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

[sashiko-bot@kernel.org]

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?

>  }

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