mm-damon-core-fix-unconditionally-skip-last-region.patch removed from -mm tree

The quilt patch titled
Subject: mm/damon/core: fix unconditionally skip last region
has been removed from the -mm tree. Its filename was
mm-damon-core-fix-unconditionally-skip-last-region.patch

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

------------------------------------------------------
From: Liew Rui Yan <[email protected]>
Subject: mm/damon/core: fix unconditionally skip last region
Date: Tue, 8 Sep 2026 06:47:38 -0700

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.

---

 mm/damon/core.c |   25 ++++++++++++++-----------
 1 file changed, 14 insertions(+), 11 deletions(-)

@@ -2342,36 +2342,39 @@ static bool damos_skip_charged_region(st
 {
 	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,

_

Patches currently in -mm which might be from [email protected] are

docs-mm-damon-design-accurate-semantics-of-nr_snapshots.patch docs-mm-damon-design-difference-between-watermarks-and-nr_snapshots.patch docs-mm-damon-design-fix-typo-of-max_nr_snapshots.patch docs-mm-damon-design-clarify-when-qt_exceeds-increases.patch docs-mm-damon-design-fix-typos-in-temporal-auto-tuning-algorithm-section.patch