Re: (sashiko review) [RFC PATCH v5.1 01/11] mm/damon/core: handle <min_region_sz remaining quota as empty

SeongJae Park
2026-04-11T17:56:01Z

TL; DR: no blocker of this patch from sashiko review.

Forwarding full sashiko review in a reply format with my
inline comments below, for sharing details of my view and
doing followup discussions via mails if needed.

> # review url: https://sashiko.dev/#/patchset/20260411164908.77189-2-sj@kernel.org
> # start of sashiko.dev inline review
> commit 2f0a2c02b528b6c75ac3074d06b729bc93bd8589
> Author: SeongJae Park <sj@kernel.org>
>
> mm/damon/core: handle <min_region_sz remaining quota as empty
>
> This commit updates DAMON quota handling to treat a remaining quota of
> less than min_region_sz as effectively fully charged. This ensures that
> charge_target_from and charge_addr_from of the quota are updated properly,
> avoiding applying DAMOS actions too frequently to specific memory areas.
>
> > diff --git a/mm/damon/core.c b/mm/damon/core.c
> > index 12544c60531d3..8dbc365bb8e97 100644
> > --- a/mm/damon/core.c
> > +++ b/mm/damon/core.c
> [ ... ]
> > @@ -2127,8 +2140,7 @@ static void damon_do_apply_schemes(struct damon_ctx *c,
> > continue;
> >
> > /* Check the quota */
> > - if (damos_quota_is_set(quota) &&
> > - quota->charged_sz >= quota->esz)
> > + if (damos_quota_is_full(quota, c->min_region_sz))
> > continue;
>
> With this change, damon_do_apply_schemes() ensures that we only proceed
> to call damos_apply_scheme() when the remaining quota is at least
> c->min_region_sz.
>
> Does this make the if (!sz) check inside damos_apply_scheme() unreachable?
>
> mm/damon/core.c:damos_apply_scheme() {
> ...
> if (c->ops.apply_scheme) {
> if (damos_quota_is_set(quota) &&
> quota->charged_sz + sz > quota->esz) {
> sz = ALIGN_DOWN(quota->esz - quota->charged_sz,
> c->min_region_sz);
> if (!sz)
> goto update_stat;
> ...
> }
>
> Since the remaining quota (quota->esz - quota->charged_sz) is guaranteed to
> be >= c->min_region_sz when reaching this point, ALIGN_DOWN will always
> result in sz >= c->min_region_sz.
>
> Could this check and the goto be removed to clean up the dead code?

Same question was asked on the previous version of this patch. My answer is
also same. This makes sense but better to be done as a separate cleanup work.

>
>
> # end of sashiko.dev inline review
> # review url: https://sashiko.dev/#/patchset/20260411164908.77189-2-sj@kernel.org

Thanks,
SJ

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