Re: [PATCH 04/19] mm/damon/core: ask apply_probe() to return max probe hits weighted sum

[SJ Park <sj@kernel.org>]

On Fri, 10 Jul 2026 14:01:19 +0000 sashiko-bot@kernel.org wrote:

> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [Medium] The apply_probes callback fails to calculate and return the maximum probe hits weighted sum, unconditionally returning 0.
> --
> 
> --- Patch [4]: [PATCH 04/19] mm/damon/core: ask apply_probe() to return max probe hits weighted sum ---
> commit bb862935a31b8d93d0e79b24c1d5bb92b5faf39a
> Author: SJ Park <sj@kernel.org>
> 
> mm/damon/core: ask apply_probe() to return max probe hits weighted sum
> 
> This commit updates the DAMON operations protocol to allow the apply_probes
> callback to calculate and return the maximum probe hits weighted sum. It
> modifies the function signature to take a return_max_wsum parameter and 
> updates the existing implementation in damon_pa_apply_probes() to return 
> an unsigned int.
> 
> > diff --git a/include/linux/damon.h b/include/linux/damon.h
> > index aee28b05acc6c..e7acd8e610a64 100644
> > --- a/include/linux/damon.h
> > +++ b/include/linux/damon.h
> [ ... ]
> > @@ -649,6 +649,8 @@ enum damon_ops_id {
> >   * @apply_probes should apply the data attribute probes to each region and
> >   * accordingly update the probe hits counter of the region.  It should also
> >   * set &damon_region->sampling_addr of each region if ``set_samples`` is true.
> > + * It should also return maximum probe hits weighted sum of regions if
> > + * ``return_max_wsum`` is true.
> >   * @get_scheme_score should return the priority score of a region for a scheme
> >   * as an integer in [0, &DAMOS_MAX_SCORE].
> >   * @apply_scheme is called from @kdamond when a region for user provided
> 
> [ ... ]
> 
> > diff --git a/mm/damon/paddr.c b/mm/damon/paddr.c
> > index ff4fcca949660..3eba3564a31fc 100644
> > --- a/mm/damon/paddr.c
> > +++ b/mm/damon/paddr.c
> [ ... ]
> > @@ -166,7 +166,8 @@ static bool damon_pa_filter_pass(phys_addr_t pa, struct folio *folio,
> >  	return pass;
> >  }
> >  
> > -static void damon_pa_apply_probes(struct damon_ctx *ctx, bool set_samples)
> > +static unsigned int damon_pa_apply_probes(struct damon_ctx *ctx,
> > +		bool set_samples, bool return_max_wsum)
> >  {
> >  	struct damon_target *t;
> >  	struct damon_region *r;
> [ ... ]
> > @@ -194,6 +195,7 @@ static void damon_pa_apply_probes(struct damon_ctx *ctx, bool set_samples)
> >  				folio_put(folio);
> >  		}
> >  	}
> > +	return 0;
> >  }
> 
> [Severity: Medium]
> Will this unconditionally return 0 even when return_max_wsum is true?
> 
> The struct documentation states the callback should return the maximum probe
> hits weighted sum of regions if return_max_wsum is true. However, the
> implementation in damon_pa_apply_probes() simply returns 0 at the end
> without computing the weighted sum.
> 
> Should the maximum weighted sum calculation be implemented here to fulfill
> the updated protocol?

No issue.  No caller sets return_max_wsum true at this moment.

And a later patch in this series will make the argument be respected before
someone sets it true.

> 
> -- 
> Sashiko AI review · https://sashiko.dev/#/patchset/20260710134651.18084-1-sj@kernel.org?part=4


Thanks,
SJ