| Message ID | 20230405185427.1246289-3-yosryahmed@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Ignore non-LRU-based reclaim in memcg reclaim | expand |
On Wed, 2023-04-05 at 18:54 +0000, Yosry Ahmed wrote: > During reclaim, we keep track of pages reclaimed from other means than > LRU-based reclaim through scan_control->reclaim_state->reclaimed_slab, > which we stash a pointer to in current task_struct. > > However, we keep track of more than just reclaimed slab pages through > this. We also use it for clean file pages dropped through pruned inodes, > and xfs buffer pages freed. Rename reclaimed_slab to reclaimed, and add > a helper function that wraps updating it through current, so that future > changes to this logic are contained within mm/vmscan.c. > > Additionally, add a flush_reclaim_state() helper to wrap using > reclaim_state->reclaimed to updated sc->nr_reclaimed, and use that > helper to add an elaborate comment about why we only do the update for > global reclaim. > > Finally, move set_task_reclaim_state() next to flush_reclaim_state() so > that all reclaim_state helpers are in close proximity for easier > readability. > > Signed-off-by: Yosry Ahmed <yosryahmed@google.com> > --- > fs/inode.c | 3 +- > fs/xfs/xfs_buf.c | 3 +- > include/linux/swap.h | 17 +++++++++- > mm/slab.c | 3 +- > mm/slob.c | 6 ++-- > mm/slub.c | 5 ++- > mm/vmscan.c | 75 ++++++++++++++++++++++++++++++++------------ > 7 files changed, 78 insertions(+), 34 deletions(-) > > diff --git a/fs/inode.c b/fs/inode.c > index 4558dc2f13557..e60fcc41faf17 100644 > --- a/fs/inode.c > +++ b/fs/inode.c > @@ -864,8 +864,7 @@ static enum lru_status inode_lru_isolate(struct list_head *item, > __count_vm_events(KSWAPD_INODESTEAL, reap); > else > __count_vm_events(PGINODESTEAL, reap); > - if (current->reclaim_state) > - current->reclaim_state->reclaimed_slab += reap; > + mm_account_reclaimed_pages(reap); > } > iput(inode); > spin_lock(lru_lock); > diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c > index 54c774af6e1c6..15d1e5a7c2d34 100644 > --- a/fs/xfs/xfs_buf.c > +++ b/fs/xfs/xfs_buf.c > @@ -286,8 +286,7 @@ xfs_buf_free_pages( > if (bp->b_pages[i]) > __free_page(bp->b_pages[i]); > } > - if (current->reclaim_state) > - current->reclaim_state->reclaimed_slab += bp->b_page_count; > + mm_account_reclaimed_pages(bp->b_page_count); > > if (bp->b_pages != bp->b_page_array) > kmem_free(bp->b_pages); > diff --git a/include/linux/swap.h b/include/linux/swap.h > index 209a425739a9f..e131ac155fb95 100644 > --- a/include/linux/swap.h > +++ b/include/linux/swap.h > @@ -153,13 +153,28 @@ union swap_header { > * memory reclaim > */ > struct reclaim_state { > - unsigned long reclaimed_slab; > + /* pages reclaimed outside of LRU-based reclaim */ > + unsigned long reclaimed; > #ifdef CONFIG_LRU_GEN > /* per-thread mm walk data */ > struct lru_gen_mm_walk *mm_walk; > #endif > }; > > +/* > + * mm_account_reclaimed_pages(): account reclaimed pages outside of LRU-based > + * reclaim > + * @pages: number of pages reclaimed > + * > + * If the current process is undergoing a reclaim operation, increment the > + * number of reclaimed pages by @pages. > + */ > +static inline void mm_account_reclaimed_pages(unsigned long pages) > +{ > + if (current->reclaim_state) > + current->reclaim_state->reclaimed += pages; > +} > + > #ifdef __KERNEL__ > > struct address_space; > diff --git a/mm/slab.c b/mm/slab.c > index dabc2a671fc6f..64bf1de817b24 100644 > --- a/mm/slab.c > +++ b/mm/slab.c > @@ -1392,8 +1392,7 @@ static void kmem_freepages(struct kmem_cache *cachep, struct slab *slab) > smp_wmb(); > __folio_clear_slab(folio); > > - if (current->reclaim_state) > - current->reclaim_state->reclaimed_slab += 1 << order; > + mm_account_reclaimed_pages(1 << order); > unaccount_slab(slab, order, cachep); > __free_pages(&folio->page, order); > } > diff --git a/mm/slob.c b/mm/slob.c > index fe567fcfa3a39..79cc8680c973c 100644 > --- a/mm/slob.c > +++ b/mm/slob.c > @@ -61,7 +61,7 @@ > #include <linux/slab.h> > > #include <linux/mm.h> > -#include <linux/swap.h> /* struct reclaim_state */ > +#include <linux/swap.h> /* mm_account_reclaimed_pages() */ > #include <linux/cache.h> > #include <linux/init.h> > #include <linux/export.h> > @@ -211,9 +211,7 @@ static void slob_free_pages(void *b, int order) > { > struct page *sp = virt_to_page(b); > > - if (current->reclaim_state) > - current->reclaim_state->reclaimed_slab += 1 << order; > - > + mm_account_reclaimed_pages(1 << order); > mod_node_page_state(page_pgdat(sp), NR_SLAB_UNRECLAIMABLE_B, > -(PAGE_SIZE << order)); > __free_pages(sp, order); > diff --git a/mm/slub.c b/mm/slub.c > index 39327e98fce34..7aa30eef82350 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -11,7 +11,7 @@ > */ > > #include <linux/mm.h> > -#include <linux/swap.h> /* struct reclaim_state */ > +#include <linux/swap.h> /* mm_account_reclaimed_pages() */ > #include <linux/module.h> > #include <linux/bit_spinlock.h> > #include <linux/interrupt.h> > @@ -2063,8 +2063,7 @@ static void __free_slab(struct kmem_cache *s, struct slab *slab) > /* Make the mapping reset visible before clearing the flag */ > smp_wmb(); > __folio_clear_slab(folio); > - if (current->reclaim_state) > - current->reclaim_state->reclaimed_slab += pages; > + mm_account_reclaimed_pages(pages); > unaccount_slab(slab, order, s); > __free_pages(&folio->page, order); > } > diff --git a/mm/vmscan.c b/mm/vmscan.c > index c82bd89f90364..049e39202e6ce 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -188,18 +188,6 @@ struct scan_control { > */ > int vm_swappiness = 60; > > -static void set_task_reclaim_state(struct task_struct *task, > - struct reclaim_state *rs) > -{ > - /* Check for an overwrite */ > - WARN_ON_ONCE(rs && task->reclaim_state); > - > - /* Check for the nulling of an already-nulled member */ > - WARN_ON_ONCE(!rs && !task->reclaim_state); > - > - task->reclaim_state = rs; > -} > - > LIST_HEAD(shrinker_list); > DECLARE_RWSEM(shrinker_rwsem); > > @@ -511,6 +499,59 @@ static bool writeback_throttling_sane(struct scan_control *sc) > } > #endif > > +static void set_task_reclaim_state(struct task_struct *task, > + struct reclaim_state *rs) > +{ > + /* Check for an overwrite */ > + WARN_ON_ONCE(rs && task->reclaim_state); > + > + /* Check for the nulling of an already-nulled member */ > + WARN_ON_ONCE(!rs && !task->reclaim_state); > + > + task->reclaim_state = rs; > +} > + > +/* > + * flush_reclaim_state(): add pages reclaimed outside of LRU-based reclaim to > + * scan_control->nr_reclaimed. > + */ > +static void flush_reclaim_state(struct scan_control *sc, > + struct reclaim_state *rs) > +{ > + /* > + * Currently, reclaim_state->reclaimed includes three types of pages > + * freed outside of vmscan: > + * (1) Slab pages. > + * (2) Clean file pages from pruned inodes. > + * (3) XFS freed buffer pages. > + * > + * For all of these cases, we have no way of finding out whether these > + * pages were related to the memcg under reclaim. For example, a freed > + * slab page could have had only a single object charged to the memcg Minor nits: s/could have had/could have > + * under reclaim. Also, populated inodes are not on shrinker LRUs > + * anymore except on highmem systems. > + * > + * Instead of over-reporting the reclaimed pages in a memcg reclaim, > + * only count such pages in global reclaim. This prevents unnecessary May be clearer to say: This prevents under-reclaimaing the target memcg, and unnecessary > + * retries during memcg charging and false positive from proactive > + * reclaim (memory.reclaim). > + * Tim
On Thu, Apr 6, 2023 at 10:32 AM Tim Chen <tim.c.chen@linux.intel.com> wrote: > > On Wed, 2023-04-05 at 18:54 +0000, Yosry Ahmed wrote: > > During reclaim, we keep track of pages reclaimed from other means than > > LRU-based reclaim through scan_control->reclaim_state->reclaimed_slab, > > which we stash a pointer to in current task_struct. > > > > However, we keep track of more than just reclaimed slab pages through > > this. We also use it for clean file pages dropped through pruned inodes, > > and xfs buffer pages freed. Rename reclaimed_slab to reclaimed, and add > > a helper function that wraps updating it through current, so that future > > changes to this logic are contained within mm/vmscan.c. > > > > Additionally, add a flush_reclaim_state() helper to wrap using > > reclaim_state->reclaimed to updated sc->nr_reclaimed, and use that > > helper to add