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* FAILED: patch "[PATCH] mm/damon/core: fix unconditionally skip last region" failed to apply to 6.12-stable tree
@ 2026-09-29  8:27 gregkh
  2026-09-30  2:33 ` [PATCH 6.12.y 1/3] mm/damon/core: fix wasteful CPU calls by skipping non-existent targets Sasha Levin
                   ` (3 more replies)
  0 siblings, 4 replies; 15+ messages in thread
From: gregkh @ 2026-09-29  8:27 UTC (permalink / raw)
  To: aethernet65535, akpm, sj, stable; +Cc: stable


The patch below does not apply to the 6.12-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-6.12.y
git checkout FETCH_HEAD
git cherry-pick -x b3723b596b548c837a766aae3553c14a7b15af2b
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026092948-agency-overhand-3fd1@gregkh' --subject-prefix 'PATCH 6.12.y' 'HEAD^..'

Possible dependencies:



thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From b3723b596b548c837a766aae3553c14a7b15af2b Mon Sep 17 00:00:00 2001
From: Liew Rui Yan <aethernet65535@gmail.com>
Date: Tue, 8 Sep 2026 06:47:38 -0700
Subject: [PATCH] mm/damon/core: fix unconditionally skip last region

Once quota set, the charge_{target,addr}_from unconditionally skips and
resets at the last region of the tracked target, so the last region can be
skipped even when it has not been processed.

Example:

    1. Target has 2 regions: R1 (0-100 bytes) and R2 (100-200 bytes).
    2. Quota is configured to process only 100 bytes per window.
    3. Window 1: Processes R1 (0-100).  Quota is full.  charge_{target,
       addr}_from is saved at (Target, 100).
    4. Window 2: The loop reaches R2.  Because R2 is
       damon_last_region(t), the old code unconditionally returns true,
       skipping R2 entirely and resetting the charge_{target,addr}_from.

    Result: R2 is permanently skipped even though it has never been
    processed.

However, it is important to note that this is a very minor issue.  This is
because it is triggered only when the previous window saved/kept
charge_{target,addr}_from, and in the next window, all regions except the
last region were skipped by damos_skip_charged_region().

Fix this by only resetting the charge_{target,addr}_from when last region
is reached, only skipping when it is applied or cannot split.

Link: https://lore.kernel.org/20260908134739.96919-1-sj@kernel.org
Fixes: 50585192bc2e ("mm/damon/schemes: skip already charged targets and regions")
Signed-off-by: Liew Rui Yan <aethernet65535@gmail.com>
Reviewed-by: SJ Park <sj@kernel.org>
Signed-off-by: SJ Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: <stable@vger.kernel.org> # v5.16.x

diff --git a/mm/damon/core.c b/mm/damon/core.c
index 2b294fb46648..06a253df8d4b 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -2342,36 +2342,39 @@ static bool damos_skip_charged_region(struct damon_target *t,
 {
 	struct damos_quota *quota = &s->quota;
 	unsigned long sz_to_skip;
+	bool skip = false;
 
 	/* Skip previously charged regions */
 	if (quota->charge_target_from) {
 		if (t != quota->charge_target_from)
 			return true;
-		if (r == damon_last_region(t)) {
-			quota->charge_target_from = NULL;
-			quota->charge_addr_from = 0;
-			return true;
-		}
 		if (quota->charge_addr_from &&
-				r->ar.end <= quota->charge_addr_from)
-			return true;
+				r->ar.end <= quota->charge_addr_from) {
+			skip = true;
+			goto out;
+		}
 
 		if (quota->charge_addr_from && r->ar.start <
 				quota->charge_addr_from) {
 			sz_to_skip = ALIGN_DOWN(quota->charge_addr_from -
 					r->ar.start, min_region_sz);
 			if (!sz_to_skip) {
-				if (damon_sz_region(r) <= min_region_sz)
-					return true;
+				if (damon_sz_region(r) <= min_region_sz) {
+					skip = true;
+					goto out;
+				}
 				sz_to_skip = min_region_sz;
 			}
 			damon_split_region_at(t, r, sz_to_skip);
-			return true;
+			skip = true;
 		}
+	}
+out:
+	if (r == damon_last_region(t)) {
 		quota->charge_target_from = NULL;
 		quota->charge_addr_from = 0;
 	}
-	return false;
+	return skip;
 }
 
 static void damos_update_stat(struct damos *s,


^ permalink raw reply related	[flat|nested] 15+ messages in thread
end of thread, other threads:[~2026-10-11 16:48 UTC | newest]

Thread overview: 15+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2026-09-29  8:27 FAILED: patch "[PATCH] mm/damon/core: fix unconditionally skip last region" failed to apply to 6.12-stable tree gregkh
2026-09-30  2:33 ` [PATCH 6.12.y 1/3] mm/damon/core: fix wasteful CPU calls by skipping non-existent targets Sasha Levin
2026-09-30  2:34   ` [PATCH 6.12.y 2/3] mm/damon: rename DAMON_MIN_REGION to DAMON_MIN_REGION_SZ Sasha Levin
2026-09-30  9:24     ` SJ Park
2026-09-30  9:31       ` SJ Park
2026-09-30  2:34   ` [PATCH 6.12.y 3/3] mm/damon/core: fix unconditionally skip last region Sasha Levin
2026-09-30 13:15     ` Greg KH
2026-09-30  9:28 ` [PATCH 6.12.y] " SJ Park
2026-09-30 10:03   ` SJ Park
2026-09-30 10:14 ` [PATCH 6.12.y v2] " SJ Park
2026-10-02 14:19   ` Sasha Levin
2026-10-09 12:36 ` [PATCH 6.12.y v3 0/2] mm/damon/core: fix last region handling of damos_skip_charged_regions() SJ Park
2026-10-09 12:36   ` [PATCH 6.12.y v3 1/2] mm/damon/core: do non-safe region walk on kdamond_apply_schemes() SJ Park
2026-10-09 12:36   ` [PATCH 6.12.y v3 2/2] mm/damon/core: fix unconditionally skip last region SJ Park
2026-10-11 16:48   ` [PATCH 6.12.y v3 0/2] mm/damon/core: fix last region handling of damos_skip_charged_regions() Sasha Levin

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