| Message ID | 20240311161214.1145168-1-hannes@cmpxchg.org (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [1/2] mm: zswap: optimize zswap pool size tracking | expand |
On Mon, Mar 11, 2024 at 12:12:13PM -0400, Johannes Weiner wrote: > Profiling the munmap() of a zswapped memory region shows 50%(!) of the > total cycles currently going into updating the zswap_pool_total_size. Yikes. I have always hated that size update scheme FWIW. I have also wondered whether it makes sense to just maintain the number of pages in zswap as an atomic, like zswap_stored_pages. I guess your proposed scheme is even cheaper for the load/invalidate paths because we do nothing at all. It could be an option if the aggregation in other paths ever becomes a problem, but we would need to make sure it doesn't regress the load/invalidate paths. Just sharing some thoughts. > > There are three consumers of this counter: > - store, to enforce the globally configured pool limit > - meminfo & debugfs, to report the size to the user > - shrink, to determine the batch size for each cycle > > Instead of aggregating everytime an entry enters or exits the zswap > pool, aggregate the value from the zpools on-demand: > > - Stores aggregate the counter anyway upon success. Aggregating to > check the limit instead is the same amount of work. > > - Meminfo & debugfs might benefit somewhat from a pre-aggregated > counter, but aren't exactly hotpaths. > > - Shrinking can aggregate once for every cycle instead of doing it for > every freed entry. As the shrinker might work on tens or hundreds of > objects per scan cycle, this is a large reduction in aggregations. > > The paths that benefit dramatically are swapin, swapoff, and > unmaps. There could be millions of pages being processed until > somebody asks for the pool size again. This eliminates the pool size > updates from those paths entirely. This looks like a big win, thanks! I wonder if you have any numbers of perf profiles to share. That would be nice to have, but I think the benefit is clear regardless. I also like the implicit cleanup when we switch to maintaining the number of pages rather than bytes. The code looks much better with all the shifts and divisions gone :) I have a couple of comments below. With them addressed, feel free to add: Acked-by: Yosry Ahmed <yosryahmed@google.com> [..] > @@ -1385,6 +1365,10 @@ static void shrink_worker(struct work_struct *w) > { > struct mem_cgroup *memcg; > int ret, failures = 0; > + unsigned long thr; > + > + /* Reclaim down to the accept threshold */ > + thr = zswap_max_pages() * zswap_accept_thr_percent / 100; This calculation is repeated twice, so I'd rather keep a helper for it as an alternative to zswap_can_accept(). Perhaps zswap_threshold_page() or zswap_acceptance_pages()? > > /* global reclaim will select cgroup in a round-robin fashion. */ > do { > @@ -1432,10 +1416,9 @@ static void shrink_worker(struct work_struct *w) > break; > if (ret && ++failures == MAX_RECLAIM_RETRIES) > break; > - > resched: > cond_resched(); > - } while (!zswap_can_accept()); > + } while (zswap_total_pages() > thr); > } [..] > @@ -1711,6 +1700,13 @@ void zswap_swapoff(int type) > > static struct dentry *zswap_debugfs_root; > > +static int debugfs_get_total_size(void *data, u64 *val) > +{ > + *val = zswap_total_pages() * PAGE_SIZE; > + return 0; > +} > +DEFINE_DEBUGFS_ATTRIBUTE(total_size_fops, debugfs_get_total_size, NULL, "%llu"); I think we are missing a newline here to maintain the current format (i.e "%llu\n"). > + > static int zswap_debugfs_init(void) > { > if (!debugfs_initialized()) > @@ -1732,8 +1728,8 @@ static int zswap_debugfs_init(void) > zswap_debugfs_root, &zswap_reject_compress_poor); > debugfs_create_u64("written_back_pages", 0444, > zswap_debugfs_root, &zswap_written_back_pages); > - debugfs_create_u64("pool_total_size", 0444, > - zswap_debugfs_root, &zswap_pool_total_size); > + debugfs_create_file("pool_total_size", 0444, > + zswap_debugfs_root, NULL, &total_size_fops); > debugfs_create_atomic_t("stored_pages", 0444, > zswap_debugfs_root, &zswap_stored_pages); > debugfs_create_atomic_t("same_filled_pages", 0444, > -- > 2.44.0 >