an elaborate comment about why we only do the update for > > global reclaim. > > > > Finally, move set_task_reclaim_state() next to flush_reclaim_state() so > > that all reclaim_state helpers are in close proximity for easier > > readability. > > > > Signed-off-by: Yosry Ahmed <yosryahmed@google.com> > > --- > > fs/inode.c | 3 +- > > fs/xfs/xfs_buf.c | 3 +- > > include/linux/swap.h | 17 +++++++++- > > mm/slab.c | 3 +- > > mm/slob.c | 6 ++-- > > mm/slub.c | 5 ++- > > mm/vmscan.c | 75 ++++++++++++++++++++++++++++++++------------ > > 7 files changed, 78 insertions(+), 34 deletions(-) > > > > diff --git a/fs/inode.c b/fs/inode.c > > index 4558dc2f13557..e60fcc41faf17 100644 > > --- a/fs/inode.c > > +++ b/fs/inode.c > > @@ -864,8 +864,7 @@ static enum lru_status inode_lru_isolate(struct list_head *item, > > __count_vm_events(KSWAPD_INODESTEAL, reap); > > else > > __count_vm_events(PGINODESTEAL, reap); > > - if (current->reclaim_state) > > - current->reclaim_state->reclaimed_slab += reap; > > + mm_account_reclaimed_pages(reap); > > } > > iput(inode); > > spin_lock(lru_lock); > > diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c > > index 54c774af6e1c6..15d1e5a7c2d34 100644 > > --- a/fs/xfs/xfs_buf.c > > +++ b/fs/xfs/xfs_buf.c > > @@ -286,8 +286,7 @@ xfs_buf_free_pages( > > if (bp->b_pages[i]) > > __free_page(bp->b_pages[i]); > > } > > - if (current->reclaim_state) > > - current->reclaim_state->reclaimed_slab += bp->b_page_count; > > + mm_account_reclaimed_pages(bp->b_page_count); > > > > if (bp->b_pages != bp->b_page_array) > > kmem_free(bp->b_pages); > > diff --git a/include/linux/swap.h b/include/linux/swap.h > > index 209a425739a9f..e131ac155fb95 100644 > > --- a/include/linux/swap.h > > +++ b/include/linux/swap.h > > @@ -153,13 +153,28 @@ union swap_header { > > * memory reclaim > > */ > > struct reclaim_state { > > - unsigned long reclaimed_slab; > > + /* pages reclaimed outside of LRU-based reclaim */ > > + unsigned long reclaimed; > > #ifdef CONFIG_LRU_GEN > > /* per-thread mm walk data */ > > struct lru_gen_mm_walk *mm_walk; > > #endif > > }; > > > > +/* > > + * mm_account_reclaimed_pages(): account reclaimed pages outside of LRU-based > > + * reclaim > > + * @pages: number of pages reclaimed > > + * > > + * If the current process is undergoing a reclaim operation, increment the > > + * number of reclaimed pages by @pages. > > + */ > > +static inline void mm_account_reclaimed_pages(unsigned long pages) > > +{ > > + if (current->reclaim_state) > > + current->reclaim_state->reclaimed += pages; > > +} > > + > > #ifdef __KERNEL__ > > > > struct address_space; > > diff --git a/mm/slab.c b/mm/slab.c > > index dabc2a671fc6f..64bf1de817b24 100644 > > --- a/mm/slab.c > > +++ b/mm/slab.c > > @@ -1392,8 +1392,7 @@ static void kmem_freepages(struct kmem_cache *cachep, struct slab *slab) > > smp_wmb(); > > __folio_clear_slab(folio); > > > > - if (current->reclaim_state) > > - current->reclaim_state->reclaimed_slab += 1 << order; > > + mm_account_reclaimed_pages(1 << order); > > unaccount_slab(slab, order, cachep); > > __free_pages(&folio->page, order); > > } > > diff --git a/mm/slob.c b/mm/slob.c > > index fe567fcfa3a39..79cc8680c973c 100644 > > --- a/mm/slob.c > > +++ b/mm/slob.c > > @@ -61,7 +61,7 @@ > > #include <linux/slab.h> > > > > #include <linux/mm.h> > > -#include <linux/swap.h> /* struct reclaim_state */ > > +#include <linux/swap.h> /* mm_account_reclaimed_pages() */ > > #include <linux/cache.h> > > #include <linux/init.h> > > #include <linux/export.h> > > @@ -211,9 +211,7 @@ static void slob_free_pages(void *b, int order) > > { > > struct page *sp = virt_to_page(b); > > > > - if (current->reclaim_state) > > - current->reclaim_state->reclaimed_slab += 1 << order; > > - > > + mm_account_reclaimed_pages(1 << order); > > mod_node_page_state(page_pgdat(sp), NR_SLAB_UNRECLAIMABLE_B, > > -(PAGE_SIZE << order)); > > __free_pages(sp, order); > > diff --git a/mm/slub.c b/mm/slub.c > > index 39327e98fce34..7aa30eef82350 100644 > > --- a/mm/slub.c > > +++ b/mm/slub.c > > @@ -11,7 +11,7 @@ > > */ > > > > #include <linux/mm.h> > > -#include <linux/swap.h> /* struct reclaim_state */ > > +#include <linux/swap.h> /* mm_account_reclaimed_pages() */ > > #include <linux/module.h> > > #include <linux/bit_spinlock.h> > > #include <linux/interrupt.h> > > @@ -2063,8 +2063,7 @@ static void __free_slab(struct kmem_cache *s, struct slab *slab) > > /* Make the mapping reset visible before clearing the flag */ > > smp_wmb(); > > __folio_clear_slab(folio); > > - if (current->reclaim_state) > > - current->reclaim_state->reclaimed_slab += pages; > > + mm_account_reclaimed_pages(pages); > > unaccount_slab(slab, order, s); > > __free_pages(&folio->page, order); > > } > > diff --git a/mm/vmscan.c b/mm/vmscan.c > > index c82bd89f90364..049e39202e6ce 100644 > > --- a/mm/vmscan.c > > +++ b/mm/vmscan.c > > @@ -188,18 +188,6 @@ struct scan_control { > > */ > > int vm_swappiness = 60; > > > > -static void set_task_reclaim_state(struct task_struct *task, > > - struct reclaim_state *rs) > > -{ > > - /* Check for an overwrite */ > > - WARN_ON_ONCE(rs && task->reclaim_state); > > - > > - /* Check for the nulling of an already-nulled member */ > > - WARN_ON_ONCE(!rs && !task->reclaim_state); > > - > > - task->reclaim_state = rs; > > -} > > - > > LIST_HEAD(shrinker_list); > > DECLARE_RWSEM(shrinker_rwsem); > > > > @@ -511,6 +499,59 @@ static bool writeback_throttling_sane(struct scan_control *sc) > > } > > #endif > > > > +static void set_task_reclaim_state(struct task_struct *task, > > + struct reclaim_state *rs) > > +{ > > + /* Check for an overwrite */ > > + WARN_ON_ONCE(rs && task->reclaim_state); > > + > > + /* Check for the nulling of an already-nulled member */ > > + WARN_ON_ONCE(!rs && !task->reclaim_state); > > + > > + task->reclaim_state = rs; > > +} > > + > > +/* > > + * flush_reclaim_state(): add pages reclaimed outside of LRU-based reclaim to > > + * scan_control->nr_reclaimed. > > + */ > > +static void flush_reclaim_state(struct scan_control *sc, > > + struct reclaim_state *rs) > > +{ > > + /* > > + * Currently, reclaim_state->reclaimed includes three types of pages > > + * freed outside of vmscan: > > + * (1) Slab pages. > > + * (2) Clean file pages from pruned inodes. > > + * (3) XFS freed buffer pages. > > + * > > + * For all of these cases, we have no way of finding out whether these > > + * pages were related to the memcg under reclaim. For example, a freed > > + * slab page could have had only a single object charged to the memcg > > Minor nits: > s/could have had/could have > > > + * under reclaim. Also, populated inodes are not on shrinker LRUs > > + * anymore except on highmem systems. > > + * > > + * Instead of over-reporting the reclaimed pages in a memcg reclaim, > > + * only count such pages in global reclaim. This prevents unnecessary > > May be clearer to say: > This prevents under-reclaimaing the target memcg, and unnecessary Thanks, will rephrase for the next version! > > > + * retries during memcg charging and false positive from proactive > > + * reclaim (memory.reclaim). > > + * > > Tim >
On Thu, Apr 06, 2023 at 10:31:53AM -0700, Tim Chen wrote: > On Wed, 2023-04-05 at 18:54 +0000, Yosry Ahmed wrote: > > + * For all of these cases, we have no way of finding out whether these > > + * pages were related to the memcg under reclaim. For example, a freed > > + * slab page could have had only a single object charged to the memcg > > Minor nits: > s/could have had/could have No ... "could have had" is correct. I'm a native English speaker, so I have no idea what the rule here is, but I can ask my linguist wife later if you want to know ;-) Maybe it's something like this: https://www.englishgrammar.org/have-had-and-had-had/
Hi, Yosry, On Wed, Apr 05, 2023 at 06:54:27PM +0000, Yosry Ahmed wrote: [...] > diff --git a/mm/vmscan.c b/mm/vmscan.c > index c82bd89f90364..049e39202e6ce 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -188,18 +188,6 @@ struct scan_control { > */ > int vm_swappiness = 60; > > -static void set_task_reclaim_state(struct task_struct *task, > - struct reclaim_state *rs) > -{ > - /* Check for an overwrite */ > - WARN_ON_ONCE(rs && task->reclaim_state); > - > - /* Check for the nulling of an already-nulled member */ > - WARN_ON_ONCE(!rs && !task->reclaim_state); > - > - task->reclaim_state = rs; > -} > - > LIST_HEAD(shrinker_list); > DECLARE_RWSEM(shrinker_rwsem); > > @@ -511,6 +499,59 @@ static bool writeback_throttling_sane(struct scan_control *sc) > } > #endif > > +static void set_task_reclaim_state(struct task_struct *task, > + struct reclaim_state *rs) > +{ > + /* Check for an overwrite */ > + WARN_ON_ONCE(rs && task->reclaim_state); > + > + /* Check for the nulling of an already-nulled member */ > + WARN_ON_ONCE(!rs && !task->reclaim_state); > + > + task->reclaim_state = rs; > +} Nit: I just think such movement not necessary while it loses the "git blame" information easily. Instead of moving this here without major benefit, why not just define flush_reclaim_state() right after previous set_task_reclaim_state()? > + > +/* > + * flush_reclaim_state(): add pages reclaimed outside of LRU-based reclaim to > + * scan_control->nr_reclaimed. > + */ > +static void flush_reclaim_state(struct scan_control *sc, > + struct reclaim_state *rs) > +{ > + /* > + * Currently, reclaim_state->reclaimed includes three types of pages > + * freed outside of vmscan: > + * (1) Slab pages. > + * (2) Clean file pages from pruned inodes. > + * (3) XFS freed buffer pages. > + * > + * For all of these cases, we have no way of finding out whether these > + * pages were related to the memcg under reclaim. For example, a freed > + * slab page could have had only a single object charged to the memcg > + * under reclaim. Also, populated inodes are not on shrinker LRUs > + * anymore except on highmem systems. > + * > + * Instead of over-reporting the reclaimed pages in a memcg reclaim, > + * only count such pages in global reclaim. This prevents unnecessary > + * retries during memcg charging and false positive from proactive > + * reclaim (memory.reclaim). > + * > + * For uncommon cases were the freed pages were actually significantly > + * charged to the memcg under reclaim, and we end up under-reporting, it > + * should be fine. The freed pages will be uncharged anyway, even if > + * they are not reported properly, and we will be able to make forward > + * progress in charging (which is usually in a retry loop). > + * > + * We can go one step further, and report the uncharged objcg pages in > + * memcg reclaim, to make reporting more accurate and reduce > + * under-reporting, but it's probably not worth the complexity for now. > + */ > + if (rs && global_reclaim(sc)) { > + sc->nr_reclaimed += rs->reclaimed; > + rs->reclaimed = 0; > + } > +} > + > static long xchg_nr_deferred(struct shrinker *shrinker, > struct shrink_control *sc) > { > @@ -5346,10 +5387,7 @@ static int shrink_one(struct lruvec *lruvec, struct scan_control *sc) > vmpressure(sc->gfp_mask, memcg, false, sc->nr_scanned - scanned, > sc->nr_reclaimed - reclaimed); > > - if (global_reclaim(sc)) { > - sc->nr_reclaimed += current->reclaim_state->reclaimed_slab; > - current->reclaim_state->reclaimed_slab = 0; > - } > + flush_reclaim_state(sc, current->reclaim_state); > > return success ? MEMCG_LRU_YOUNG : 0; > } > @@ -6474,10 +6512,7 @@ static void shrink_node(pg_data_t *pgdat, struct scan_control *sc) > > shrink_node_memcgs(pgdat, sc); > > - if (reclaim_state && global_reclaim(sc)) { > - sc->nr_reclaimed += reclaim_state->reclaimed_slab; > - reclaim_state->reclaimed_slab = 0; > - } > + flush_reclaim_state(sc, reclaim_state); IIUC reclaim_state here still points to current->reclaim_state. Could it change at all? Is it cleaner to make flush_reclaim_state() taking "sc" only if it always references current->reclaim_state? > > /* Record the subtree's reclaim efficiency */ > if (!sc->proactive) > -- > 2.40.0.348.gf938b09366-goog >
On Thu, Apr 6, 2023 at 1:45 PM Peter Xu <peterx@redhat.com> wrote: > > Hi, Yosry, > > On Wed, Apr 05, 2023 at 06:54:27PM +0000, Yosry Ahmed wrote: > > [...] > > > diff --git a/mm/vmscan.c b/mm/vmscan.c > > index c82bd89f90364..049e39202e6ce 100644 > > --- a/mm/vmscan.c > > +++ b/mm/vmscan.c > > @@ -188,18 +188,6 @@ struct scan_control { > > */ > > int vm_swappiness = 60; > > > > -static void set_task_reclaim_state(struct task_struct *task, > > - struct reclaim_state *rs) > > -{ > > - /* Check for an overwrite */ > > - WARN_ON_ONCE(rs && task->reclaim_state); > > - > > - /* Check for the nulling of an already-nulled member */ > > - WARN_ON_ONCE(!rs && !task->reclaim_state); > > - > > - task->reclaim_state = rs; > > -} > > - > > LIST_HEAD(shrinker_list); > > DECLARE_RWSEM(shrinker_rwsem); > > > > @@ -511,6 +499,59 @@ static bool writeback_throttling_sane(struct scan_control *sc) > > } > > #endif > > > > +static void set_task_reclaim_state(struct task_struct *task, > > + struct reclaim_state *rs) > > +{ > > + /* Check for an overwrite */ > > + WARN_ON_ONCE(rs && task->reclaim_state); > > + > > + /* Check for the nulling of an already-nulled member */ > > + WARN_ON_ONCE(!rs && !task->reclaim_state); > > + > > + task->reclaim_state = rs; > > +} > > Nit: I just think such movement not necessary while it loses the "git > blame" information easily. > > Instead of moving this here without major benefit, why not just define > flush_reclaim_state() right after previous set_task_reclaim_state()? An earlier version did that, but we would have to add a forward declaration of global_reclaim() (or cgroup_reclaim()), as they are defined after the previous position of set_task_reclaim_state(). > > > + > > +/* > > + * flush_reclaim_state(): add pages reclaimed outside of LRU-based reclaim to > > + * scan_control->nr_reclaimed. > > + */ > > +static void flush_reclaim_state(struct scan_control *sc, > > + struct reclaim_state *rs) > > +{ > > + /* > > + * Currently, reclaim_state->reclaimed includes three types of pages > > + * freed outside of vmscan: > > + * (1) Slab pages. > > + * (2) Clean file pages from pruned inodes. > > + * (3) XFS freed buffer pages. > > + * > > + * For all of these cases, we have no way of finding out whether these > > + * pages were related to the memcg under reclaim. For example, a freed > > + * slab page could have had only a single object charged to the memcg > > + * under reclaim. Also, populated inodes are not on shrinker LRUs > > + * anymore except on highmem systems. > > + * > > + * Instead of over-reporting the reclaimed pages in a memcg reclaim, > > + * only count such pages in global reclaim. This prevents unnecessary > > + * retries during memcg charging and false positive from proactive > > + * reclaim (memory.reclaim). > > + * > > + * For uncommon cases were the freed pages were actually significantly > > + * charged to the memcg under reclaim, and we end up under-reporting, it > > + * should be fine. The freed pages will be uncharged anyway, even if > > + * they are not reported properly, and we will be able to make forward > > + * progress in charging (which is usually in a retry loop). > > + * > > + * We can go one step further, and report the uncharged objcg pages in > > + * memcg reclaim, to make reporting more accurate and reduce > > + * under-reporting, but it's probably not worth the complexity for now. > > + */ > > + if (rs && global_reclaim(sc)) { > > + sc->nr_reclaimed += rs->reclaimed; > > + rs->reclaimed = 0; > > + } > > +} > > + > > static long xchg_nr_deferred(struct shrinker *shrinker, > > struct shrink_control *sc) > > { > > @@ -5346,10 +5387,7 @@ static int shrink_one(struct lruvec *lruvec, struct scan_control *sc) > > vmpressure(sc->gfp_mask, memcg, false, sc->nr_scanned - scanned, > > sc->nr_reclaimed - reclaimed); > > > > - if (global_reclaim(sc)) { > > - sc->nr_reclaimed += current->reclaim_state->reclaimed_slab; > > - current->reclaim_state->reclaimed_slab = 0; > > - } > > + flush_reclaim_state(sc, current->reclaim_state); > > > > return success ? MEMCG_LRU_YOUNG : 0; > > } > > @@ -6474,10 +6512,7 @@ static void shrink_node(pg_data_t *pgdat, struct scan_control *sc) > > > > shrink_node_memcgs(pgdat, sc); > > > > - if (reclaim_state && global_reclaim(sc)) { > > - sc->nr_reclaimed += reclaim_state->reclaimed_slab; > > - reclaim_state->reclaimed_slab = 0; > > - } > > + flush_reclaim_state(sc, reclaim_state); > > IIUC reclaim_state here still points to current->reclaim_state. Could it > change at all? > > Is it cleaner to make flush_reclaim_state() taking "sc" only if it always > references current->reclaim_state? Good point. I think it's always current->reclaim_state. I think we can make flush_reclaim_state() only take "sc" as an argument, and remove the "reclaim_state" local variable in shrink_node() completely. > > > > > /* Record the subtree's reclaim efficiency */ > > if (!sc->proactive) > > -- > > 2.40.0.348.gf938b09366-goog > > > > -- > Peter Xu >
