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...

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@google.com 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_...

Link: https://lkml.kernel.org/r/20230802025606.346758-2-kaleshsingh@google.com Fixes: d6c3af7d8a2b ("mm: multi-gen LRU: debugfs interface") Signed-off-by: Kalesh Singh kaleshsingh@google.com Tested-by: AngeloGioacchino Del Regno angelogioacchino.delregno@collabora.com [mediatek] Tested-by: Charan Teja Kalla quic_charante@quicinc.com Cc: Yu Zhao yuzhao@google.com Cc: Aneesh Kumar K V aneesh.kumar@linux.ibm.com Cc: Barry Song baohua@kernel.org Cc: Brian Geffon bgeffon@google.com Cc: Jan Alexander Steffens (heftig) heftig@archlinux.org Cc: Lecopzer Chen lecopzer.chen@mediatek.com Cc: Matthias Brugger matthias.bgg@gmail.com Cc: Oleksandr Natalenko oleksandr@natalenko.name Cc: Qi Zheng zhengqi.arch@bytedance.com Cc: Steven Barrett steven@liquorix.net Cc: Suleiman Souhlal suleiman@google.com Cc: Suren Baghdasaryan surenb@google.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

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@google.com 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