linux-kernel - [PATCH v2] mm/damon/core: skip needless update of damon_attrs in damon_commit

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Message-ID: <20250806234254.10572-1-bijan311@gmail.com>
Date: Wed,  6 Aug 2025 18:42:54 -0500
From: Bijan Tabatabai <bijan311@...il.com>
To: damon@...ts.linux.dev,
	linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Cc: sj@...nel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Bijan Tabatabai <bijantabatab@...ron.com>,
	Bijan Tabatabai <bijan311@...il.com>
Subject: [PATCH v2] mm/damon/core: skip needless update of damon_attrs in damon_commit_ctx()

From: Bijan Tabatabai <bijantabatab@...ron.com>

Currently, damon_commit_ctx() always calls damon_set_attrs() even if the
attributes have not been changed. This can be problematic when the DAMON
state is committed relatively frequently because damon_set_attrs() resets
ctx->next_{aggregation,ops_update}_sis, causing aggregation and ops
update operations to be needlessly delayed.

This patch avoids this by only calling damon_set_attrs() in
damon_commit_ctx when the attributes have been changed.

Cc: Bijan Tabatabai <bijan311@...il.com>
Signed-off-by: Bijan Tabatabai <bijantabatab@...ron.com>
---
Changes from v1[1]:
  - Compare entirety of struct damon_attrs
  - Apply logic in damon_commit_ctx() instead of damon_set_attrs()

[1] https://lore.kernel.org/all/20250806164316.5728-1-bijan311@gmail.com/
---
 mm/damon/core.c | 26 +++++++++++++++++++++++---
 1 file changed, 23 insertions(+), 3 deletions(-)

diff --git a/mm/damon/core.c b/mm/damon/core.c
index 6a2fe1f2c952..80aaeb876bf2 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -570,6 +570,24 @@ void damon_destroy_ctx(struct damon_ctx *ctx)
 	kfree(ctx);
 }
 
+static bool damon_attrs_equals(const struct damon_attrs *attrs1,
+		const struct damon_attrs *attrs2)
+{
+	const struct damon_intervals_goal *ig1 = &attrs1->intervals_goal;
+	const struct damon_intervals_goal *ig2 = &attrs2->intervals_goal;
+
+	return attrs1->sample_interval == attrs2->sample_interval &&
+		attrs1->aggr_interval == attrs2->aggr_interval &&
+		attrs1->ops_update_interval == attrs2->ops_update_interval &&
+		attrs1->min_nr_regions == attrs2->min_nr_regions &&
+		attrs1->max_nr_regions == attrs2->max_nr_regions &&
+		ig1->access_bp == ig2->access_bp &&
+		ig1->aggrs == ig2->aggrs &&
+		ig1->min_sample_us == ig2->min_sample_us &&
+		ig1->max_sample_us == ig2->max_sample_us;
+
+}
+
 static unsigned int damon_age_for_new_attrs(unsigned int age,
 		struct damon_attrs *old_attrs, struct damon_attrs *new_attrs)
 {
@@ -1198,9 +1216,11 @@ int damon_commit_ctx(struct damon_ctx *dst, struct damon_ctx *src)
 	 * 2. ops update should be done after pid handling is done (target
 	 *    committing require putting pids).
 	 */
-	err = damon_set_attrs(dst, &src->attrs);
-	if (err)
-		return err;
+	if (!damon_attrs_equals(&dst->attrs, &src->attrs)) {
+		err = damon_set_attrs(dst, &src->attrs);
+		if (err)
+			return err;
+	}
 	dst->ops = src->ops;
 
 	return 0;
-- 
2.43.0