linux-kernel - [RFC PATCH 08/12] mm/damon/sysfs-schemes: implement max_nr

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Message-ID: <20251123184329.85287-9-sj@kernel.org>
Date: Sun, 23 Nov 2025 10:43:22 -0800
From: SeongJae Park <sj@...nel.org>
To: 
Cc: SeongJae Park <sj@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	damon@...ts.linux.dev,
	linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: [RFC PATCH 08/12] mm/damon/sysfs-schemes: implement max_nr_snapshots file

Add a new DAMON sysfs file for setting and getting the newly introduced
per-DAMON-snapshot level DAMOS deactivation control parameter,
max_nr_snapshots.  The file has a name same to the parameter and placed
under the damos stat directory.

Signed-off-by: SeongJae Park <sj@...nel.org>
---
 mm/damon/sysfs-schemes.c | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/mm/damon/sysfs-schemes.c b/mm/damon/sysfs-schemes.c
index 4d25469f957f..bf1b637d4342 100644
--- a/mm/damon/sysfs-schemes.c
+++ b/mm/damon/sysfs-schemes.c
@@ -205,6 +205,7 @@ struct damon_sysfs_stats {
 	unsigned long sz_ops_filter_passed;
 	unsigned long qt_exceeds;
 	unsigned long nr_snapshots;
+	unsigned long max_nr_snapshots;
 };
 
 static struct damon_sysfs_stats *damon_sysfs_stats_alloc(void)
@@ -275,6 +276,28 @@ static ssize_t nr_snapshots_show(struct kobject *kobj,
 	return sysfs_emit(buf, "%lu\n", stats->nr_snapshots);
 }
 
+static ssize_t max_nr_snapshots_show(struct kobject *kobj,
+		struct kobj_attribute *attr, char *buf)
+{
+	struct damon_sysfs_stats *stats = container_of(kobj,
+			struct damon_sysfs_stats, kobj);
+
+	return sysfs_emit(buf, "%lu\n", stats->max_nr_snapshots);
+}
+
+static ssize_t max_nr_snapshots_store(struct kobject *kobj,
+		struct kobj_attribute *attr, const char *buf, size_t count)
+{
+	struct damon_sysfs_stats *stats = container_of(kobj,
+			struct damon_sysfs_stats, kobj);
+	unsigned long max_nr_snapshots, err = kstrtoul(buf, 0, &max_nr_snapshots);
+
+	if (err)
+		return err;
+	stats->max_nr_snapshots = max_nr_snapshots;
+	return count;
+}
+
 static void damon_sysfs_stats_release(struct kobject *kobj)
 {
 	kfree(container_of(kobj, struct damon_sysfs_stats, kobj));
@@ -301,6 +324,9 @@ static struct kobj_attribute damon_sysfs_stats_qt_exceeds_attr =
 static struct kobj_attribute damon_sysfs_stats_nr_snapshots_attr =
 		__ATTR_RO_MODE(nr_snapshots, 0400);
 
+static struct kobj_attribute damon_sysfs_stats_max_nr_snapshots_attr =
+		__ATTR_RW_MODE(max_nr_snapshots, 0600);
+
 static struct attribute *damon_sysfs_stats_attrs[] = {
 	&damon_sysfs_stats_nr_tried_attr.attr,
 	&damon_sysfs_stats_sz_tried_attr.attr,
@@ -309,6 +335,7 @@ static struct attribute *damon_sysfs_stats_attrs[] = {
 	&damon_sysfs_stats_sz_ops_filter_passed_attr.attr,
 	&damon_sysfs_stats_qt_exceeds_attr.attr,
 	&damon_sysfs_stats_nr_snapshots_attr.attr,
+	&damon_sysfs_stats_max_nr_snapshots_attr.attr,
 	NULL,
 };
 ATTRIBUTE_GROUPS(damon_sysfs_stats);
@@ -2731,6 +2758,7 @@ static struct damos *damon_sysfs_mk_scheme(
 		damon_destroy_scheme(scheme);
 		return NULL;
 	}
+	scheme->max_nr_snapshots = sysfs_scheme->stats->max_nr_snapshots;
 	return scheme;
 }
 
-- 
2.47.3