diff --git a/fs/inode.c b/fs/inode.c index 4558dc2f13557..e60fcc41faf17 100644 --- a/fs/inode.c +++ b/fs/inode.c @@ -864,8 +864,7 @@ static enum lru_status inode_lru_isolate(struct list_head *item, __count_vm_events(KSWAPD_INODESTEAL, reap); else __count_vm_events(PGINODESTEAL, reap); - if (current->reclaim_state) - current->reclaim_state->reclaimed_slab += reap; + mm_account_reclaimed_pages(reap); } iput(inode); spin_lock(lru_lock); diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c index 54c774af6e1c6..15d1e5a7c2d34 100644 --- a/fs/xfs/xfs_buf.c +++ b/fs/xfs/xfs_buf.c @@ -286,8 +286,7 @@ xfs_buf_free_pages( if (bp->b_pages[i]) __free_page(bp->b_pages[i]); } - if (current->reclaim_state) - current->reclaim_state->reclaimed_slab += bp->b_page_count; + mm_account_reclaimed_pages(bp->b_page_count); if (bp->b_pages != bp->b_page_array) kmem_free(bp->b_pages); diff --git a/include/linux/swap.h b/include/linux/swap.h index 209a425739a9f..e131ac155fb95 100644 --- a/include/linux/swap.h +++ b/include/linux/swap.h @@ -153,13 +153,28 @@ union swap_header { * memory reclaim */ struct reclaim_state { - unsigned long reclaimed_slab; + /* pages reclaimed outside of LRU-based reclaim */ + unsigned long reclaimed; #ifdef CONFIG_LRU_GEN /* per-thread mm walk data */ struct lru_gen_mm_walk *mm_walk; #endif }; +/* + * mm_account_reclaimed_pages(): account reclaimed pages outside of LRU-based + * reclaim + * @pages: number of pages reclaimed + * + * If the current process is undergoing a reclaim operation, increment the + * number of reclaimed pages by @pages. + */ +static inline void mm_account_reclaimed_pages(unsigned long pages) +{ + if (current->reclaim_state) + current->reclaim_state->reclaimed += pages; +} + #ifdef __KERNEL__ struct address_space; diff --git a/mm/slab.c b/mm/slab.c index dabc2a671fc6f..64bf1de817b24 100644 --- a/mm/slab.c +++ b/mm/slab.c @@ -1392,8 +1392,7 @@ static void kmem_freepages(struct kmem_cache *cachep, struct slab *slab) smp_wmb(); __folio_clear_slab(folio); - if (current->reclaim_state) - current->reclaim_state->reclaimed_slab += 1 << order; + mm_account_reclaimed_pages(1 << order); unaccount_slab(slab, order, cachep); __free_pages(&folio->page, order); } diff --git a/mm/slob.c b/mm/slob.c index fe567fcfa3a39..79cc8680c973c 100644 --- a/mm/slob.c +++ b/mm/slob.c @@ -61,7 +61,7 @@ #include <linux/slab.h> #include <linux/mm.h> -#include <linux/swap.h> /* struct reclaim_state */ +#include <linux/swap.h> /* mm_account_reclaimed_pages() */ #include <linux/cache.h> #include <linux/init.h> #include <linux/export.h> @@ -211,9 +211,7 @@ static void slob_free_pages(void *b, int order) { struct page *sp = virt_to_page(b); - if (current->reclaim_state) - current->reclaim_state->reclaimed_slab += 1 << order; - + mm_account_reclaimed_pages(1 << order); mod_node_page_state(page_pgdat(sp), NR_SLAB_UNRECLAIMABLE_B, -(PAGE_SIZE << order)); __free_pages(sp, order); diff --git a/mm/slub.c b/mm/slub.c index 39327e98fce34..7aa30eef82350 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -11,7 +11,7 @@ */ #include <linux/mm.h> -#include <linux/swap.h> /* struct reclaim_state */ +#include <linux/swap.h> /* mm_account_reclaimed_pages() */ #include <linux/module.h> #include <linux/bit_spinlock.h> #include <linux/interrupt.h> @@ -2063,8 +2063,7 @@ static void __free_slab(struct kmem_cache *s, struct slab *slab) /* Make the mapping reset visible before clearing the flag */ smp_wmb(); __folio_clear_slab(folio); - if (current->reclaim_state) - current->reclaim_state->reclaimed_slab += pages; + mm_account_reclaimed_pages(pages); unaccount_slab(slab, order, s); __free_pages(&folio->page, order); } diff --git a/mm/vmscan.c b/mm/vmscan.c index c82bd89f90364..049e39202e6ce 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -188,18 +188,6 @@ struct scan_control { */ int vm_swappiness = 60; -static void set_task_reclaim_state(struct task_struct *task, - struct reclaim_state *rs) -{ - /* Check for an overwrite */ - WARN_ON_ONCE(rs && task->reclaim_state); - - /* Check for the nulling of an already-nulled member */ - WARN_ON_ONCE(!rs && !task->reclaim_state); - - task->reclaim_state = rs; -} - LIST_HEAD(shrinker_list); DECLARE_RWSEM(shrinker_rwsem); @@ -511,6 +499,59 @@ static bool writeback_throttling_sane(struct scan_control *sc) } #endif +static void set_task_reclaim_state(struct task_struct *task, + struct reclaim_state *rs) +{ + /* Check for an overwrite */ + WARN_ON_ONCE(rs && task->reclaim_state); + + /* Check for the nulling of an already-nulled member */ + WARN_ON_ONCE(!rs && !task->reclaim_state); + + task->reclaim_state = rs; +} + +/* + * flush_reclaim_state(): add pages reclaimed outside of LRU-based reclaim to + * scan_control->nr_reclaimed. + */ +static void flush_reclaim_state(struct scan_control *sc, + struct reclaim_state *rs) +{ + /* + * Currently, reclaim_state->reclaimed includes three types of pages + * freed outside of vmscan: + * (1) Slab pages. + * (2) Clean file pages from pruned inodes. + * (3) XFS freed buffer pages. + * + * For all of these cases, we have no way of finding out whether these + * pages were related to the memcg under reclaim. For example, a freed + * slab page could have had only a single object charged to the memcg + * under reclaim. Also, populated inodes are not on shrinker LRUs + * anymore except on highmem systems. + * + * Instead of over-reporting the reclaimed pages in a memcg reclaim, + * only count such pages in global reclaim. This prevents unnecessary + * retries during memcg charging and false positive from proactive + * reclaim (memory.reclaim). + * + * For uncommon cases were the freed pages were actually significantly + * charged to the memcg under reclaim, and we end up under-reporting, it + * should be fine. The freed pages will be uncharged anyway, even if + * they are not reported properly, and we will be able to make forward + * progress in charging (which is usually in a retry loop). + * + * We can go one step further, and report the uncharged objcg pages in + * memcg reclaim, to make reporting more accurate and reduce + * under-reporting, but it's probably not worth the complexity for now. + */ + if (rs && global_reclaim(sc)) { + sc->nr_reclaimed += rs->reclaimed; + rs->reclaimed = 0; + } +} + static long xchg_nr_deferred(struct shrinker *shrinker, struct shrink_control *sc) { @@ -5346,10 +5387,7 @@ static int shrink_one(struct lruvec *lruvec, struct scan_control *sc) vmpressure(sc->gfp_mask, memcg, false, sc->nr_scanned - scanned, sc->nr_reclaimed - reclaimed); - if (global_reclaim(sc)) { - sc->nr_reclaimed += current->reclaim_state->reclaimed_slab; - current->reclaim_state->reclaimed_slab = 0; - } + flush_reclaim_state(sc, current->reclaim_state); return success ? MEMCG_LRU_YOUNG : 0; } @@ -6474,10 +6512,7 @@ static void shrink_node(pg_data_t *pgdat, struct scan_control *sc) shrink_node_memcgs(pgdat, sc); - if (reclaim_state && global_reclaim(sc)) { - sc->nr_reclaimed += reclaim_state->reclaimed_slab; - reclaim_state->reclaimed_slab = 0; - } + flush_reclaim_state(sc, reclaim_state); /* Record the subtree's reclaim efficiency */ if (!sc->proactive)
During reclaim, we keep track of pages reclaimed from other means than LRU-based reclaim through scan_control->reclaim_state->reclaimed_slab, which we stash a pointer to in current task_struct. However, we keep track of more than just reclaimed slab pages through this. We also use it for clean file pages dropped through pruned inodes, and xfs buffer pages freed. Rename reclaimed_slab to reclaimed, and add a helper function that wraps updating it through current, so that future changes to this logic are contained within mm/vmscan.c. Additionally, add a flush_reclaim_state() helper to wrap using reclaim_state->reclaimed to updated sc->nr_reclaimed, and use that helper to add an elaborate comment about why we only do the update for global reclaim. Finally, move set_task_reclaim_state() next to flush_reclaim_state() so that all reclaim_state helpers are in close proximity for easier readability. Signed-off-by: Yosry Ahmed <yosryahmed@google.com> --- fs/inode.c | 3 +- fs/xfs/xfs_buf.c | 3 +- include/linux/swap.h | 17 +++++++++- mm/slab.c | 3 +- mm/slob.c | 6 ++-- mm/slub.c | 5 ++- mm/vmscan.c | 75 ++++++++++++++++++++++++++++++++------------ 7 files changed, 78 insertions(+), 34 deletions(-)