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

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

[Sasha Levin]

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>.

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.

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")
Signed-off-by: Karl Mehltretter <kmehltretter@gmail.com>
Signed-off-by: SJ Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Suggested-by: SJ Park <sj@kernel.org>
Reviewed-by: SJ Park <sj@kernel.org>
Reviewed-by: Kunwu Chan <kunwu.chan@gmail.com>
Assisted-by: LLM
Cc: Lian Wang <lianux.mm@gmail.com>
Cc: <stable@vger.kernel.org> # 6.9.x
---
 mm/damon/core.c | 30 +++++++++++++++++++++++-------
 1 file changed, 23 insertions(+), 7 deletions(-)

diff --git a/mm/damon/core.c b/mm/damon/core.c
index f950a3b9fcb99..71e8cedbc6439 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -2891,6 +2891,28 @@ static inline u64 damos_get_some_mem_psi_total(void)
 
 #endif	/* CONFIG_PSI */
 
+static void damos_set_psi_current_val(u64 now_psi_total,
+		struct damos_quota_goal *goal, struct damos *s)
+{
+	u64 last_psi_total = goal->last_psi_total;
+
+	goal->last_psi_total = now_psi_total;
+	if (last_psi_total != U64_MAX) {
+		goal->current_value = now_psi_total - last_psi_total;
+		return;
+	}
+	/* uninitialized last_psi_total; make no effect this round */
+	if (s->quota.goal_tuner == DAMOS_QUOTA_GOAL_TUNER_CONSIST) {
+		goal->current_value = goal->target_value;
+		return;
+	}
+	/* let temporal tuner show the same achievement as in the last round */
+	if (!s->quota.esz)
+		goal->current_value = goal->target_value;
+	else
+		goal->current_value = 0;
+}
+
 #ifdef CONFIG_NUMA
 static bool invalid_mem_node(int nid)
 {
@@ -3143,13 +3165,7 @@ static void damos_set_quota_goal_current_value(struct damon_ctx *c,
 		break;
 	case DAMOS_QUOTA_SOME_MEM_PSI_US:
 		now_psi_total = damos_get_some_mem_psi_total();
-		/* uninitialized last_psi_total; make no effect this round */
-		if (goal->last_psi_total == U64_MAX)
-			goal->current_value = goal->target_value;
-		else
-			goal->current_value = now_psi_total -
-				goal->last_psi_total;
-		goal->last_psi_total = now_psi_total;
+		damos_set_psi_current_val(now_psi_total, goal, s);
 		break;
 	case DAMOS_QUOTA_NODE_MEM_USED_BP:
 	case DAMOS_QUOTA_NODE_MEM_FREE_BP:
-- 
2.53.0

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]

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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