On Mon, Mar 11, 2024 at 10:09:35PM +0000, Yosry Ahmed wrote: > On Mon, Mar 11, 2024 at 12:12:13PM -0400, Johannes Weiner wrote: > > Profiling the munmap() of a zswapped memory region shows 50%(!) of the > > total cycles currently going into updating the zswap_pool_total_size. > > Yikes. I have always hated that size update scheme FWIW. > > I have also wondered whether it makes sense to just maintain the number > of pages in zswap as an atomic, like zswap_stored_pages. I guess your > proposed scheme is even cheaper for the load/invalidate paths because we > do nothing at all. It could be an option if the aggregation in other > paths ever becomes a problem, but we would need to make sure it > doesn't regress the load/invalidate paths. Just sharing some thoughts. Agree with you there. I actually tried doing it that way at first, but noticed zram uses zs_get_total_pages() and actually wants a per-pool count. I didn't want the backend to have to update two atomics, so I settled for this version. > > There are three consumers of this counter: > > - store, to enforce the globally configured pool limit > > - meminfo & debugfs, to report the size to the user > > - shrink, to determine the batch size for each cycle > > > > Instead of aggregating everytime an entry enters or exits the zswap > > pool, aggregate the value from the zpools on-demand: > > > > - Stores aggregate the counter anyway upon success. Aggregating to > > check the limit instead is the same amount of work. > > > > - Meminfo & debugfs might benefit somewhat from a pre-aggregated > > counter, but aren't exactly hotpaths. > > > > - Shrinking can aggregate once for every cycle instead of doing it for > > every freed entry. As the shrinker might work on tens or hundreds of > > objects per scan cycle, this is a large reduction in aggregations. > > > > The paths that benefit dramatically are swapin, swapoff, and > > unmaps. There could be millions of pages being processed until > > somebody asks for the pool size again. This eliminates the pool size > > updates from those paths entirely. > > This looks like a big win, thanks! I wonder if you have any numbers of > perf profiles to share. That would be nice to have, but I think the > benefit is clear regardless. I deleted the perf files already, but can re-run it tomorrow. > I also like the implicit cleanup when we switch to maintaining the > number of pages rather than bytes. The code looks much better with all > the shifts and divisions gone :) > > I have a couple of comments below. With them addressed, feel free to > add: > Acked-by: Yosry Ahmed <yosryahmed@google.com> Thanks! > > @@ -1385,6 +1365,10 @@ static void shrink_worker(struct work_struct *w) > > { > > struct mem_cgroup *memcg; > > int ret, failures = 0; > > + unsigned long thr; > > + > > + /* Reclaim down to the accept threshold */ > > + thr = zswap_max_pages() * zswap_accept_thr_percent / 100; > > This calculation is repeated twice, so I'd rather keep a helper for it > as an alternative to zswap_can_accept(). Perhaps zswap_threshold_page() > or zswap_acceptance_pages()? Sounds good. I went with zswap_accept_thr_pages(). > > @@ -1711,6 +1700,13 @@ void zswap_swapoff(int type) > > > > static struct dentry *zswap_debugfs_root; > > > > +static int debugfs_get_total_size(void *data, u64 *val) > > +{ > > + *val = zswap_total_pages() * PAGE_SIZE; > > + return 0; > > +} > > +DEFINE_DEBUGFS_ATTRIBUTE(total_size_fops, debugfs_get_total_size, NULL, "%llu"); > > I think we are missing a newline here to maintain the current format > (i.e "%llu\n"). Oops, good catch! I had verified the debugfs file (along with the others) with 'grep . *', which hides that this is missing. Fixed up. Thanks for taking a look. The incremental diff is below. I'll run the tests and recapture the numbers tomorrow, then send v2. diff --git a/mm/zswap.c b/mm/zswap.c index 7c39327a7cc2..1a5cc7298306 100644 --- a/mm/zswap.c +++ b/mm/zswap.c @@ -504,6 +504,11 @@ static unsigned long zswap_max_pages(void) return totalram_pages() * zswap_max_pool_percent / 100; } +static unsigned long zswap_accept_thr_pages(void) +{ + return zswap_max_pages() * zswap_accept_thr_percent / 100; +} + unsigned long zswap_total_pages(void) { struct zswap_pool *pool; @@ -1368,7 +1373,7 @@ static void shrink_worker(struct work_struct *w) unsigned long thr; /* Reclaim down to the accept threshold */ - thr = zswap_max_pages() * zswap_accept_thr_percent / 100; + thr = zswap_accept_thr_pages(); /* global reclaim will select cgroup in a round-robin fashion. */ do { @@ -1493,9 +1498,7 @@ bool zswap_store(struct folio *folio) } if (zswap_pool_reached_full) { - unsigned long thr = max_pages * zswap_accept_thr_percent / 100; - - if (cur_pages > thr) + if (cur_pages > zswap_accept_thr_pages()) goto shrink; else zswap_pool_reached_full = false; @@ -1705,7 +1708,7 @@ static int debugfs_get_total_size(void *data, u64 *val) *val = zswap_total_pages() * PAGE_SIZE; return 0; } -DEFINE_DEBUGFS_ATTRIBUTE(total_size_fops, debugfs_get_total_size, NULL, "%llu"); +DEFINE_DEBUGFS_ATTRIBUTE(total_size_fops, debugfs_get_total_size, NULL, "%llu\n"); static int zswap_debugfs_init(void) {
