Re: FAILED: patch "[PATCH] mm/damon/core: keep the temporal tuner quota over an unmeasured PSI round" failed to apply to 6.18-stable tree

[SJ Park <sj@kernel.org>]

Hello,


On Sat,  7 Nov 2026 05:08:54 -0500 Sasha Levin <sashal@kernel.org> wrote:

> The patch below does not apply to the 6.18-stable tree.
> If someone wants it applied there, or to any other stable or longterm
> tree, then please email the backport, including the original git commit
> id to <stable@vger.kernel.org>.

TL;DR: the patch is not needed for 6.18.y.  Please ignore this failure.

> 
> To reproduce the conflict and resubmit, you may use the following commands:
> 
> git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.18.y
> git checkout FETCH_HEAD
> git cherry-pick -x df7d9a0f8d916eeea375430ae3360724afecde15
> # <resolve conflicts, build, test, etc.>
> git commit -s
> git send-email --to '<stable@vger.kernel.org>' --in-reply-to '20261107050853-failed-6.18-df7d9a0f8d91@kernel.org' --subject-prefix 'PATCH 6.18.y' 'HEAD^..'
> 
> Thanks,
> Sasha
> 
> ------------------ original commit in Linus's tree ------------------
> 
> >From df7d9a0f8d916eeea375430ae3360724afecde15 Mon Sep 17 00:00:00 2001
> From: Karl Mehltretter <kmehltretter@gmail.com>
> Date: Tue, 22 Sep 2026 22:51:37 -0700
> Subject: [PATCH] mm/damon/core: keep the temporal tuner quota over an
>  unmeasured PSI round
> 
> The patch in mm-unstable of subject "mm/damon/core: handle uninitialized
> damos_quota_goal->last_psi_total" scores a PSI quota goal without a
> previous sample as achieved.  This leaves the consist tuner's input
> unchanged, but the temporal tuner sets its quota to zero for an achieved
> goal.  A running scheme with a nonzero temporal quota therefore loses a
> charge window after a quota-goal commit.

This patch was meant to be squashed into the mm-unstable patch before being
mainlined.  But seems I failed at clearly communicating it to Andrew, and
checking it further.

This fixup is needed for only temporal tuner available kernel.  Temporal tuner
was merged on 7.1.  So, this patch is not needed for 6.18.y.

> 
> Use the effective quota to preserve the temporal tuner's previous
> goal-achievement state during an unmeasured round, as SJ suggested [1].
> Score the goal as achieved when the effective quota is zero and as not
> achieved otherwise.  A new scheme's initially zero quota stays zero, and
> the consist tuner's behavior is unchanged.
> 
> Move the PSI current-value calculation and last_psi_total update into a
> helper that takes the current PSI total.  This lets a unit test cover the
> unmeasured and measured rounds without depending on system memory
> pressure.
> 
> Link: https://lore.kernel.org/20260923055139.2982-1-sj@kernel.org
> Link: https://lore.kernel.org/damon/20260916001311.101024-1-sj@kernel.org/ [1]
> Fixes: 2dbb60f789cb ("mm/damon/core: implement PSI metric DAMOS quota goal")

FWIW, the above Fixes: is the Fixes: of the mm-unstable patch that this patch
was intended to be squashed into.  Hence the above is incorrect.  Correct one
should be below:

Fixes: 29c6084658af ("mm/damon/core: handle uninitialized damos_quota_goal->last_psi_total")
Cc: <stable@vger.kernel.org> # 7.4.x


Thanks,
SJ

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