From 8ec07b0620ac2a1be92a2e565aa7ae95f02a93a5 Mon Sep 17 00:00:00 2001 From: Yu Zhao Date: Thu, 7 Dec 2023 23:14:04 -0700 Subject: [PATCH] mm/mglru: fix underprotected page cache commit 081488051d28d32569ebb7c7a23572778b2e7d57 upstream. Unmapped folios accessed through file descriptors can be underprotected. Those folios are added to the oldest generation based on: 1. The fact that they are less costly to reclaim (no need to walk the rmap and flush the TLB) and have less impact on performance (don't cause major PFs and can be non-blocking if needed again). 2. The observation that they are likely to be single-use. E.g., for client use cases like Android, its apps parse configuration files and store the data in heap (anon); for server use cases like MySQL, it reads from InnoDB files and holds the cached data for tables in buffer pools (anon). However, the oldest generation can be very short lived, and if so, it doesn't provide the PID controller with enough time to respond to a surge of refaults. (Note that the PID controller uses weighted refaults and those from evicted generations only take a half of the whole weight.) In other words, for a short lived generation, the moving average smooths out the spike quickly. To fix the problem: 1. For folios that are already on LRU, if they can be beyond the tracking range of tiers, i.e., five accesses through file descriptors, move them to the second oldest generation to give them more time to age. (Note that tiers are used by the PID controller to statistically determine whether folios accessed multiple times through file descriptors are worth protecting.) 2. When adding unmapped folios to LRU, adjust the placement of them so that they are not too close to the tail. The effect of this is similar to the above. On Android, launching 55 apps sequentially: Before After Change workingset_refault_anon 25641024 25598972 0% workingset_refault_file 115016834 106178438 -8% Link: https://lkml.kernel.org/r/20231208061407.2125867-1-yuzhao@google.com Fixes: ac35a4902374 ("mm: multi-gen LRU: minimal implementation") Signed-off-by: Yu Zhao Reported-by: Charan Teja Kalla Tested-by: Kalesh Singh Cc: T.J. Mercier Cc: Kairui Song Cc: Hillf Danton Cc: Jaroslav Pulchart Cc: Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman --- include/linux/mm_inline.h | 23 ++++++++++++++--------- mm/vmscan.c | 2 +- mm/workingset.c | 6 +++--- 3 files changed, 18 insertions(+), 13 deletions(-) diff --git a/include/linux/mm_inline.h b/include/linux/mm_inline.h index 4ef6c09cc2ee..c21e19a1514d 100644 --- a/include/linux/mm_inline.h +++ b/include/linux/mm_inline.h @@ -231,22 +231,27 @@ static inline bool lru_gen_add_folio(struct lruvec *lruvec, struct folio *folio, if (folio_test_unevictable(folio) || !lrugen->enabled) return false; /* - * There are three common cases for this page: - * 1. If it's hot, e.g., freshly faulted in or previously hot and - * migrated, add it to the youngest generation. - * 2. If it's cold but can't be evicted immediately, i.e., an anon page - * not in swapcache or a dirty page pending writeback, add it to the - * second oldest generation. - * 3. Everything else (clean, cold) is added to the oldest generation. + * There are four common cases for this page: + * 1. If it's hot, i.e., freshly faulted in, add it to the youngest + * generation, and it's protected over the rest below. + * 2. If it can't be evicted immediately, i.e., a dirty page pending + * writeback, add it to the second youngest generation. + * 3. If it should be evicted first, e.g., cold and clean from + * folio_rotate_reclaimable(), add it to the oldest generation. + * 4. Everything else falls between 2 & 3 above and is added to the + * second oldest generation if it's considered inactive, or the + * oldest generation otherwise. See lru_gen_is_active(). */ if (folio_test_active(folio)) seq = lrugen->max_seq; else if ((type == LRU_GEN_ANON && !folio_test_swapcache(folio)) || (folio_test_reclaim(folio) && (folio_test_dirty(folio) || folio_test_writeback(folio)))) - seq = lrugen->min_seq[type] + 1; - else + seq = lrugen->max_seq - 1; + else if (reclaiming || lrugen->min_seq[type] + MIN_NR_GENS >= lrugen->max_seq) seq = lrugen->min_seq[type]; + else + seq = lrugen->min_seq[type] + 1; gen = lru_gen_from_seq(seq); flags = (gen + 1UL) << LRU_GEN_PGOFF; diff --git a/mm/vmscan.c b/mm/vmscan.c index 93d6f27dd40b..3f090faa6377 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -4770,7 +4770,7 @@ static bool sort_folio(struct lruvec *lruvec, struct folio *folio, struct scan_c } /* protected */ - if (tier > tier_idx) { + if (tier > tier_idx || refs == BIT(LRU_REFS_WIDTH)) { int hist = lru_hist_from_seq(lrugen->min_seq[type]); gen = folio_inc_gen(lruvec, folio, false); diff --git a/mm/workingset.c b/mm/workingset.c index ae7e984b23c6..6e4699055ed3 100644 --- a/mm/workingset.c +++ b/mm/workingset.c @@ -289,10 +289,10 @@ static void lru_gen_refault(struct folio *folio, void *shadow) * 1. For pages accessed through page tables, hotter pages pushed out * hot pages which refaulted immediately. * 2. For pages accessed multiple times through file descriptors, - * numbers of accesses might have been out of the range. + * they would have been protected by sort_folio(). */ - if (lru_gen_in_fault() || refs == BIT(LRU_REFS_WIDTH)) { - folio_set_workingset(folio); + if (lru_gen_in_fault() || refs >= BIT(LRU_REFS_WIDTH) - 1) { + set_mask_bits(&folio->flags, 0, LRU_REFS_MASK | BIT(PG_workingset)); mod_lruvec_state(lruvec, WORKINGSET_RESTORE_BASE + type, delta); } unlock: