Re: [RFC PATCH 4/9] mm/damon/core: use damos_quota_is_set() in damos_adjust_quota()

[Kunwu Chan <kunwu.chan@gmail.com>]

On Sat, 12 Sep 2026 13:08:05 -0700 SJ Park <sj@kernel.org> wrote:

> damos_adjust_quota() is manually checking if the user set the DAMOS
> quota.  There is a dedicated helper, damos_quota_is_set(), for the
> purpose.  Use the helper.
> 
> Signed-off-by: SJ Park <sj@kernel.org>
> ---
>  mm/damon/core.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/damon/core.c b/mm/damon/core.c
> index cf10f6d725c19..dd27068cb83e3 100644
> --- a/mm/damon/core.c
> +++ b/mm/damon/core.c
> @@ -3344,7 +3344,7 @@ static void damos_adjust_quota(struct damon_ctx *c, struct damos *s)
>  	unsigned long cumulated_sz, cached_esz;
>  	unsigned int score, max_score = 0;
>  
> -	if (!quota->ms && !quota->sz && list_empty(&quota->goals))
> +	if (!damos_quota_is_set(quota))

Hi SJ,
This is more than a cleanup, because damos_quota_is_set() also checks
quota->esz, which the original condition did not.

The path that makes this matter: damos_commit_quota() copies ms and sz
from sysfs but not esz.  So if a scheme runs with a non-zero ms, then
the user sets ms=0 and commits, the running scheme gets ms=0 while esz
keeps its old value.

The old check would then return early, leaving esz stale.  That stale
esz is visible to damos_valid_target() and damos_quota_is_full(),
which also use damos_quota_is_set().

With the helper, damos_adjust_quota() proceeds into
damos_set_effective_quota(), where the first branch resets esz from sz
when ms and goals are unset.

The code change is correct, but worth noting the behavioral change in
the commit message.

Thanks,
Kunwu

>  		return;
>  
>  	/* First charge window */
> -- 
> 2.47.3
> 

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