On Mon, Mar 11, 2024 at 10:34:11PM -0400, Johannes Weiner wrote: > On Mon, Mar 11, 2024 at 10:09:35PM +0000, Yosry Ahmed wrote: > > On Mon, Mar 11, 2024 at 12:12:13PM -0400, Johannes Weiner wrote: > > > Profiling the munmap() of a zswapped memory region shows 50%(!) of the > > > total cycles currently going into updating the zswap_pool_total_size. > > > > Yikes. I have always hated that size update scheme FWIW. > > > > I have also wondered whether it makes sense to just maintain the number > > of pages in zswap as an atomic, like zswap_stored_pages. I guess your > > proposed scheme is even cheaper for the load/invalidate paths because we > > do nothing at all. It could be an option if the aggregation in other > > paths ever becomes a problem, but we would need to make sure it > > doesn't regress the load/invalidate paths. Just sharing some thoughts. > > Agree with you there. I actually tried doing it that way at first, but > noticed zram uses zs_get_total_pages() and actually wants a per-pool > count. I didn't want the backend to have to update two atomics, so I > settled for this version. Could be useful to document this context if you send a v2. This version is a big improvement anyway, so hopefully we don' t need to revisit. > > > > There are three consumers of this counter: > > > - store, to enforce the globally configured pool limit > > > - meminfo & debugfs, to report the size to the user > > > - shrink, to determine the batch size for each cycle > > > > > > Instead of aggregating everytime an entry enters or exits the zswap > > > pool, aggregate the value from the zpools on-demand: > > > > > > - Stores aggregate the counter anyway upon success. Aggregating to > > > check the limit instead is the same amount of work. > > > > > > - Meminfo & debugfs might benefit somewhat from a pre-aggregated > > > counter, but aren't exactly hotpaths. > > > > > > - Shrinking can aggregate once for every cycle instead of doing it for > > > every freed entry. As the shrinker might work on tens or hundreds of > > > objects per scan cycle, this is a large reduction in aggregations. > > > > > > The paths that benefit dramatically are swapin, swapoff, and > > > unmaps. There could be millions of pages being processed until > > > somebody asks for the pool size again. This eliminates the pool size > > > updates from those paths entirely. > > > > This looks like a big win, thanks! I wonder if you have any numbers of > > perf profiles to share. That would be nice to have, but I think the > > benefit is clear regardless. > > I deleted the perf files already, but can re-run it tomorrow. Thanks! > > > I also like the implicit cleanup when we switch to maintaining the > > number of pages rather than bytes. The code looks much better with all > > the shifts and divisions gone :) > > > > I have a couple of comments below. With them addressed, feel free to > > add: > > Acked-by: Yosry Ahmed <yosryahmed@google.com> > > Thanks! > > > > @@ -1385,6 +1365,10 @@ static void shrink_worker(struct work_struct *w) > > > { > > > struct mem_cgroup *memcg; > > > int ret, failures = 0; > > > + unsigned long thr; > > > + > > > + /* Reclaim down to the accept threshold */ > > > + thr = zswap_max_pages() * zswap_accept_thr_percent / 100; > > > > This calculation is repeated twice, so I'd rather keep a helper for it > > as an alternative to zswap_can_accept(). Perhaps zswap_threshold_page() > > or zswap_acceptance_pages()? > > Sounds good. I went with zswap_accept_thr_pages(). Even better. > > > > @@ -1711,6 +1700,13 @@ void zswap_swapoff(int type) > > > > > > static struct dentry *zswap_debugfs_root; > > > > > > +static int debugfs_get_total_size(void *data, u64 *val) > > > +{ > > > + *val = zswap_total_pages() * PAGE_SIZE; > > > + return 0; > > > +} > > > +DEFINE_DEBUGFS_ATTRIBUTE(total_size_fops, debugfs_get_total_size, NULL, "%llu"); > > > > I think we are missing a newline here to maintain the current format > > (i.e "%llu\n"). > > Oops, good catch! I had verified the debugfs file (along with the > others) with 'grep . *', which hides that this is missing. Fixed up. > > Thanks for taking a look. The incremental diff is below. I'll run the > tests and recapture the numbers tomorrow, then send v2. LGTM. Feel free to carry the Ack forward.
On 2024/3/12 00:12, Johannes Weiner wrote: > Profiling the munmap() of a zswapped memory region shows 50%(!) of the > total cycles currently going into updating the zswap_pool_total_size. > > There are three consumers of this counter: > - store, to enforce the globally configured pool limit > - meminfo & debugfs, to report the size to the user > - shrink, to determine the batch size for each cycle > > Instead of aggregating everytime an entry enters or exits the zswap > pool, aggregate the value from the zpools on-demand: > > - Stores aggregate the counter anyway upon success. Aggregating to > check the limit instead is the same amount of work. > > - Meminfo & debugfs might benefit somewhat from a pre-aggregated > counter, but aren't exactly hotpaths. > > - Shrinking can aggregate once for every cycle instead of doing it for > every freed entry. As the shrinker might work on tens or hundreds of > objects per scan