Re: [RFC PATCH 6.18.y 2/5] 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.
> 
> [ ... ]
> Cc: David Gow <davidgow@davidgow.net>
> Cc: Quanmin Yan <yanquanmin1@huawei.com>
> Cc: <stable@vger.kernel.org> # 6.9.x
> (cherry picked from commit 29c6084658af41b5b1fefd873d26d441830ced34)
> Signed-off-by: SJ Park <sj@kernel.org>

Sashiko has reviewed this patch and found no issues.

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