Re: [PATCH v2] mm/damon/core: allow esz to be set to zero

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

On Wed, 02 Sep 2026 08:30:46 +0000 sashiko-bot@kernel.org wrote:

> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [High] The patch breaks purely time-based quotas by unconditionally zeroing the effective size quota (`esz`) for DAMOS schemes without goals.
> --
> 
> commit 34629844ff11daf28855cce5457468ad8bc08c73
> Author: Liew Rui Yan <aethernet65535@gmail.com>
> 
> mm/damon/core: allow esz to be set to zero
> 
> This commit updates damos_set_effective_quota() to allow the effective quota
> to be set to zero when the temporal quota goal tuner achieves its goal.
> Previously, the quota was clamped to min_region_sz, preventing it from
> reaching zero.
> 
> > diff --git a/mm/damon/core.c b/mm/damon/core.c
> > index df22621765911..73dc9a70fb12b 100644
> > --- a/mm/damon/core.c
> > +++ b/mm/damon/core.c
> > @@ -3251,6 +3251,9 @@ static void damos_set_effective_quota(struct damon_ctx *ctx, struct damos *s)
> >  	if (quota->sz && quota->sz < esz)
> >  		esz = quota->sz;
> >  
> > +	if (!quota->esz_bp)
> > +		esz = 0;
> > +
> 
> [Severity: High]
> Could this cause a regression for schemes that use purely time-based quotas?
> 
> If a scheme is configured with a time-based quota (quota->ms > 0) but has no
> quota goals (list_empty(&quota->goals)), quota->esz_bp remains at its default
> initialization value of 0.
> 
> While damos_set_effective_quota() correctly computes esz from the throughput
> and quota->ms, this unconditional check will then force esz to 0 because
> quota->esz_bp is 0. An esz of 0 causes damos_quota_is_full() to always return
> true, effectively breaking schemes relying only on time-based quotas.

Yes, thank you for pointing this out!

esz_bp is a meaningful field only when (!list_empty(&quota->goals)), so
the correct check should be:

'''
if (!list_empty(&quota->goals) && !quota->esz_bp)
    esz = 0;
'''

> 
> >  	quota->esz = esz;
> >  }
> >
> 
> -- 
> Sashiko AI review · https://sashiko.dev/#/patchset/20260902082050.19566-1-aethernet65535@gmail.com?part=1

Best regards,
Rui Yan