cycle, this is a large reduction in aggregations. > > The paths that benefit dramatically are swapin, swapoff, and > unmaps. There could be millions of pages being processed until > somebody asks for the pool size again. This eliminates the pool size > updates from those paths entirely. > > Signed-off-by: Johannes Weiner <hannes@cmpxchg.org> Great! This is a clever simplification and optimization. With the incremental diff, feel free to add: Reviewed-by: Chengming Zhou <chengming.zhou@linux.dev> Thanks. > --- > fs/proc/meminfo.c | 3 +- > include/linux/zswap.h | 2 +- > mm/zswap.c | 98 +++++++++++++++++++++---------------------- > 3 files changed, 49 insertions(+), 54 deletions(-) > > diff --git a/fs/proc/meminfo.c b/fs/proc/meminfo.c > index 45af9a989d40..245171d9164b 100644 > --- a/fs/proc/meminfo.c > +++ b/fs/proc/meminfo.c > @@ -89,8 +89,7 @@ static int meminfo_proc_show(struct seq_file *m, void *v) > show_val_kb(m, "SwapTotal: ", i.totalswap); > show_val_kb(m, "SwapFree: ", i.freeswap); > #ifdef CONFIG_ZSWAP > - seq_printf(m, "Zswap: %8lu kB\n", > - (unsigned long)(zswap_pool_total_size >> 10)); > + show_val_kb(m, "Zswap: ", zswap_total_pages()); > seq_printf(m, "Zswapped: %8lu kB\n", > (unsigned long)atomic_read(&zswap_stored_pages) << > (PAGE_SHIFT - 10)); > diff --git a/include/linux/zswap.h b/include/linux/zswap.h > index 341aea490070..2a85b941db97 100644 > --- a/include/linux/zswap.h > +++ b/include/linux/zswap.h > @@ -7,7 +7,6 @@ > > struct lruvec; > > -extern u64 zswap_pool_total_size; > extern atomic_t zswap_stored_pages; > > #ifdef CONFIG_ZSWAP > @@ -27,6 +26,7 @@ struct zswap_lruvec_state { > atomic_long_t nr_zswap_protected; > }; > > +unsigned long zswap_total_pages(void); > bool zswap_store(struct folio *folio); > bool zswap_load(struct folio *folio); > void zswap_invalidate(swp_entry_t swp); > diff --git a/mm/zswap.c b/mm/zswap.c > index 9a3237752082..7c39327a7cc2 100644 > --- a/mm/zswap.c > +++ b/mm/zswap.c > @@ -43,8 +43,6 @@ > /********************************* > * statistics > **********************************/ > -/* Total bytes used by the compressed storage */ > -u64 zswap_pool_total_size; > /* The number of compressed pages currently stored in zswap */ > atomic_t zswap_stored_pages = ATOMIC_INIT(0); > /* The number of same-value filled pages currently stored in zswap */ > @@ -264,45 +262,6 @@ static inline struct zswap_tree *swap_zswap_tree(swp_entry_t swp) > pr_debug("%s pool %s/%s\n", msg, (p)->tfm_name, \ > zpool_get_type((p)->zpools[0])) > > -static bool zswap_is_full(void) > -{ > - return totalram_pages() * zswap_max_pool_percent / 100 < > - DIV_ROUND_UP(zswap_pool_total_size, PAGE_SIZE); > -} > - > -static bool zswap_can_accept(void) > -{ > - return totalram_pages() * zswap_accept_thr_percent / 100 * > - zswap_max_pool_percent / 100 > > - DIV_ROUND_UP(zswap_pool_total_size, PAGE_SIZE); > -} > - > -static u64 get_zswap_pool_size(struct zswap_pool *pool) > -{ > - u64 pool_size = 0; > - int i; > - > - for (i = 0; i < ZSWAP_NR_ZPOOLS; i++) > - pool_size += zpool_get_total_size(pool->zpools[i]); > - > - return pool_size; > -} > - > -static void zswap_update_total_size(void) > -{ > - struct zswap_pool *pool; > - u64 total = 0; > - > - rcu_read_lock(); > - > - list_for_each_entry_rcu(pool, &zswap_pools, list) > - total += get_zswap_pool_size(pool); > - > - rcu_read_unlock(); > - > - zswap_pool_total_size = total; > -} > - > /********************************* > * pool functions > **********************************/ > @@ -540,6 +499,28 @@ static struct zswap_pool *zswap_pool_find_get(char *type, char *compressor) > return NULL; > } > > +static unsigned long zswap_max_pages(void) > +{ > + return totalram_pages() * zswap_max_pool_percent / 100; > +} > + > +unsigned long zswap_total_pages(void) > +{ > + struct zswap_pool *pool; > + u64 total = 0; > + > + rcu_read_lock(); > + list_for_each_entry_rcu(pool, &zswap_pools, list) { > + int i; > + > + for (i = 0; i < ZSWAP_NR_ZPOOLS; i++) > + total += zpool_get_total_size(pool->zpools[i]); > + } > + rcu_read_unlock(); > + > + return total >> PAGE_SHIFT; > +} > + > /********************************* > * param callbacks > **********************************/ > @@ -912,7 +893,6 @@ static void zswap_entry_free(struct zswap_entry *entry) > } > zswap_entry_cache_free(entry); > atomic_dec(&zswap_stored_pages); > - zswap_update_total_size(); > } > > /* > @@ -1317,7 +1297,7 @@ static unsigned long zswap_shrinker_count(struct shrinker *shrinker, > nr_stored = memcg_page_state(memcg, MEMCG_ZSWAPPED); > #else > /* use pool stats instead of memcg stats */ > - nr_backing = zswap_pool_total_size >> PAGE_SHIFT; > + nr_backing = zswap_total_pages(); > nr_stored = atomic_read(&zswap_nr_stored); > #endif > > @@ -1385,6 +1365,10 @@ static void shrink_worker(struct work_struct *w) > { > struct mem_cgroup *memcg; > int