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mm/mglru: reset page lru tier bits when activating

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When a folio is activated, lru_gen_add_folio() moves the folio to the
youngest generation.  But unlike folio_update_gen()/folio_inc_gen(),
lru_gen_add_folio() doesn't reset the folio lru tier bits (LRU_REFS_MASK |
LRU_REFS_FLAGS).  This inconsistency can affect how pages are aged via
folio_mark_accessed() (e.g.  fd accesses), though no user visible impact
related to this has been detected yet.

Note that lru_gen_add_folio() cannot clear PG_workingset if the activation
is due to workingset refault, otherwise PSI accounting will be skipped. 
So fix lru_gen_add_folio() to clear the lru tier bits other than
PG_workingset when activating a folio, and also clear all the lru tier
bits when a folio is activated via folio_activate() in
lru_gen_look_around().

Link: https://lkml.kernel.org/r/20241017181528.3358821-1-weixugc@google.com
Fixes: 018ee47f14 ("mm: multi-gen LRU: exploit locality in rmap")
Signed-off-by: Wei Xu <weixugc@google.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Brian Geffon <bgeffon@google.com>
Cc: Jan Alexander Steffens <heftig@archlinux.org>
Cc: Suleiman Souhlal <suleiman@google.com>
Cc: Yu Zhao <yuzhao@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Wei Xu 2024-10-17 18:15:28 +00:00 committed by Andrew Morton
parent d3ea85c6c5
commit f1001f3d3b
3 changed files with 20 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

15
include/linux/mm_inline.h
View File

@ -155,6 +155,11 @@ static inline int folio_lru_refs(struct folio *folio)
return ((flags & LRU_REFS_MASK) >> LRU_REFS_PGOFF) + workingset;
}
static inline void folio_clear_lru_refs(struct folio *folio)
{
set_mask_bits(&folio->flags, LRU_REFS_MASK | LRU_REFS_FLAGS, 0);
}
static inline int folio_lru_gen(struct folio *folio)
{
unsigned long flags = READ_ONCE(folio->flags);
@ -222,6 +227,7 @@ static inline bool lru_gen_add_folio(struct lruvec *lruvec, struct folio *folio,
{
unsigned long seq;
unsigned long flags;
unsigned long mask;
int gen = folio_lru_gen(folio);
int type = folio_is_file_lru(folio);
int zone = folio_zonenum(folio);
@ -257,7 +263,14 @@ static inline bool lru_gen_add_folio(struct lruvec *lruvec, struct folio *folio,
gen = lru_gen_from_seq(seq);
flags = (gen + 1UL) << LRU_GEN_PGOFF;
/* see the comment on MIN_NR_GENS about PG_active */
set_mask_bits(&folio->flags, LRU_GEN_MASK | BIT(PG_active), flags);
mask = LRU_GEN_MASK;
/*
* Don't clear PG_workingset here because it can affect PSI accounting
* if the activation is due to workingset refault.
*/
if (folio_test_active(folio))
mask |= LRU_REFS_MASK | BIT(PG_referenced) | BIT(PG_active);
set_mask_bits(&folio->flags, mask, flags);
lru_gen_update_size(lruvec, folio, -1, gen);
/* for folio_rotate_reclaimable() */

2
include/linux/mmzone.h
View File

@ -403,6 +403,8 @@ enum {
NR_LRU_GEN_CAPS
};
#define LRU_REFS_FLAGS (BIT(PG_referenced) | BIT(PG_workingset))
#define MIN_LRU_BATCH BITS_PER_LONG
#define MAX_LRU_BATCH (MIN_LRU_BATCH * 64)

8
mm/vmscan.c
View File

@ -2603,8 +2603,6 @@ static bool should_clear_pmd_young(void)
* shorthand helpers
******************************************************************************/
#define LRU_REFS_FLAGS (BIT(PG_referenced) | BIT(PG_workingset))
#define DEFINE_MAX_SEQ(lruvec) \
unsigned long max_seq = READ_ONCE((lruvec)->lrugen.max_seq)
@ -4142,8 +4140,10 @@ bool lru_gen_look_around(struct page_vma_mapped_walk *pvmw)
old_gen = folio_lru_gen(folio);
if (old_gen < 0)
folio_set_referenced(folio);
else if (old_gen != new_gen)
else if (old_gen != new_gen) {
folio_clear_lru_refs(folio);
folio_activate(folio);
}
}
arch_leave_lazy_mmu_mode();
@ -4376,7 +4376,7 @@ static bool isolate_folio(struct lruvec *lruvec, struct folio *folio, struct sca
/* see the comment on MAX_NR_TIERS */
if (!folio_test_referenced(folio))
set_mask_bits(&folio->flags, LRU_REFS_MASK | LRU_REFS_FLAGS, 0);
folio_clear_lru_refs(folio);
/* for shrink_folio_list() */
folio_clear_reclaim(folio);