Re: [PATCH 6.1.y v3 1/2] mm/damon/core: do non-safe region walk on kdamond_apply_schemes()

[SJ Park <sj@kernel.org>]

On Sat, 10 Oct 2026 06:41:56 +0000 sashiko-bot@kernel.org wrote:

> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [High] mm/damon: double-application of earlier schemes to newly split regions
> --
> 
> commit 01d768c4d318527360ef5913771d20f22a99984a
> Author: SeongJae Park <sj@kernel.org>
> 
> mm/damon/core: do non-safe region walk on kdamond_apply_schemes()
> 
> kdamond_apply_schemes() is using damon_for_each_region_safe(), which is
> safe for deallocation of the region inside the loop. However, the loop
> internal logic does not deallocate regions. Hence it is only wasting the
> next pointer.
> 
> Link: https://lkml.kernel.org/r/20260227170623.95384-3-sj@kernel.org
> 
> > diff --git a/mm/damon/core.c b/mm/damon/core.c
> > index 7afbc20833ea4..b5c85e6488596 100644
> > --- a/mm/damon/core.c
> > +++ b/mm/damon/core.c
> 
> [ ... ]
> 
> > @@ -912,7 +911,7 @@ static void kdamond_apply_schemes(struct damon_ctx *c)
> >  	}
> >  
> >  	damon_for_each_target(t, c) {
> > -		damon_for_each_region_safe(r, next_r, t)
> > +		damon_for_each_region(r, t)
> >  			damon_do_apply_schemes(c, t, r);
> 
> [Severity: High]
> Does this code cause earlier schemes to be applied twice to newly split
> regions?
> 
> If multiple schemes are configured, an earlier scheme (e.g. Scheme 0) might
> apply its action to a full, un-split region. If a later scheme (e.g.
> Scheme 1) then decides to split the region, damon_split_region_at() inserts
> the newly split part into the list immediately after the current region.
> 
> Because this loop in kdamond_apply_schemes() now uses
> damon_for_each_region() instead of the safe variant, the outer loop will
> advance to this newly split region and call damon_do_apply_schemes() on it
> again.
> 
> Will this cause damon_do_apply_schemes() to evaluate the new region from
> the beginning of the scheme list, resulting in Scheme 0 executing its
> memory management actions (like madvise) and counting statistics a second
> time on the same memory range?

The same issue exists in the mainline.  The user impact is minor.  No blocker
of this patch in my opinion.  I will separately work on it.

> 
> >  	}
> >  }
> 
> -- 
> Sashiko AI review · https://sashiko.dev/#/patchset/20261010063042.8611-1-sj@kernel.org?part=1


Thanks,
SJ