Re: [RFC PATCH v3 1/4] mm/damon/sysfs: set goal_tuner after scheme creation

[SeongJae Park <sj@kernel.org>]

On Mon, 23 Feb 2026 12:32:29 +0000 Ravi Jonnalagadda <ravis.opensrc@gmail.com> wrote:

> damon_new_scheme() always sets quota.goal_tuner to CONSIST (the default)
> regardless of what was passed in the quota struct. This caused the sysfs
> goal_tuner setting to be ignored.
> 
> The comment in damon_new_scheme() says "quota.goals and .goal_tuner
> should be separately set by caller", but the sysfs code wasn't doing
> this. Add explicit assignment of goal_tuner after damon_new_scheme()
> returns to properly apply the user's setting.
> 
> Without this fix, setting goal_tuner to "temporal" via sysfs has no
> effect - the scheme always uses the CONSIST (feed loop) tuner, causing
> overshoot when the goal is reached instead of immediate stop.

Thank you for catching this, Ravi!  So, this is a fix for the RFC patch series
[1] that not yet merged, right?  I think this fix is better to be carried with
the series, and squashed into the broken commit to not introduce unnecessary
regression.

So, if you don't mind, I will squash this into the sysfs-schemes part change on
my tree, with your Co-developed-by: tag.

[1] https://lore.kernel.org/20260212062314.69961-1-sj@kernel.org
[2] https://lore.kernel.org/20260212062314.69961-4-sj@kernel.org

> 
> Signed-off-by: Ravi Jonnalagadda <ravis.opensrc@gmail.com>

Reviewed-by: SeongJae Park <sj@kernel.org>

> ---
>  mm/damon/sysfs-schemes.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/mm/damon/sysfs-schemes.c b/mm/damon/sysfs-schemes.c
> index bbea908074bb..fe2e3b2db9e1 100644
> --- a/mm/damon/sysfs-schemes.c
> +++ b/mm/damon/sysfs-schemes.c
> @@ -2809,6 +2809,9 @@ static struct damos *damon_sysfs_mk_scheme(
>  	if (!scheme)
>  		return NULL;
>  
> +	/* Set goal_tuner after damon_new_scheme() as it defaults to CONSIST */
> +	scheme->quota.goal_tuner = sysfs_quotas->goal_tuner;
> +
>  	err = damos_sysfs_add_quota_score(sysfs_quotas->goals, &scheme->quota);
>  	if (err) {
>  		damon_destroy_scheme(scheme);

To follow the order on the comment ("quota.goals and .goal_tuner should be
separately set by caller"), I'd prefer setting the goal_tuner after
damos_sysfs_add_quota_Score() call here, if you don't mind.  Let me know if you
prefer keeping the current order.  If not, I will just make the change when I
apply this to damon/next.


Thanks,
SJ

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