Re: [RFC PATCH 6.12.y 1/5] mm/damon/core: skip applying scheme if region split for quota fails

[SJ Park <sj@kernel.org>]

On Sat, 07 Nov 2026 21:52:35 +0000 sashiko-bot@kernel.org wrote:

> 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 fe019f891ca813eff979dfc83e95ba297bc45135
> Author: SJ Park <sj@kernel.org>
> 
> mm/damon/core: skip applying scheme if region split for quota fails
> 
> This commit changes 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 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]
> Should this return instead of jumping to update_stat when
> damon_split_region_at() fails?
> 
> At this point sz holds the non-zero aligned remaining quota, and
> update_stat calls damos_update_stat(s, sz, sz_applied), which increments
> s->stat.nr_tried and adds sz to s->stat.sz_tried even though scheme
> application and filter evaluation were skipped.  Because quota->charged_sz
> is not updated on this error path, persistent allocation failures across
> subsequent regions larger than the remaining quota will repeatedly add the
> remaining quota sz to s->stat.sz_tried and increment s->stat.nr_tried.

No blocker.  The user impact is minor and  constrained.  Also same issue exists
in the mainline.  If we want to fix this, we should work on the mainline first.

> 
> -- 
> Sashiko AI review · https://sashiko.dev/#/patchset/20261107214525.304638-1-sj@kernel.org?part=1
> 


Thanks,
SJ