* + mm-mglru-fix-stale-batch-updates-after-memcg-reparenting.patch added to mm-hotfixes-unstable branch
@ 2026-07-10 0:26 Andrew Morton
0 siblings, 0 replies; 2+ messages in thread
From: Andrew Morton @ 2026-07-10 0:26 UTC (permalink / raw)
To: mm-commits, yuanchu, weixugc, stable, shakeel.butt,
roman.gushchin, peiyang_he, muchun.song, mhocko, ljs, kasong,
harry, hannes, david, baohua, axelrasmussen, zhengqi.arch, akpm
The patch titled
Subject: mm: mglru: fix stale batch updates after memcg reparenting
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
mm-mglru-fix-stale-batch-updates-after-memcg-reparenting.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-mglru-fix-stale-batch-updates-after-memcg-reparenting.patch
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next via various
branches at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there most days
------------------------------------------------------
From: Qi Zheng <zhengqi.arch@bytedance.com>
Subject: mm: mglru: fix stale batch updates after memcg reparenting
Date: Wed, 1 Jul 2026 15:52:51 +0800
The mglru page table walker batches per-generation size deltas in
walk->nr_pages while walking page tables without holding the lruvec lock.
The reset_batch_size() later folds those deltas into walk->lruvec under
the lruvec lock.
The page table walker can run concurrently with the memcg reparenting path
as follows:
CPU0 CPU1
==== ====
walk_mm
--> walk_page_range
--> update_batch_size
--> walk->nr_pages += delta
mem_cgroup_css_offline
--> memcg_reparent_objcgs
--> lock lruvec
lru_gen_reparent_memcg
--> reparent child folios to parent
unlock lruvec
lock lruvec
reset_batch_size
--> child lrugen->nr_pages += delta
This will trigger the following warning in lru_gen_exit_memcg():
VM_WARN_ON_ONCE(memchr_inv(lruvec->lrugen.nr_pages, 0,
sizeof(lruvec->lrugen.nr_pages)));
And the user-visible impact of underestimated nr_pages in MGLRU was
premature OOMs because MGLRU does not try to reclaim memory when nr_pages
reaches zero, but there are still more pages.
To fix it, make reset_batch_size() check CSS_DYING under RCU before
flushing the pending batch. A non-dying memcg keeps the original lruvec
stable against RCU-delayed offlining; a dying memcg redirects the deltas
to the first non-dying ancestor.
Link: https://lore.kernel.org/20260701075251.56413-1-qi.zheng@linux.dev
Fixes: f304652609ea ("mm: vmscan: prepare for reparenting MGLRU folios")
Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
Reported-by: Peiyang He <peiyang_he@smail.nju.edu.cn>
Closes: https://lore.kernel.org/all/5A9E929D82717101+12fcf643-efb8-4b9a-a53a-1e28cc894f0b@smail.nju.edu.cn
Reviewed-by: Harry Yoo (Oracle) <harry@kernel.org>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Barry Song <baohua@kernel.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kairui Song <kasong@tencent.com>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Wei Xu <weixugc@google.com>
Cc: Yuanchu Xie <yuanchu@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
mm/vmscan.c | 41 ++++++++++++++++++++++++++++++++++-------
1 file changed, 34 insertions(+), 7 deletions(-)
--- a/mm/vmscan.c~mm-mglru-fix-stale-batch-updates-after-memcg-reparenting
+++ a/mm/vmscan.c
@@ -3262,10 +3262,40 @@ static void update_batch_size(struct lru
walk->nr_pages[new_gen][type][zone] += delta;
}
+#ifdef CONFIG_MEMCG
+static struct lruvec *lock_batch_lruvec(struct lruvec *lruvec)
+{
+ struct pglist_data *pgdat = lruvec_pgdat(lruvec);
+ struct mem_cgroup *memcg = lruvec_memcg(lruvec);
+
+ rcu_read_lock();
+
+ /*
+ * The memcg can be NULL when the memory controller is disabled.
+ * Otherwise, the caller keeps the memcg owning @lruvec alive.
