Re: [PATCH 6.12.y 1/5] 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/core: inaccurate tried stats on split failure in
  damos_apply_scheme()
--

commit 2d3797cf5f053ac8bc0b4587f17ff69eb9813ce6
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
damos_apply_scheme() when splitting a region to fit within the remaining
size 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 81d44e41de210..6ef77741b783b 100644
> --- a/mm/damon/core.c
> +++ b/mm/damon/core.c

[ ... ]

> @@ -1470,7 +1470,8 @@ static void damos_apply_scheme(struct damon_ctx *c, struct damon_target *t,
>  					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;
>  		}
>  		if (damos_filter_out(c, t, r, s))
>  			return;

[Severity: Low]
Does jumping to update_stat when damon_split_region_at() fails
inaccurately inflate s->stat.nr_tried and s->stat.sz_tried?  At this
point sz holds the non-zero remaining quota, so damos_update_stat()
increments s->stat.nr_tried and adds sz to s->stat.sz_tried even though
scheme application and damos_filter_out() were skipped.  Because
quota->charged_sz is not updated on this failure path, any further
matching regions that also fail to split in the same walk will
repeatedly add the remaining quota to s->stat.sz_tried.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261108195145.115792-1-sj@kernel.org?part=1