[PATCH] mm/damon: Fix the timer always stays active

[PATCH] mm/damon: Fix the timer always stays active

[Hailong Tu]

The timer stays active even if the reclaim mechanism is never enabled,
it is unnecessary overhead can be completely avoided by using module_param_call() for enabled flag.
---
 mm/damon/reclaim.c | 24 ++++++++++++++++++++++--
 1 file changed, 22 insertions(+), 2 deletions(-)

diff --git a/mm/damon/reclaim.c b/mm/damon/reclaim.c
index e34c4d0c4d93..389c4be4f62b 100644
--- a/mm/damon/reclaim.c
+++ b/mm/damon/reclaim.c
@@ -28,7 +28,6 @@
  * this.
  */
 static bool enabled __read_mostly;
-module_param(enabled, bool, 0600);
 
 /*
  * Time threshold for cold memory regions identification in microseconds.
@@ -358,11 +357,32 @@ static void damon_reclaim_timer_fn(struct work_struct *work)
 			enabled = last_enabled;
 	}
 
-	schedule_delayed_work(&damon_reclaim_timer,
+	if (enabled)
+		schedule_delayed_work(&damon_reclaim_timer,
 			msecs_to_jiffies(ENABLE_CHECK_INTERVAL_MS));
 }
 static DECLARE_DELAYED_WORK(damon_reclaim_timer, damon_reclaim_timer_fn);
 
+static int enabled_show(char *buffer, const struct kernel_param *kp)
+{
+	return sprintf(buffer, "%c\n", enabled ? 'Y' : 'N');
+}
+
+static int enabled_store(const char *val,
+		const struct kernel_param *kp)
+{
+	int rc = param_set_bool(val, kp);
+
+	if (rc < 0)
+		return rc;
+
+	if (enabled)
+		schedule_delayed_work(&damon_reclaim_timer, 0);
+
+	return 0;
+}
+module_param_call(enabled, enabled_store, enabled_show, &enabled, 0600);
+
 static int damon_reclaim_after_aggregation(struct damon_ctx *c)
 {
 	struct damos *s;
-- 
2.25.1

Re: [PATCH] mm/damon: Fix the timer always stays active

[Matthew Wilcox]

On Thu, Apr 21, 2022 at 02:00:31AM +0800, Hailong Tu wrote:
> +static int enabled_show(char *buffer, const struct kernel_param *kp)
> +{
> +	return sprintf(buffer, "%c\n", enabled ? 'Y' : 'N');
> +}

Why duplicate param_get_bool()?