+ */
+ while (unlikely(memcg && css_is_dying(&memcg->css))) {
+ memcg = parent_mem_cgroup(memcg);
+ lruvec = mem_cgroup_lruvec(memcg, pgdat);
+ }
+
+ spin_lock_irq(&lruvec->lru_lock);
+
+ return lruvec;
+}
+#else
+static struct lruvec *lock_batch_lruvec(struct lruvec *lruvec)
+{
+ lruvec_lock_irq(lruvec);
+
+ return lruvec;
+}
+#endif
+
static void reset_batch_size(struct lru_gen_mm_walk *walk)
{
int gen, type, zone;
- struct lruvec *lruvec = walk->lruvec;
+ struct lruvec *lruvec = lock_batch_lruvec(walk->lruvec);
struct lru_gen_folio *lrugen = &lruvec->lrugen;
walk->batched = 0;
@@ -3285,6 +3315,8 @@ static void reset_batch_size(struct lru_
lru += LRU_ACTIVE;
__update_lru_size(lruvec, lru, zone, delta);
}
+
+ lruvec_unlock_irq(lruvec);
}
static int should_skip_vma(unsigned long start, unsigned long end, struct mm_walk *args)
@@ -3779,11 +3811,8 @@ static void walk_mm(struct mm_struct *mm
mmap_read_unlock(mm);
}
- if (walk->batched) {
- lruvec_lock_irq(lruvec);
+ if (walk->batched)
reset_batch_size(walk);
- lruvec_unlock_irq(lruvec);
- }
cond_resched();
} while (err == -EAGAIN);
@@ -4867,9 +4896,7 @@ retry:
walk = current->reclaim_state->mm_walk;
if (walk && walk->batched) {
walk->lruvec = lruvec;
- lruvec_lock_irq(lruvec);
reset_batch_size(walk);
- lruvec_unlock_irq(lruvec);
}
mod_lruvec_state(lruvec, PGDEMOTE_KSWAPD + reclaimer_offset(sc),
_
Patches currently in -mm which might be from zhengqi.arch@bytedance.com are
mm-mglru-fix-stale-batch-updates-after-memcg-reparenting.patch
^ permalink raw reply [flat|nested] 2+ messages in thread* + mm-mglru-fix-stale-batch-updates-after-memcg-reparenting.patch added to mm-hotfixes-unstable branch
@ 2026-07-10 23:19 Andrew Morton
0 siblings, 0 replies; 2+ messages in thread
From: Andrew Morton @ 2026-07-10 23:19 UTC (permalink / raw)
To: mm-commits, yuanchu, weixugc, stable, shakeel.butt,
roman.gushchin, peiyang_he, muchun.song, mhocko, ljs, kasong,
harry, hannes, david, baohua, axelrasmussen, zhengqi.arch, akpm
The patch titled
Subject: mm: mglru: fix stale batch updates after memcg reparenting
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
mm-mglru-fix-stale-batch-updates-after-memcg-reparenting.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-mglru-fix-stale-batch-updates-after-memcg-reparenting.patch
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next via various
branches at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there most days
------------------------------------------------------
From: Qi Zheng <zhengqi.arch@bytedance.com>
Subject: mm: mglru: fix stale batch updates after memcg reparenting
Date: Fri, 10 Jul 2026 23:43:18 +0800
The mglru page table walker batches per-generation size deltas in
walk->nr_pages while walking page tables without holding the lruvec lock.
The reset_batch_size() later folds those deltas into walk->lruvec under
the lruvec lock.
The page table walker can run concurrently with the memcg reparenting path
as follows:
CPU0 CPU1
==== ====
walk_mm
--> walk_page_range
--> update_batch_size
--> walk->nr_pages += delta
mem_cgroup_css_offline
--> memcg_reparent_objcgs
--> lock lruvec
lru_gen_reparent_memcg
--> reparent child folios to parent
unlock lruvec
lock lruvec
reset_batch_size
--> child lrugen->nr_pages += delta
This will trigger the following warning in lru_gen_exit_memcg():
VM_WARN_ON_ONCE(memchr_inv(lruvec->lrugen.nr_pages, 0,
sizeof(lruvec->lrugen.nr_pages)));
And the user-visible impact of underestimated nr_pages in MGLRU was
premature OOMs because MGLRU does not try to reclaim memory when nr_pages
reaches zero, but there are still more pages.
To fix it, make reset_batch_size() check CSS_DYING under RCU before
flushing the pending batch. A non-dying memcg keeps the original lruvec
stable against RCU-delayed offlining; a dying memcg redirects the deltas
to the first non-dying ancestor.
