[PATCH v2] mm/damon/core: fix false positive in

[Liew Rui Yan <aethernet65535@gmail.com>]

On Wed, 02 Sep 2026 16:18:25 +0800 Liew Rui Yan <aethernet65535@gmail.com> wrote:

> When setting goal_tuner to 'temporal', if the goal is achieved,
> quota->esz_bp will be set to zero.  In this case, damos_quota_is_full()
> will always return true, even if no regions have been tried to apply at
> all.  This causes qt_exceeds to increase unexpectedly.
> 
> Fix it by:
> 
> - Returning false in damos_quota_is_full() when quota->charged_sz is
>   zero.
> - Adding an early exit in damon_do_apply_schemes() for schemes with zero
>   esz.
> 
> Fixes: c7ec7d5f6b3d ("mm/damon/core: handle <min_region_sz remaining quota as empty")
> Cc: <stable@vger.kernel.org> # v7.2.x
> Signed-off-by: Liew Rui Yan <aethernet65535@gmail.com>
> ---
> 
> Changes from v1:
> - v1: https://lore.kernel.org/damon/20260901105925.106186-1-aethernet65535@gmail.com
> - Changed the check in damos_quota_is_full() from '!quota->esz' to
>   '!quota->charged_sz', because the former is an upper bound, while the
>   latter represents the actual quota usage.
> - Added an early exit in damon_do_apply_schemes() to prevent a scheme
>   with zero esz from being evaluated by damos_quota_is_full().
> - Changed patch title, original title: always return false when esz is
>   zero
> 
> ---
>  mm/damon/core.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/mm/damon/core.c b/mm/damon/core.c
> index 8e3ded1a2cf6..de78ad56c8b3 100644
> --- a/mm/damon/core.c
> +++ b/mm/damon/core.c
> @@ -2560,6 +2560,8 @@ static bool damos_quota_is_full(struct damos_quota *quota,
>  {
>  	if (!damos_quota_is_set(quota))
>  		return false;
> +	if (!quota->charged_sz)
> +		return false;
>  	if (quota->charged_sz >= quota->esz)
>  		return true;
>  	/*
> @@ -2666,6 +2668,9 @@ static void damon_do_apply_schemes(struct damon_ctx *c,
>  		if (!s->wmarks.activated)
>  			continue;
>  
> +		if (!quota->esz)
> +			continue;
> +
>  		/* Check the quota */
>  		if (damos_quota_is_full(quota, c->min_region_sz))
>  			continue;
> -- 
> 2.55.0
> 
> 

Please ignore this patch.  The title was truncated, so I've reposted it.
If Sashiko provides a report in this thread that differs from the
reposted version, I'll forward it as well.

Best regards,
Rui Yan