Re: [PATCH 6.1.y 1/2] mm/damon/core: skip applying scheme if region split for quota fails

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential
issue to consider:
- [Low] mm/damon: inflated tried stats in damon_do_apply_schemes() on
  split failure
--

commit 3b087258b4341cba87012b7cb96ed676fd164c12
Author: SJ Park <sj@kernel.org>

mm/damon/core: skip applying scheme if region split for quota fails

This commit updates damon_split_region_at() to return an error code on
allocation failure and skips applying the DAMOS scheme in
damon_do_apply_schemes() when splitting a region to fit the quota fails.

Link: https://lore.kernel.org/20260901131850.98037-1-sj@kernel.org
Link: https://lore.kernel.org/20260901131850.98037-2-sj@kernel.org
Link: https://lore.kernel.org/20260718171523.87547-1-sj@kernel.org [1]

> diff --git a/mm/damon/core.c b/mm/damon/core.c
> index f0da5cb2b88a0..9206737d05ae7 100644
> --- a/mm/damon/core.c
> +++ b/mm/damon/core.c

[ ... ]

> @@ -810,7 +810,8 @@ static void damon_do_apply_schemes(struct damon_ctx *c,
>  						DAMON_MIN_REGION);
>  				if (!sz)
>  					goto update_stat;
> -				damon_split_region_at(t, r, sz);
> +				if (damon_split_region_at(t, r, sz))
> +					goto update_stat;
>  			}
>  			ktime_get_coarse_ts64(&begin);
>  			sz_applied = c->ops.apply_scheme(c, t, r, s);

[Severity: Low]
Does jumping to update_stat on damon_split_region_at() failure inflate
s->stat.nr_tried and s->stat.sz_tried?

When damon_split_region_at() fails, sz is the non-zero remaining quota
size, c->ops.apply_scheme() is skipped, and quota->charged_sz is not
advanced:

mm/damon/core.c:damon_do_apply_schemes() {
	...
update_stat:
		s->stat.nr_tried++;
		s->stat.sz_tried += sz;
	...
}

Because quota->charged_sz remains unchanged, subsequent matching regions
can repeatedly add sz to s->stat.sz_tried if allocation continues to fail.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261108202759.117377-1-sj@kernel.org?part=1