mm-damon-core-process-damon_call_control-requests-on-a-local-list.patch removed from -mm tree

merged mm-stable Andrew Morton 1 participant 1 message Jan 31

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Andrew Morton

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2026-01-31 22:25 UTC #0 lore raw

The quilt patch titled
Subject: mm/damon/core: process damon_call_control requests on a local list
has been removed from the -mm tree. Its filename was
mm-damon-core-process-damon_call_control-requests-on-a-local-list.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: SeongJae Park <[email protected]>
Subject: mm/damon/core: process damon_call_control requests on a local list
Date: Sat, 17 Jan 2026 09:52:51 -0800

kdamond_call() handles damon_call() requests on the ->call_controls list of damon_ctx, which is shared with damon_call() callers. To protect the list from concurrent accesses while letting the callback function independent of the call_controls_lock, the function does complicated locking operations. For each damon_call_control object on the list, the function removes the control object from the list under locking, invoke the callback of the control object without locking, and then puts the control object back to the list if needed, under locking. It is complicated, and can contend the locks more frequently with other DAMON API caller threads as the number of concurrent callback requests increases. Contention overhead is not a big deal, but the increased race opportunity can make headaches.

Simplify the locking sequence by moving all damon_call_control objects from the shared list to a local list at once under the single lock protection, processing the callback requests without locking, and adding back repeat mode controls to the shared list again at once again, again under the single lock protection. This change makes the number of locking in kdamond_call() be always two, regardless of the number of the queued requests.

Link https://lkml.kernel.org/r/[email protected] open here

Signed-off-by SeongJae Park <[email protected]>

Signed-off-by Andrew Morton <[email protected]>

---

 mm/damon/core.c |   59 ++++++++++++++++------------------------------
 1 file changed, 21 insertions(+), 38 deletions(-)

mm/damon/core.c renamed from mm/damon/core.c~mm-damon-core-process-damon_call_control-requests-on-a-local-list +21 ~~-38~~

@@ -2649,48 +2649,31 @@ static void kdamond_usleep(unsigned long
  */
 static void kdamond_call(struct damon_ctx *ctx, bool cancel)
 {
-	struct damon_call_control *control;
-	LIST_HEAD(repeat_controls);
-	int ret = 0;
-
-	while (true) {
-		mutex_lock(&ctx->call_controls_lock);
-		control = list_first_entry_or_null(&ctx->call_controls,
-				struct damon_call_control, list);
-		mutex_unlock(&ctx->call_controls_lock);
-		if (!control)
-			break;
-		if (cancel) {
+	struct damon_call_control *control, *next;
+	LIST_HEAD(controls);
+
+	mutex_lock(&ctx->call_controls_lock);
+	list_splice_tail_init(&ctx->call_controls, &controls);
+	mutex_unlock(&ctx->call_controls_lock);
+
+	list_for_each_entry_safe(control, next, &controls, list) {
+		if (!control->repeat || cancel)
+			list_del(&control->list);
+
+		if (cancel)
 			control->canceled = true;
-		} else {
-			ret = control->fn(control->data);
-			control->return_code = ret;
-		}
-		mutex_lock(&ctx->call_controls_lock);
-		list_del(&control->list);
-		mutex_unlock(&ctx->call_controls_lock);
-		if (!control->repeat) {
+		else
+			control->return_code = control->fn(control->data);
+
+		if (!control->repeat)
 			complete(&control->completion);
-		} else if (control->canceled && control->dealloc_on_cancel) {
+		else if (control->canceled && control->dealloc_on_cancel)
 			kfree(control);
-			continue;
-		} else {
-			list_add(&control->list, &repeat_controls);
-		}
-	}
-	while (true) {
-		control = list_first_entry_or_null(&repeat_controls,
-				struct damon_call_control, list);
-		if (!control)
-			break;
-		/* Unlink from the repeate_controls list. */
-		list_del(&control->list);
-		if (cancel)
-			continue;
-		mutex_lock(&ctx->call_controls_lock);
-		list_add(&control->list, &ctx->call_controls);
-		mutex_unlock(&ctx->call_controls_lock);
 	}
+
+	mutex_lock(&ctx->call_controls_lock);
+	list_splice_tail(&controls, &ctx->call_controls);
+	mutex_unlock(&ctx->call_controls_lock);
 }
 
 /* Returns negative error code if it's not activated but should return */

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