Re: [RFC PATCH v1.2 04/19] mm/damon/core: ask apply_probe() to return max probe hits weighted sum

[SJ Park <sj@kernel.org>]

On Thu, 09 Jul 2026 14:16:38 +0000 sashiko-bot@kernel.org wrote:

> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [Medium] The `damon_pa_apply_probes` callback unconditionally returns 0 instead of computing and returning the maximum probe hits weighted sum when `return_max_wsum` is true, violating the updated API contract.
> --
> 
> --- Patch [4]: [RFC PATCH v1.2 04/19] mm/damon/core: ask apply_probe() to return max probe hits weighted sum ---
> commit ed82d24ec75fdb639533062e293614cb1cebe866
> Author: SJ Park <sj@kernel.org>
> 
> mm/damon/core: ask apply_probe() to return max probe hits weighted sum
> 
> This commit updates the apply_probes() callback protocol in the DAMON
> operations to optionally return the maximum probe hits weighted sum. This
> value is intended to help the core layer adjust regions in the future.
> 
> > diff --git a/include/linux/damon.h b/include/linux/damon.h
> > index 3c2a4d673bf62..4e1845ce83870 100644
> > --- a/include/linux/damon.h
> > +++ b/include/linux/damon.h
> > @@ -648,7 +648,9 @@ enum damon_ops_id {
> >   * of its update.  The value will be used for regions adjustment threshold.
> >   * @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 sampling_addr of each region if ``set_samples`` is true.
> > + * &set 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]
> The kernel-doc for apply_probes states it should return the maximum probe hits
> weighted sum if return_max_wsum is true.
> 
> However, damon_pa_apply_probes() unconditionally returns 0 here without
> computing the weighted sum.
> 
> Will this cause the core layer to receive an incorrect threshold of 0 when it
> starts passing return_max_wsum = true in the future?

This is intentional.  The later patch in this series will implement it.

> 
> >  }
> 
> -- 
> Sashiko AI review · https://sashiko.dev/#/patchset/20260709140600.90950-1-sj@kernel.org?part=4


Thanks,
SJ