Re: [RFC PATCH v1.3 2/4] mm/damon/core: handle uninitialized damos_quota_goal->last_psi_total

[sashiko-bot@kernel.org]

> When DAMOS_QUOTA_SOME_MEM_PSI_US metric damos quota goal is set, the PSI
> delta for the feedback loop is calculated using
> damos_quota_goal->last_psi_total.  However, it is initialized only after
> the first feedback loop.  The first iteration of the loop uses the
> uninitialized value.  As a result, the feedback loop can change the
> effective quota in an unexpected way at the first iteration.
> 
> The user impact of the issue is not big, because the issue impacts only
> the first iteration of the feedback loop.  The feedback loop also has an
> internal cap of the quota adjustment.  The wrong adjustment will soon be
> corrected over a few iterations.  For this reason, doing no
> initialization at commit time was intentional.  It is also explicitly
> commented.  That said, nobody likes behaviors that are unexpected or
> difficult to be expected.
> 
> [ ... ]
> [1] https://lore.kernel.org/20260718005316.89585-1-sj@kernel.org
> 
> Fixes: 2dbb60f789cb ("mm/damon/core: implement PSI metric DAMOS quota goal")
> Cc: <stable@vger.kernel.org> # 6.9.x
> Signed-off-by: SJ Park <sj@kernel.org>

Sashiko has reviewed this patch and found no issues. It looks great!

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