The patch titled
Subject: Multi-gen LRU: Avoid race in inc_min_seq()
has been added to the -mm mm-unstable branch. Its filename is
mm-unstable-multi-gen-lru-avoid-race-in-inc_min_seq.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-unstable-multi-gen-lru-avoid-race-in-inc_min_seq.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: Kalesh Singh <kaleshsingh@xxxxxxxxxx>
Subject: Multi-gen LRU: Avoid race in inc_min_seq()
Date: Tue, 1 Aug 2023 19:56:03 -0700
inc_max_seq() will try to inc_min_seq() if nr_gens == MAX_NR_GENS. This
is because the generations are reused (the last oldest now empty
generation will become the next youngest generation).
inc_min_seq() is retried until successful, dropping the lru_lock
and yielding the CPU on each failure, and retaking the lock before
trying again:
while (!inc_min_seq(lruvec, type, can_swap)) {
spin_unlock_irq(&lruvec->lru_lock);
cond_resched();
spin_lock_irq(&lruvec->lru_lock);
}
However, the initial condition that required incrementing the min_seq
(nr_gens == MAX_NR_GENS) is not retested. This can change by another
call to inc_max_seq() from run_aging() with force_scan=true from the
debugfs interface.
Since the eviction stalls when the nr_gens == MIN_NR_GENS, avoid
unnecessarily incrementing the min_seq by rechecking the number of
generations before each attempt.
This issue was uncovered in previous discussion on the list by Yu Zhao
and Aneesh Kumar [1].
[1] https://lore.kernel.org/linux-mm/CAOUHufbO7CaVm=xjEb1avDhHVvnC8pJmGyKcFf2iY_dpf+zR3w@xxxxxxxxxxxxxx/
Link: https://lkml.kernel.org/r/20230802025606.346758-2-kaleshsingh@xxxxxxxxxx
Fixes: d6c3af7d8a2b ("mm: multi-gen LRU: debugfs interface")
Signed-off-by: Kalesh Singh <kaleshsingh@xxxxxxxxxx>
Tested-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@xxxxxxxxxxxxx> [mediatek]
Tested-by: Charan Teja Kalla <quic_charante@xxxxxxxxxxx>
Cc: Yu Zhao <yuzhao@xxxxxxxxxx>
Cc: Aneesh Kumar K V <aneesh.kumar@xxxxxxxxxxxxx>
Cc: Barry Song <baohua@xxxxxxxxxx>
Cc: Brian Geffon <bgeffon@xxxxxxxxxx>
Cc: Jan Alexander Steffens (heftig) <heftig@xxxxxxxxxxxxx>
Cc: Lecopzer Chen <lecopzer.chen@xxxxxxxxxxxx>
Cc: Matthias Brugger <matthias.bgg@xxxxxxxxx>
Cc: Oleksandr Natalenko <oleksandr@xxxxxxxxxxxxxx>
Cc: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
Cc: Steven Barrett <steven@xxxxxxxxxxxx>
Cc: Suleiman Souhlal <suleiman@xxxxxxxxxx>
Cc: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/vmscan.c | 13 +++++++------
1 file changed, 7 insertions(+), 6 deletions(-)
--- a/mm/vmscan.c~mm-unstable-multi-gen-lru-avoid-race-in-inc_min_seq
+++ a/mm/vmscan.c
@@ -4439,7 +4439,7 @@ static void inc_max_seq(struct lruvec *l
int prev, next;
int type, zone;
struct lru_gen_folio *lrugen = &lruvec->lrugen;
-
+restart:
spin_lock_irq(&lruvec->lru_lock);
VM_WARN_ON_ONCE(!seq_is_valid(lruvec));
@@ -4450,11 +4450,12 @@ static void inc_max_seq(struct lruvec *l
VM_WARN_ON_ONCE(!force_scan && (type == LRU_GEN_FILE || can_swap));
- while (!inc_min_seq(lruvec, type, can_swap)) {
- spin_unlock_irq(&lruvec->lru_lock);
- cond_resched();
- spin_lock_irq(&lruvec->lru_lock);
- }
+ if (inc_min_seq(lruvec, type, can_swap))
+ continue;
+
+ spin_unlock_irq(&lruvec->lru_lock);
+ cond_resched();
+ goto restart;
}
/*
_
Patches currently in -mm which might be from kaleshsingh@xxxxxxxxxx are
mm-unstable-multi-gen-lru-fix-per-zone-reclaim.patch
mm-unstable-multi-gen-lru-avoid-race-in-inc_min_seq.patch
mm-unstable-multi-gen-lru-fix-can_swap-in-lru_gen_look_around.patch
