[merged mm-stable] mm-damon-core-skip-aging-from-repeated-aggressive-merging.patch removed from -mm tree

[Andrew Morton <akpm@linux-foundation.org>]

The quilt patch titled
     Subject: mm/damon/core: skip aging from repeated aggressive merging
has been removed from the -mm tree.  Its filename was
     mm-damon-core-skip-aging-from-repeated-aggressive-merging.patch

This patch was dropped because it was merged into the mm-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------
From: SJ Park <sj@kernel.org>
Subject: mm/damon/core: skip aging from repeated aggressive merging
Date: Sun, 12 Jul 2026 09:54:30 -0700

The number of DAMON regions could temporarily exceed the user-defined
maximum number of regions limit for corner cases.  For example, users
could lower the limit via runtime parameters update.  For such a case,
kdamond_merge_regions() repeats merging regions in the case doubling the
merge threshold.  The repeated merge operation could update the age of
regions multiple times.  This corrupts the monitoring results.  Fix the
issue by asking the merge operation to skip aging for the corner case.

The user impact is degradation of the monitoring quality.  The impact
should be mild, since the degradation is only temporal, and it is not
common to happen in realistic setups.

The issue was discovered [1,2] by Sashiko.

Link: https://lore.kernel.org/20260712165432.87609-1-sj@kernel.org
Link: https://lore.kernel.org/20260621203548.10718-1-sj@kernel.org [1]
Link: https://lore.kernel.org/20260709145425.96247-1-sj@kernel.org [2]
Fixes: 310d6c15e910 ("mm/damon/core: merge regions aggressively when max_nr_regions is unmet")
Signed-off-by: SJ Park <sj@kernel.org>
Cc: <stable@vger.kernel.org> # 6.10
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/damon/core.c             |   21 +++++++++++++--------
 mm/damon/tests/core-kunit.h |    2 +-
 2 files changed, 14 insertions(+), 9 deletions(-)

--- a/mm/damon/core.c~mm-damon-core-skip-aging-from-repeated-aggressive-merging
+++ a/mm/damon/core.c
@@ -3308,7 +3308,7 @@ static unsigned int damon_merge_score(st
  * sz_limit	size upper limit of each region
  */
 static void damon_merge_regions_of(struct damon_target *t, unsigned int thres,
-		unsigned long sz_limit, struct damon_ctx *ctx)
+		unsigned long sz_limit, struct damon_ctx *ctx, bool count_age)
 {
 	struct damon_region *r, *prev = NULL, *next;
 	bool use_probe_hits = damon_has_probe_weights(ctx);
@@ -3319,12 +3319,14 @@ static void damon_merge_regions_of(struc
 		score = damon_merge_score(r, false, ctx, use_probe_hits);
 		last_score = damon_merge_score(r, true, ctx, use_probe_hits);
 
-		if (abs_diff(score, last_score) > thres)
-			r->age = 0;
-		else if ((score == 0) != (last_score == 0))
-			r->age = 0;
-		else
-			r->age++;
+		if (count_age) {
+			if (abs_diff(score, last_score) > thres)
+				r->age = 0;
+			else if ((score == 0) != (last_score == 0))
+				r->age = 0;
+			else
+				r->age++;
+		}
 
 		if (!prev)
 			goto set_prev_continue;
@@ -3366,15 +3368,18 @@ static void kdamond_merge_regions(struct
 	struct damon_target *t;
 	unsigned int nr_regions;
 	unsigned int max_thres;
+	bool count_age = true;
 
 	max_thres = c->attrs.aggr_interval /
 		(c->attrs.sample_interval ?  c->attrs.sample_interval : 1);
 	do {
 		nr_regions = 0;
 		damon_for_each_target(t, c) {
-			damon_merge_regions_of(t, threshold, sz_limit, c);
+			damon_merge_regions_of(t, threshold, sz_limit, c,
+					count_age);
 			nr_regions += damon_nr_regions(t);
 		}
+		count_age = false;
 		threshold = max(1, threshold * 2);
 	} while (nr_regions > c->attrs.max_nr_regions &&
 			threshold / 2 < max_thres);
--- a/mm/damon/tests/core-kunit.h~mm-damon-core-skip-aging-from-repeated-aggressive-merging
+++ a/mm/damon/tests/core-kunit.h
@@ -257,7 +257,7 @@ static void damon_test_merge_regions_of(
 		damon_add_region(r, t);
 	}
 
-	damon_merge_regions_of(t, 9, 9999, ctx);
+	damon_merge_regions_of(t, 9, 9999, ctx, true);
 	/* 0-112, 114-130, 130-156, 156-170, 170-230, 230-10170 */
 	KUNIT_EXPECT_EQ(test, damon_nr_regions(t), 6u);
 	for (i = 0; i < 6; i++) {
_

Patches currently in -mm which might be from sj@kernel.org are