Re: [PATCH v7 04/16] mm/mglru: lift the forced protection of reclaimer

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential
issue to consider:
- [Low] mm/mglru: run_eviction() evicts up to max_seq due to sc.priority
  == 0
--

commit cd86952996e1243807567af19d65b021c3573888
Author: Kairui Song <kasong@tencent.com>

mm/mglru: lift the forced protection of reclaimer

This commit drops the MIN_NR_GENS early return in scan_folios() and
extends the raised-priority scan bound up to max_seq so reclaim can
proceed when aging cannot keep up with pressure.

Link: https://github.com/ryncsn/emm-test-project/tree/master/file-anon-mix-pressure [1]
Link: https://lore.kernel.org/linux-mm/20260428-mglru-reclaim-v7-0-02fabb92dc43@tencent.com/ [2]
Link: https://lore.kernel.org/linux-mm/20260502-mglru-fg-v1-0-913619b014d9@tencent.com/ [3]

> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 20199232dd70c..51c2ee66b3ee8 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c

[ ... ]

> @@ -4771,18 +4782,24 @@ static int scan_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
>  	if (sc->priority == DEF_PRIORITY)
>  		min_seq = lrugen->min_seq[type];
>  	else
> -		min_seq = lruvec_populated_min_seq(lruvec, type, lrugen->max_seq - MIN_NR_GENS + 1);
> -
> -	if (get_nr_gens(lruvec, type) == MIN_NR_GENS)
> -		return 0;
> +		min_seq = lruvec_populated_min_seq(lruvec, type, lrugen->max_seq);

[Severity: Low]
Can debugfs proactive eviction via lru_gen_seq_write() -> run_eviction()
now scan and evict folios up to lrugen->max_seq instead of stopping at
the requested target seq?

lru_gen_seq_write() leaves sc.priority zero-initialized (0 !=
DEF_PRIORITY), and run_eviction() loops while seq >=
evictable_min_seq(min_seq, swappiness).  When one evictable type has no
folios in generations <= seq while the other still has min_seq <= seq,
scan_folios() takes the sc->priority != DEF_PRIORITY branch and evicts
folios from newer generations up to max_seq, where sort_folio() also
bypasses tier and reference protection when min_gen == max_gen.

The commit message of later commit "mm/mglru: balance anon and file scan
budget by refault rate" in this series notes setting .priority =
DEF_PRIORITY for the debugfs scan_control, but that initialization is
missing from the code.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261111232603.9934-1-baohua@kernel.org?part=4