Re: [RFC PATCH v1.3 04/18] mm/damon/core: handle unreset nr_accesses in damon_nr_accesses_mvsum()

[SeongJae Park <sj@kernel.org>]

On Mon, 22 Jun 2026 14:42:11 +0000 sashiko-bot@kernel.org wrote:

> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [Medium] damon_nr_accesses_mvsum() incorrectly returns stale access data from two aggregation intervals ago during the aggregation reset gap.
> --
> 
> commit 079525184ff6b3e5e3e7c3387647af444428cb84
> Author: SeongJae Park <sj@kernel.org>
> 
> mm/damon/core: handle unreset nr_accesses in damon_nr_accesses_mvsum()
> 
> This commit addresses an issue in damon_nr_accesses_mvsum() where unreset
> nr_accesses can unnecessarily inflate the pseudo moving sum. It adds a check
> to return last_nr_accesses directly if the remaining window is full.
> 
> > diff --git a/mm/damon/core.c b/mm/damon/core.c
> > index bc40a6d10f277..8a7351b4a27c2 100644
> > --- a/mm/damon/core.c
> > +++ b/mm/damon/core.c
> > @@ -268,6 +268,9 @@ unsigned int damon_nr_accesses_mvsum(struct damon_region *r,
> >  			ctx->passed_sample_intervals;
> >  	left_window_bp = mult_frac(left_window, 10000, window_len);
> >  
> > +	if (left_window_bp = 10000)
> > +		return r->last_nr_accesses;
> > +
> 
> [Severity: Medium]
> Will this regression return stale access data from two aggregation intervals
> ago?
> 
> If damon_set_attrs() is executed at the end of an aggregation window, it
> advances ctx->next_aggregation_sis but intentionally does not reset
> r->nr_accesses.
> 
> During this unreset gap, r->nr_accesses correctly retains the fully-aggregated
> data of the just-finished window, while r->last_nr_accesses holds the value
> from two windows ago.
> 
> Because next_aggregation_sis was advanced, left_window_bp evaluates to 10000
> in damon_nr_accesses_mvsum(). Does the new check fall back to the
> stale last_nr_accesses, skipping the most recent interval's data?

Too minor issue.  I will keep this as is, and work on further improvement as I
also mentioned on the commit message.  No blocker for this patch.


Thanks,
SJ

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