Re: [PATCH 6.18.y] mm/damon/core: disallow time-quota setting zero esz

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] The newly added `ctx` parameter in `damos_set_effective_quota()` is unused, and the function incorrectly uses the `DAMON_MIN_REGION` macro instead of `ctx->min_sz_region`.
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commit 8afd735e4c663dcbcca090e71f37ad10c37c705a
Author: SeongJae Park <sj@kernel.org>

mm/damon/core: disallow time-quota setting zero esz

When DAMOS scheme throughput is very slow, the time quota can make the
effective size quota smaller than the context's minimum region size, causing
actions to be skipped. This commit attempts to fix the problem by ensuring
the effective size quota is at least the minimum region size.

Link: https://lore.kernel.org/20260407003153.79589-1-sj@kernel.org
Link: https://lore.kernel.org/20260405192504.110014-1-sj@kernel.org [1]

> diff --git a/mm/damon/core.c b/mm/damon/core.c
> --- a/mm/damon/core.c
> +++ b/mm/damon/core.c
> @@ -2124,7 +2124,8 @@ static unsigned long damos_quota_score(struct damos_quota *quota)
>  /*
>   * Called only if quota->ms, or quota->sz are set, or quota->goals is not empty
>   */
> -static void damos_set_effective_quota(struct damos_quota *quota)
> +static void damos_set_effective_quota(struct damos_quota *quota,
> +		struct damon_ctx *ctx)
>  {
>  	unsigned long throughput;
>  	unsigned long esz = ULONG_MAX;

[ ... ]

> @@ -2150,6 +2151,7 @@ static void damos_set_effective_quota(struct damos_quota *quota)
>  		else
>  			throughput = PAGE_SIZE * 1024;
>  		esz = min(throughput * quota->ms, esz);
> +		esz = max(DAMON_MIN_REGION, esz);

Should this be using ctx->min_sz_region instead of DAMON_MIN_REGION?

The commit message mentions bounding the effective size quota to
damon_ctx->min_region_sz, and the ctx parameter was successfully added
to the function signature. 

However, the ctx parameter is left unused here and the macro is used as a
hardcoded bound instead. Since ctx->min_sz_region can be dynamically
configured, can the effective size quota still fall below it with this
implementation?

>  	}
>  
>  	if (quota->sz && quota->sz < esz)

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Sashiko AI review · https://sashiko.dev/#/patchset/20260504130127.25364-1-sj@kernel.org?part=1