The patch titled
Subject: mm/mglru: reset page lru tier bits when activating
has been added to the -mm mm-unstable branch. Its filename is
mm-mglru-reset-page-lru-tier-bits-when-activating.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-mglru-reset-page-lru-tier-bits-when-activating.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Wei Xu <weixugc@xxxxxxxxxx>
Subject: mm/mglru: reset page lru tier bits when activating
Date: Thu, 17 Oct 2024 18:15:28 +0000
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@xxxxxxxxxx
Fixes: 018ee47f1489 ("mm: multi-gen LRU: exploit locality in rmap")
Signed-off-by: Wei Xu <weixugc@xxxxxxxxxx>
Cc: Axel Rasmussen <axelrasmussen@xxxxxxxxxx>
Cc: Brian Geffon <bgeffon@xxxxxxxxxx>
Cc: Jan Alexander Steffens <heftig@xxxxxxxxxxxxx>
Cc: Suleiman Souhlal <suleiman@xxxxxxxxxx>
Cc: Yu Zhao <yuzhao@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/mm_inline.h | 15 ++++++++++++++-
include/linux/mmzone.h | 2 ++
mm/vmscan.c | 8 ++++----
3 files changed, 20 insertions(+), 5 deletions(-)
--- a/include/linux/mm_inline.h~mm-mglru-reset-page-lru-tier-bits-when-activating
+++ a/include/linux/mm_inline.h
@@ -155,6 +155,11 @@ static inline int folio_lru_refs(struct
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(str
{
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(str
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() */
--- a/include/linux/mmzone.h~mm-mglru-reset-page-lru-tier-bits-when-activating
+++ a/include/linux/mmzone.h
@@ -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)
--- a/mm/vmscan.c~mm-mglru-reset-page-lru-tier-bits-when-activating
+++ a/mm/vmscan.c
@@ -2602,8 +2602,6 @@ 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)
@@ -4138,8 +4136,10 @@ void lru_gen_look_around(struct page_vma
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();
@@ -4370,7 +4370,7 @@ static bool isolate_folio(struct lruvec
/* 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);
_
Patches currently in -mm which might be from weixugc@xxxxxxxxxx are
mm-mglru-reset-page-lru-tier-bits-when-activating.patch
