Re: [PATCH 6.6.y v3 1/2] mm/damon/core: do non-safe region walk on kdamond_apply_schemes()

[SJ Park <sj@kernel.org>]

On Fri, 09 Oct 2026 14:02:33 +0000 sashiko-bot@kernel.org wrote:

> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [Medium] mm: damon: double processing of split regions by earlier schemes
> --
> 
> commit de615e5101d6a41f308fef487cc464f7d25abb6e
> Author: SeongJae Park <sj@kernel.org>
> 
> mm/damon/core: do non-safe region walk on kdamond_apply_schemes()
> 
> This commit replaces the safe region iterator with damon_for_each_region()
> in kdamond_apply_schemes() to ensure newly split regions are not ignored
> during iteration. It also simplifies damos_skip_charged_region() by
> removing a workaround that updated the region pointer directly.
> 
> 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 fe91b296f4c66..c86cac855b9b0 100644
> > --- a/mm/damon/core.c
> > +++ b/mm/damon/core.c
> 
> [ ... ]
> 
> > @@ -1134,7 +1134,7 @@ static void damos_adjust_quota(struct damon_ctx *c, struct damos *s)
> >  static void kdamond_apply_schemes(struct damon_ctx *c)
> >  {
> >  	struct damon_target *t;
> > -	struct damon_region *r, *next_r;
> > +	struct damon_region *r;
> >  	struct damos *s;
> >  	unsigned long sample_interval = c->attrs.sample_interval ?
> >  		c->attrs.sample_interval : 1;
> > @@ -1156,7 +1156,7 @@ static void kdamond_apply_schemes(struct damon_ctx *c)
> >  		return;
> >  
> >  	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: Medium]
> Will this change cause earlier schemes to re-process newly split regions?
> 
> When damon_do_apply_schemes() evaluates a region, it sequentially iterates
> through all schemes. If an earlier scheme processes the region, it applies
> its action and updates its quota.
> 
> If a later scheme then hits an address filter or quota while evaluating the
> same region, it splits the region, shrinking it and inserting a new remainder
> region immediately after it in the target list.
> 
> Because the outer loop now dynamically fetches the next region via
> damon_for_each_region(), this newly inserted remainder region is evaluated
> in the very next iteration.
> 
> When damon_do_apply_schemes() processes this remainder region, it starts over
> from the first scheme. Won't this cause the earlier scheme to re-evaluate
> and apply its action a second time, potentially artificially double-charging
> its quota and redundantly applying physical memory operations?

Minor impact issue that also exist in the mainline.  Hence no blocker of this
series in my opinion.  I will separately work on the issue.

> 
> >  	}
> >
> 
> -- 
> Sashiko AI review · https://sashiko.dev/#/patchset/20261009134949.11507-1-sj@kernel.org?part=1
> 


Thanks,
SJ