ret, failures = 0; > + unsigned long thr; > + > + /* Reclaim down to the accept threshold */ > + thr = zswap_max_pages() * zswap_accept_thr_percent / 100; > > /* global reclaim will select cgroup in a round-robin fashion. */ > do { > @@ -1432,10 +1416,9 @@ static void shrink_worker(struct work_struct *w) > break; > if (ret && ++failures == MAX_RECLAIM_RETRIES) > break; > - > resched: > cond_resched(); > - } while (!zswap_can_accept()); > + } while (zswap_total_pages() > thr); > } > > static int zswap_is_page_same_filled(void *ptr, unsigned long *value) > @@ -1476,6 +1459,7 @@ bool zswap_store(struct folio *folio) > struct zswap_entry *entry, *dupentry; > struct obj_cgroup *objcg = NULL; > struct mem_cgroup *memcg = NULL; > + unsigned long max_pages, cur_pages; > > VM_WARN_ON_ONCE(!folio_test_locked(folio)); > VM_WARN_ON_ONCE(!folio_test_swapcache(folio)); > @@ -1487,6 +1471,7 @@ bool zswap_store(struct folio *folio) > if (!zswap_enabled) > goto check_old; > > + /* Check cgroup limits */ > objcg = get_obj_cgroup_from_folio(folio); > if (objcg && !obj_cgroup_may_zswap(objcg)) { > memcg = get_mem_cgroup_from_objcg(objcg); > @@ -1497,15 +1482,20 @@ bool zswap_store(struct folio *folio) > mem_cgroup_put(memcg); > } > > - /* reclaim space if needed */ > - if (zswap_is_full()) { > + /* Check global limits */ > + cur_pages = zswap_total_pages(); > + max_pages = zswap_max_pages(); > + > + if (cur_pages >= max_pages) { > zswap_pool_limit_hit++; > zswap_pool_reached_full = true; > goto shrink; > } > > if (zswap_pool_reached_full) { > - if (!zswap_can_accept()) > + unsigned long thr = max_pages * zswap_accept_thr_percent / 100; > + > + if (cur_pages > thr) > goto shrink; > else > zswap_pool_reached_full = false; > @@ -1581,7 +1571,6 @@ bool zswap_store(struct folio *folio) > > /* update stats */ > atomic_inc(&zswap_stored_pages); > - zswap_update_total_size(); > count_vm_event(ZSWPOUT); > > return true; > @@ -1711,6 +1700,13 @@ void zswap_swapoff(int type) > > static struct dentry *zswap_debugfs_root; > > +static int debugfs_get_total_size(void *data, u64 *val) > +{ > + *val = zswap_total_pages() * PAGE_SIZE; > + return 0; > +} > +DEFINE_DEBUGFS_ATTRIBUTE(total_size_fops, debugfs_get_total_size, NULL, "%llu"); > + > static int zswap_debugfs_init(void) > { > if (!debugfs_initialized()) > @@ -1732,8 +1728,8 @@ static int zswap_debugfs_init(void) > zswap_debugfs_root, &zswap_reject_compress_poor); > debugfs_create_u64("written_back_pages", 0444, > zswap_debugfs_root, &zswap_written_back_pages); > - debugfs_create_u64("pool_total_size", 0444, > - zswap_debugfs_root, &zswap_pool_total_size); > + debugfs_create_file("pool_total_size", 0444, > + zswap_debugfs_root, NULL, &total_size_fops); > debugfs_create_atomic_t("stored_pages", 0444, > zswap_debugfs_root, &zswap_stored_pages); > debugfs_create_atomic_t("same_filled_pages", 0444,
On Mon, Mar 11, 2024 at 11:12 PM Johannes Weiner <hannes@cmpxchg.org> wrote: > > Profiling the munmap() of a zswapped memory region shows 50%(!) of the > total cycles currently going into updating the zswap_pool_total_size. > > There are three consumers of this counter: > - store, to enforce the globally configured pool limit > - meminfo & debugfs, to report the size to the user > - shrink, to determine the batch size for each cycle > > Instead of aggregating everytime an entry enters or exits the zswap > pool, aggregate the value from the zpools on-demand: > > - Stores aggregate the counter anyway upon success. Aggregating to > check the limit instead is the same amount of work. > > - Meminfo & debugfs might benefit somewhat from a pre-aggregated > counter, but aren't exactly hotpaths. > > - Shrinking can aggregate once for every cycle instead of doing it for > every freed entry. As the shrinker might work on tens or hundreds of > objects per scan cycle, this is a large reduction in aggregations. Nice! > > The paths that benefit dramatically are swapin, swapoff, and > unmaps. There could be millions of pages being processed until > somebody asks for the pool size again. This eliminates the pool size > updates from those paths entirely. > > Signed-off-by: Johannes Weiner <hannes@cmpxchg.org> With your fixlet applied: Reviewed-by: Nhat Pham <nphamcs@gmail.com> > --- > fs/proc/meminfo.c | 3 +- > include/linux/zswap.h | 2 +- > mm/zswap.c | 98 +++++++++++++++++++++---------------------- > 3 files changed, 49 insertions(+), 54 deletions(-) > > diff --git a/fs/proc/meminfo.c b/fs/proc/meminfo.c > index 45af9a989d40..245171d9164b 100644 > --- a/fs/proc/meminfo.c > +++ b/fs/proc/meminfo.c > @@ -89,8 +89,7 @@ static int meminfo_proc_show(struct seq_file *m, void *v) > show_val_kb(m, "SwapTotal: ", i.totalswap); > show_val_kb(m, "SwapFree: ", i.freeswap); > #ifdef CONFIG_ZSWAP > - seq_printf(m, "Zswap: %8lu kB\n", > - (unsigned long)(zswap_pool_total_size >> 10)); > + show_val_kb(m, "Zswap: ", zswap_total_pages()); > seq_printf(m, "Zswapped: %8lu kB\n", > (unsigned long)atomic_read(&zswap_stored_pages) << > (PAGE_SHIFT - 10)); > diff --git a/include/linux/zswap.h b/include/linux/zswap.h > index 341aea490070..2a85b941db97 100644 > --- a/include/linux/zswap.h > +++ b/include/linux/zswap.h > @@ -7,7 +7,6 @@ > > struct lruvec; > > -extern u64 zswap_pool_total_size; > extern atomic_t zswap_stored_pages; > > #ifdef CONFIG_ZSWAP > @@ -27,6 +26,7 @@ struct zswap_lruvec_state { > atomic_long_t nr_zswap_protected; > }; > > +unsigned long zswap_total_pages(void); > bool zswap_store(struct folio *folio); > bool zswap_load(struct folio *folio); > void zswap_invalidate(swp_entry_t swp); > diff --git a/mm/zswap.c b/mm/zswap.c > index 9a3237752082..7c39327a7cc2 100644 > --- a/mm/zswap.c > +++ b/mm/zswap.c > @@ -43,8 +43,6 @@ > /********************************* > * statistics > **********************************/ > -/* Total bytes used by the compressed storage */ > -u64 zswap_pool_total_size; > /* The number of compressed pages currently stored in zswap */ > atomic_t zswap_stored_pages = ATOMIC_INIT(0); > /* The number of same-value filled pages currently stored in zswap */ > @@ -264,45 +262,6 @@ static inline struct zswap_tree *swap_zswap_tree(swp_entry_t swp) > pr_debug("%s pool %s/%s\n", msg, (p)->tfm_name, \ > zpool_get_type((p)->zpools[0])) > > -static bool zswap_is_full(void) > -{ > - return totalram_pages() * zswap_max_pool_percent / 100 < > - DIV_ROUND_UP(zswap_pool_total_size, PAGE_SIZE); > -} > - > -static bool zswap_can_accept(void) > -{ > - return totalram_pages() * zswap_accept_thr_percent / 100 * > - zswap_max_pool_percent / 100 > > - DIV_ROUND_UP(zswap_pool_total_size, PAGE_SIZE); > -} > - > -static u64 get_zswap_pool_size(struct zswap_pool *pool) > -{ > - u64 pool_size = 0; > - int i; > - > - for (i = 0; i < ZSWAP_NR_ZPOOLS; i++) > - pool_size += zpool_get_total_size(pool->zpools[i]); > - > - return pool_size; > -} > - > -static void zswap_update_total_size(void) > -{ > - struct zswap_pool *pool; > - u64 total = 0; > - > - rcu_read_lock(); > - > - list_for_each_entry_rcu(pool, &zswap_pools, list) > - total += get_zswap_pool_size(pool); > - > - rcu_read_unlock(); > - > - zswap_pool_total_size = total; > -} > - > /********************************* > * pool functions > **********************************/ > @@ -540,6 +499,28 @@ static struct zswap_pool *zswap_pool_find_get(char *type, char *compressor) > return NULL; > } > > +static unsigned long zswap_max_pages(void) > +{ > + return totalram_pages() * zswap_max_pool_percent / 100; > +} > + > +unsigned long zswap_total_pages(void) > +{ > + struct zswap_pool *pool; > + u64 total = 0; > + > + rcu_read_lock(); > + list_for_each_entry_rcu(pool, &zswap_pools, list) { > + int i; > + > + for (i = 0; i < ZSWAP_NR_ZPOOLS; i++) > + total += zpool_get_total_size(pool->zpools[i]); > + } > + rcu_read_unlock(); > + > + return total >> PAGE_SHIFT; > +} > + > /********************************* > * param callbacks > **********************************/ > @@ -912,7 +893,6 @@ static void zswap_entry_free(struct zswap_entry *entry) > } > zswap_entry_cache_free(entry); > atomic_dec(&zswap_stored_pages); > - zswap_update_total_size(); > } > > /* > @@ -1317,7 +1297,7 @@ static unsigned long zswap_shrinker_count(struct shrinker *shrinker, > nr_stored = memcg_page_state(memcg, MEMCG_ZSWAPPED); > #else > /* use pool stats instead of memcg stats */ > - nr_backing = zswap_pool_total_size >> PAGE_SHIFT; > + nr_backing = zswap_total_pages(); > nr_stored = atomic_read(&zswap_nr_stored); > #endif > > @@ -1385,6 +1365,10 @@ static void shrink_worker(struct work_struct *w) > { > struct mem_cgroup *memcg; > int ret, failures = 0; > + unsigned long thr; > + > + /* Reclaim down to the accept threshold */ > + thr = zswap_max_pages() * zswap_accept_thr_percent / 100; > > /* global reclaim will select cgroup in a round-robin fashion. */ > do { > @@ -1432,10 +1416,9 @@ static void shrink_worker(struct work_struct *w) > break; > if (ret && ++failures == MAX_RECLAIM_RETRIES) > break; > - > resched: > cond_resched(); > - } while (!zswap_can_accept()); > + } while (zswap_total_pages() > thr); > } > > static int zswap_is_page_same_filled(void *ptr, unsigned long *value) > @@ -1476,6 +1459,7 @@ bool zswap_store(struct folio *folio) > struct zswap_entry *entry, *dupentry; > struct obj_cgroup *objcg = NULL; > struct mem_cgroup *memcg = NULL; > + unsigned long max_pages, cur_pages; > > VM_WARN_ON_ONCE(!folio_test_locked(folio)); > VM_WARN_ON_ONCE(!folio_test_swapcache(folio)); > @@ -1487,6 +1471,7 @@ bool zswap_store(struct folio *folio) > if (!zswap_enabled) > goto check_old; > > + /* Check cgroup limits */ > objcg = get_obj_cgroup_from_folio(folio); > if (objcg && !obj_cgroup_may_zswap(objcg)) { > memcg = get_mem_cgroup_from_objcg(objcg); > @@ -1497,15 +1482,20 @@ bool zswap_store(struct folio *folio) > mem_cgroup_put(memcg); > } > > - /* reclaim space if needed */ > - if (zswap_is_full()) { > + /* Check global limits */ > + cur_pages = zswap_total_pages(); > + max_pages = zswap_max_pages(); > + > + if (cur_pages >= max_pages) { > zswap_pool_limit_hit++; > zswap_pool_reached_full = true; > goto shrink; > } > > if (zswap_pool_reached_full) { > - if (!zswap_can_accept()) > + unsigned long thr = max_pages * zswap_accept_thr_percent / 100; > + > + if (cur_pages > thr) > goto shrink; > else > zswap_pool_reached_full = false; > @@ -1581,7 +1571,6 @@ bool zswap_store(struct folio *folio) > > /* update stats */ > atomic_inc(&zswap_stored_pages); > - zswap_update_total_size(); > count_vm_event(ZSWPOUT); > > return true; > @@ -1711,6 +1700,13 @@ void zswap_swapoff(int type) > > static struct dentry *zswap_debugfs_root; > > +static int debugfs_get_total_size(void *data, u64 *val) > +{ > + *val = zswap_total_pages() * PAGE_SIZE; > + return 0; > +} > +DEFINE_DEBUGFS_ATTRIBUTE(total_size_fops, debugfs_get_total_size, NULL, "%llu"); > + > static int zswap_debugfs_init(void) > { > if (!debugfs_initialized()) > @@ -1732,8 +1728,8 @@ static int zswap_debugfs_init(void) > zswap_debugfs_root, &zswap_reject_compress_poor); > debugfs_create_u64("written_back_pages", 0444, > zswap_debugfs_root, &zswap_written_back_pages); > - debugfs_create_u64("pool_total_size", 0444, > - zswap_debugfs_root, &zswap_pool_total_size); > + debugfs_create_file("pool_total_size", 0444, > + zswap_debugfs_root, NULL, &total_size_fops); > debugfs_create_atomic_t("stored_pages", 0444, > zswap_debugfs_root, &zswap_stored_pages); > debugfs_create_atomic_t("same_filled_pages", 0444, > -- > 2.44.0 >
diff --git a/fs/proc/meminfo.c b/fs/proc/meminfo.c index 45af9a989d40..245171d9164b 100644 --- a/fs/proc/meminfo.c +++ b/fs/proc/meminfo.c @@ -89,8 +89,7 @@ static int meminfo_proc_show(struct seq_file *m, void *v) show_val_kb(m, "SwapTotal: ", i.totalswap); show_val_kb(m, "SwapFree: ", i.freeswap); #ifdef CONFIG_ZSWAP - seq_printf(m, "Zswap: %8lu kB\n", - (unsigned long)(zswap_pool_total_size >> 10)); + show_val_kb(m, "Zswap: ", zswap_total_pages()); seq_printf(m, "Zswapped: %8lu kB\n", (unsigned long)atomic_read(&zswap_stored_pages) << (PAGE_SHIFT - 10)); diff --git a/include/linux/zswap.h b/include/linux/zswap.h index 341aea490070..2a85b941db97 100644 --- a/include/linux/zswap.h +++ b/include/linux/zswap.h @@ -7,7 +7,6 @@ struct lruvec; -extern u64 zswap_pool_total_size; extern atomic_t zswap_stored_pages; #ifdef CONFIG_ZSWAP @@ -27,6 +26,7 @@ struct zswap_lruvec_state { atomic_long_t nr_zswap_protected; }; +unsigned long zswap_total_pages(void); bool zswap_store(struct folio *folio); bool zswap_load(struct folio *folio); void zswap_invalidate(swp_entry_t swp); diff --git a/mm/zswap.c b/mm/zswap.c index 9a3237752082..7c39327a7cc2 100644 --- a/mm/zswap.c +++ b/mm/zswap.c @@ -43,8 +43,6 @@ /********************************* * statistics **********************************/ -/* Total bytes used by the compressed storage */ -u64 zswap_pool_total_size; /* The number of compressed pages currently stored in zswap */ atomic_t zswap_stored_pages = ATOMIC_INIT(0); /* The number of same-value filled pages currently stored in zswap */ @@ -264,45 +262,6 @@ static inline struct zswap_tree *swap_zswap_tree(swp_entry_t swp) pr_debug("%s pool %s/%s\n", msg, (p)->tfm_name, \ zpool_get_type((p)->zpools[0])) -static bool zswap_is_full(void) -{ - return totalram_pages() * zswap_max_pool_percent / 100 < - DIV_ROUND_UP(zswap_pool_total_size, PAGE_SIZE); -} - -static bool zswap_can_accept(void) -{ - return totalram_pages() * zswap_accept_thr_percent / 100 * - zswap_max_pool_percent / 100 > - DIV_ROUND_UP(zswap_pool_total_size, PAGE_SIZE); -} - -static u64 get_zswap_pool_size(struct zswap_pool *pool) -{ - u64 pool_size = 0; - int i; - - for (i = 0; i < ZSWAP_NR_ZPOOLS; i++) - pool_size += zpool_get_total_size(pool->zpools[i]); - - return pool_size; -} - -static void zswap_update_total_size(void) -{ - struct zswap_pool *pool; - u64 total = 0; - - rcu_read_lock(); - - list_for_each_entry_rcu(pool, &zswap_pools, list) - total += get_zswap_pool_size(pool); - - rcu_read_unlock(); - - zswap_pool_total_size = total; -} - /********************************* * pool functions **********************************/ @@ -540,6 +499,28 @@ static struct zswap_pool *zswap_pool_find_get(char *type, char *compressor) return NULL; } +static unsigned long zswap_max_pages(void) +{ + return totalram_pages() * zswap_max_pool_percent / 100; +} + +unsigned long zswap_total_pages(void) +{ + struct zswap_pool *pool; + u64 total = 0; + + rcu_read_lock(); + list_for_each_entry_rcu(pool, &zswap_pools, list) { + int i; + + for (i = 0; i < ZSWAP_NR_ZPOOLS; i++) + total += zpool_get_total_size(pool->zpools[i]); + } + rcu_read_unlock(); + + return total >> PAGE_SHIFT; +} + /********************************* * param callbacks **********************************/ @@ -912,7 +893,6 @@ static void zswap_entry_free(struct zswap_entry *entry) } zswap_entry_cache_free(entry); atomic_dec(&zswap_stored_pages); - zswap_update_total_size(); } /* @@ -1317,7 +1297,7 @@ static unsigned long zswap_shrinker_count(struct shrinker *shrinker, nr_stored = memcg_page_state(memcg, MEMCG_ZSWAPPED); #else /* use pool stats instead of memcg stats */ - nr_backing = zswap_pool_total_size >> PAGE_SHIFT; + nr_backing = zswap_total_pages(); nr_stored = atomic_read(&zswap_nr_stored); #endif @@ -1385,6 +1365,10 @@ static void shrink_worker(struct work_struct *w) { struct mem_cgroup *memcg; int ret, failures = 0; + unsigned long thr; + + /* Reclaim down to the accept threshold */ + thr = zswap_max_pages() * zswap_accept_thr_percent / 100; /* global reclaim will select cgroup in a round-robin fashion. */ do { @@ -1432,10 +1416,9 @@ static void shrink_worker(struct work_struct *w) break; if (ret && ++failures == MAX_RECLAIM_RETRIES) break; - resched: cond_resched(); - } while (!zswap_can_accept()); + } while (zswap_total_pages() > thr); } static int zswap_is_page_same_filled(void *ptr, unsigned long *value) @@ -1476,6 +1459,7 @@ bool zswap_store(struct folio *folio) struct zswap_entry *entry, *dupentry; struct obj_cgroup *objcg = NULL; struct mem_cgroup *memcg = NULL; + unsigned long max_pages, cur_pages; VM_WARN_ON_ONCE(!folio_test_locked(folio)); VM_WARN_ON_ONCE(!folio_test_swapcache(folio)); @@ -1487,6 +1471,7 @@ bool zswap_store(struct folio *folio) if (!zswap_enabled) goto check_old; + /* Check cgroup limits */ objcg = get_obj_cgroup_from_folio(folio); if (objcg && !obj_cgroup_may_zswap(objcg)) { memcg = get_mem_cgroup_from_objcg(objcg); @@ -1497,15 +1482,20 @@ bool zswap_store(struct folio *folio) mem_cgroup_put(memcg); } - /* reclaim space if needed */ - if (zswap_is_full()) { + /* Check global limits */ + cur_pages = zswap_total_pages(); + max_pages = zswap_max_pages(); + + if (cur_pages >= max_pages) { zswap_pool_limit_hit++; zswap_pool_reached_full = true; goto shrink; } if (zswap_pool_reached_full) { - if (!zswap_can_accept()) + unsigned long thr = max_pages * zswap_accept_thr_percent / 100; + + if (cur_pages > thr) goto shrink; else zswap_pool_reached_full = false; @@ -1581,7 +1571,6 @@ bool zswap_store(struct folio *folio) /* update stats */ atomic_inc(&zswap_stored_pages); - zswap_update_total_size(); count_vm_event(ZSWPOUT); return true; @@ -1711,6 +1700,13 @@ void zswap_swapoff(int type) static struct dentry *zswap_debugfs_root; +static int debugfs_get_total_size(void *data, u64 *val) +{ + *val = zswap_total_pages() * PAGE_SIZE; + return 0; +} +DEFINE_DEBUGFS_ATTRIBUTE(total_size_fops, debugfs_get_total_size, NULL, "%llu"); + static int zswap_debugfs_init(void) { if (!debugfs_initialized()) @@ -1732,8 +1728,8 @@ static int zswap_debugfs_init(void) zswap_debugfs_root, &zswap_reject_compress_poor); debugfs_create_u64("written_back_pages", 0444, zswap_debugfs_root, &zswap_written_back_pages); - debugfs_create_u64("pool_total_size", 0444, - zswap_debugfs_root, &zswap_pool_total_size); + debugfs_create_file("pool_total_size", 0444, + zswap_debugfs_root, NULL, &total_size_fops); debugfs_create_atomic_t("stored_pages", 0444, zswap_debugfs_root, &zswap_stored_pages); debugfs_create_atomic_t("same_filled_pages", 0444,
Profiling the munmap() of a zswapped memory region shows 50%(!) of the total cycles currently going into updating the zswap_pool_total_size. There are three consumers of this counter: - store, to enforce the globally configured pool limit - meminfo & debugfs, to report the size to the user - shrink, to determine the batch size for each cycle Instead of aggregating everytime an entry enters or exits the zswap pool, aggregate the value from the zpools on-demand: - Stores aggregate the counter anyway upon success. Aggregating to check the limit instead is the same amount of work. - Meminfo & debugfs might benefit somewhat from a pre-aggregated counter, but aren't exactly hotpaths. - Shrinking can aggregate once for every cycle instead of doing it for every freed entry. As the shrinker might work on tens or hundreds of objects per scan cycle, this is a large reduction in aggregations. The paths that benefit dramatically are swapin, swapoff, and unmaps. There could be millions of pages being processed until somebody asks for the pool size again. This eliminates the pool size updates from those paths entirely. Signed-off-by: Johannes Weiner <hannes@cmpxchg.org> --- fs/proc/meminfo.c | 3 +- include/linux/zswap.h | 2 +- mm/zswap.c | 98 +++++++++++++++++++++---------------------- 3 files changed, 49 insertions(+), 54 deletions(-)