Link: https://lore.kernel.org/20260710154318.75388-1-qi.zheng@linux.dev
Fixes: f304652609ea ("mm: vmscan: prepare for reparenting MGLRU folios")
Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
Reported-by: Peiyang He <peiyang_he@smail.nju.edu.cn>
Closes: https://lore.kernel.org/all/5A9E929D82717101+12fcf643-efb8-4b9a-a53a-1e28cc894f0b@smail.nju.edu.cn
Reviewed-by: Harry Yoo (Oracle) <harry@kernel.org>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Barry Song <baohua@kernel.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kairui Song <kasong@tencent.com>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Wei Xu <weixugc@google.com>
Cc: Yuanchu Xie <yuanchu@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
include/linux/memcontrol.h | 25 +++++++++++++++++++++++++
mm/vmscan.c | 11 ++++-------
2 files changed, 29 insertions(+), 7 deletions(-)
--- a/include/linux/memcontrol.h~mm-mglru-fix-stale-batch-updates-after-memcg-reparenting
+++ a/include/linux/memcontrol.h
@@ -1472,6 +1472,31 @@ static inline void lruvec_lock_irq(struc
spin_lock_irq(&lruvec->lru_lock);
}
+static inline struct lruvec *lruvec_live_lock_irq(struct lruvec *lruvec)
+{
+#ifdef CONFIG_MEMCG
+ struct pglist_data *pgdat = lruvec_pgdat(lruvec);
+ struct mem_cgroup *memcg = lruvec_memcg(lruvec);
+
+ rcu_read_lock();
+
+ /*
+ * The memcg can be NULL when the memory controller is disabled.
+ * Otherwise, the caller keeps the memcg owning @lruvec alive.
+ */
+ while (unlikely(memcg && css_is_dying(&memcg->css))) {
+ memcg = parent_mem_cgroup(memcg);
+ lruvec = mem_cgroup_lruvec(memcg, pgdat);
+ }
+
+ spin_lock_irq(&lruvec->lru_lock);
+#else
+ lruvec_lock_irq(lruvec);
+#endif
+
+ return lruvec;
+}
+
static inline void lruvec_unlock(struct lruvec *lruvec)
{
spin_unlock(&lruvec->lru_lock);
--- a/mm/vmscan.c~mm-mglru-fix-stale-batch-updates-after-memcg-reparenting
+++ a/mm/vmscan.c
@@ -3265,7 +3265,7 @@ static void update_batch_size(struct lru
static void reset_batch_size(struct lru_gen_mm_walk *walk)
{
int gen, type, zone;
- struct lruvec *lruvec = walk->lruvec;
+ struct lruvec *lruvec = lruvec_live_lock_irq(walk->lruvec);
struct lru_gen_folio *lrugen = &lruvec->lrugen;
walk->batched = 0;
@@ -3285,6 +3285,8 @@ static void reset_batch_size(struct lru_
lru += LRU_ACTIVE;
__update_lru_size(lruvec, lru, zone, delta);
}
+
+ lruvec_unlock_irq(lruvec);
}
static int should_skip_vma(unsigned long start, unsigned long end, struct mm_walk *args)
@@ -3779,11 +3781,8 @@ static void walk_mm(struct mm_struct *mm
mmap_read_unlock(mm);
}
- if (walk->batched) {
- lruvec_lock_irq(lruvec);
+ if (walk->batched)
reset_batch_size(walk);
- lruvec_unlock_irq(lruvec);
- }
cond_resched();
} while (err == -EAGAIN);
@@ -4867,9 +4866,7 @@ retry:
walk = current->reclaim_state->mm_walk;
if (walk && walk->batched) {
walk->lruvec = lruvec;
- lruvec_lock_irq(lruvec);
reset_batch_size(walk);
- lruvec_unlock_irq(lruvec);
}
mod_lruvec_state(lruvec, PGDEMOTE_KSWAPD + reclaimer_offset(sc),
_
Patches currently in -mm which might be from zhengqi.arch@bytedance.com are
mm-mglru-fix-stale-batch-updates-after-memcg-reparenting.patch
^ permalink raw reply [flat|nested] 2+ messages in thread
end of thread, other threads:[~2026-07-10 23:19 UTC | newest]
Thread overview: 2+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2026-07-10 0:26 + mm-mglru-fix-stale-batch-updates-after-memcg-reparenting.patch added to mm-hotfixes-unstable branch Andrew Morton
-- strict thread matches above, loose matches on Subject: below --
2026-07-10 23:19 Andrew Morton
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox