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authorMinchan Kim <minchan@kernel.org>2022-05-20 00:08:54 +0300
committerakpm <akpm@linux-foundation.org>2022-05-20 00:08:54 +0300
commit6d4675e601357834dadd2ba1d803f6484596015c (patch)
tree4cb1490901fa887fcb0d7ecc34629baa16a4ad18 /include/linux/ksm.h
parentf4840ccfca25db225b3371a8f7b5770febee87c5 (diff)
downloadlinux-6d4675e601357834dadd2ba1d803f6484596015c.tar.xz
mm: don't be stuck to rmap lock on reclaim path
The rmap locks(i_mmap_rwsem and anon_vma->root->rwsem) could be contended under memory pressure if processes keep working on their vmas(e.g., fork, mmap, munmap). It makes reclaim path stuck. In our real workload traces, we see kswapd is waiting the lock for 300ms+(worst case, a sec) and it makes other processes entering direct reclaim, which were also stuck on the lock. This patch makes lru aging path try_lock mode like shink_page_list so the reclaim context will keep working with next lru pages without being stuck. if it found the rmap lock contended, it rotates the page back to head of lru in both active/inactive lrus to make them consistent behavior, which is basic starting point rather than adding more heristic. Since this patch introduces a new "contended" field as out-param along with try_lock in-param in rmap_walk_control, it's not immutable any longer if the try_lock is set so remove const keywords on rmap related functions. Since rmap walking is already expensive operation, I doubt the const would help sizable benefit( And we didn't have it until 5.17). In a heavy app workload in Android, trace shows following statistics. It almost removes rmap lock contention from reclaim path. Martin Liu reported: Before: max_dur(ms) min_dur(ms) max-min(dur)ms avg_dur(ms) sum_dur(ms) count blocked_function 1632 0 1631 151.542173 31672 209 page_lock_anon_vma_read 601 0 601 145.544681 28817 198 rmap_walk_file After: max_dur(ms) min_dur(ms) max-min(dur)ms avg_dur(ms) sum_dur(ms) count blocked_function NaN NaN NaN NaN NaN 0.0 NaN 0 0 0 0.127645 1 12 rmap_walk_file [minchan@kernel.org: add comment, per Matthew] Link: https://lkml.kernel.org/r/YnNqeB5tUf6LZ57b@google.com Link: https://lkml.kernel.org/r/20220510215423.164547-1-minchan@kernel.org Signed-off-by: Minchan Kim <minchan@kernel.org> Acked-by: Johannes Weiner <hannes@cmpxchg.org> Cc: Suren Baghdasaryan <surenb@google.com> Cc: Michal Hocko <mhocko@suse.com> Cc: John Dias <joaodias@google.com> Cc: Tim Murray <timmurray@google.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Vladimir Davydov <vdavydov.dev@gmail.com> Cc: Martin Liu <liumartin@google.com> Cc: Minchan Kim <minchan@kernel.org> Cc: Matthew Wilcox <willy@infradead.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'include/linux/ksm.h')
-rw-r--r--include/linux/ksm.h4
1 files changed, 2 insertions, 2 deletions
diff --git a/include/linux/ksm.h b/include/linux/ksm.h
index 0630e545f4cb..0b4f17418f64 100644
--- a/include/linux/ksm.h
+++ b/include/linux/ksm.h
@@ -51,7 +51,7 @@ static inline void ksm_exit(struct mm_struct *mm)
struct page *ksm_might_need_to_copy(struct page *page,
struct vm_area_struct *vma, unsigned long address);
-void rmap_walk_ksm(struct folio *folio, const struct rmap_walk_control *rwc);
+void rmap_walk_ksm(struct folio *folio, struct rmap_walk_control *rwc);
void folio_migrate_ksm(struct folio *newfolio, struct folio *folio);
#else /* !CONFIG_KSM */
@@ -79,7 +79,7 @@ static inline struct page *ksm_might_need_to_copy(struct page *page,
}
static inline void rmap_walk_ksm(struct folio *folio,
- const struct rmap_walk_control *rwc)
+ struct rmap_walk_control *rwc)
{
}