brd.c <<EOF 99,100c99,100 < gfp_flags = GFP_NOIO | __GFP_ZERO | __GFP_HIGHMEM; < page = alloc_page(gfp_flags); --- > gfp_flags = GFP_NOIO | __GFP_ZERO | __GFP_HIGHMEM | __GFP_THISNODE; > page = alloc_pages_node(1, gfp_flags, 0); EOF cat >>/etc/systemd/system.conf <<EOF CPUAffinity=numa NUMAPolicy=bind NUMAMask=0 EOF cat >>/etc/memcached.conf <<EOF -m 184320 -s /var/run/memcached/memcached.sock -a 0766 -t 36 -B binary EOF cat fio.sh modprobe brd rd_nr=1 rd_size=113246208 swapoff -a mkfs.ext4 /dev/ram0 mount -t ext4 /dev/ram0 /mnt mkdir /sys/fs/cgroup/user.slice/test echo 38654705664 >/sys/fs/cgroup/user.slice/test/memory.max echo $$ >/sys/fs/cgroup/user.slice/test/cgroup.procs fio -name=mglru --numjobs=72 --directory=/mnt --size=1408m \ --buffered=1 --ioengine=io_uring --iodepth=128 \ --iodepth_batch_submit=32 --iodepth_batch_complete=32 \ --rw=randread --random_distribution=random --norandommap \ --time_based --ramp_time=10m --runtime=5m --group_reporting cat memcached.sh modprobe brd rd_nr=1 rd_size=113246208 swapoff -a mkswap /dev/ram0 swapon /dev/ram0 memtier_benchmark -S /var/run/memcached/memcached.sock \ -P memcache_binary -n allkeys --key-minimum=1 \ --key-maximum=65000000 --key-pattern=P:P -c 1 -t 36 \ --ratio 1:0 --pipeline 8 -d 2000 memtier_benchmark -S /var/run/memcached/memcached.sock \ -P memcache_binary -n allkeys --key-minimum=1 \ --key-maximum=65000000 --key-pattern=R:R -c 1 -t 36 \ --ratio 0:1 --pipeline 8 --randomize --distinct-client-seed Client benchmark results: kswapd profiles: 5.18-rc1 40.53% page_vma_mapped_walk 20.37% lzo1x_1_do_compress (real work) 6.99% do_raw_spin_lock 3.93% _raw_spin_unlock_irq 2.08% vma_interval_tree_subtree_search 2.06% vma_interval_tree_iter_next 1.95% folio_referenced_one 1.93% anon_vma_interval_tree_iter_first 1.51% ptep_clear_flush 1.35% __anon_vma_interval_tree_subtree_search patch1-6 35.99% lzo1x_1_do_compress (real work) 19.40% page_vma_mapped_walk 6.31% _raw_spin_unlock_irq 3.95% do_raw_spin_lock 2.39% anon_vma_interval_tree_iter_first 2.25% ptep_clear_flush 1.92% __anon_vma_interval_tree_subtree_search 1.70% folio_referenced_one 1.68% __zram_bvec_write 1.43% anon_vma_interval_tree_iter_next Configurations: CPU: single Snapdragon 7c Mem: total 4G Chrome OS MemoryPressure [1] [1] https://chromium.googlesource.com/chromiumos/platform/tast-tests/ Signed-off-by: Yu Zhao <yuzhao@google.com> Acked-by: Brian Geffon <bgeffon@google.com> Acked-by: Jan Alexander Steffens (heftig) <heftig@archlinux.org> Acked-by: Oleksandr Natalenko <oleksandr@natalenko.name> Acked-by: Steven Barrett <steven@liquorix.net> Acked-by: Suleiman Souhlal <suleiman@google.com> Tested-by: Daniel Byrne <djbyrne@mtu.edu> Tested-by: Donald Carr <d@chaos-reins.com> Tested-by: Holger Hoffstätte <holger@applied-asynchrony.com> Tested-by: Konstantin Kharlamov <Hi-Angel@yandex.ru> Tested-by: Shuang Zhai <szhai2@cs.rochester.edu> Tested-by: Sofia Trinh <sofia.trinh@edi.works> Tested-by: Vaibhav Jain <vaibhav@linux.ibm.com> --- include/linux/mm_inline.h | 24 ++ include/linux/mmzone.h | 41 ++ kernel/bounds.c | 2 +- mm/Kconfig | 11 + mm/swap.c | 42 ++ mm/vmscan.c | 805 +++++++++++++++++++++++++++++++++++++- mm/workingset.c | 119 +++++- 7 files changed, 1040 insertions(+), 4 deletions(-)