Only minimum file operations for refresh_ms file is implemented.
Further implement its designed behavior, the periodic essential files
content update,  using repeat mode damon_call().

If non-zero value is written to the file, update DAMON sysfs files for
auto-tuned monitoring intervals, DAMOS stats, and auto-tuned DAMOS quota
values, which are essential to be monitored in most DAMON use cases.
The user-written non-zero value becomes the time delay between the
update.  If zero is written to the file, the periodic refresh is
disabled.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 mm/damon/sysfs.c | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/mm/damon/sysfs.c b/mm/damon/sysfs.c
index 4296dc201f4d..6d2b0dab50cb 100644
--- a/mm/damon/sysfs.c
+++ b/mm/damon/sysfs.c
@@ -1509,6 +1509,32 @@ static struct damon_ctx *damon_sysfs_build_ctx(
 	return ctx;
 }
 
+static int damon_sysfs_repeat_call_fn(void *data)
+{
+	struct damon_sysfs_kdamond *sysfs_kdamond = data;
+	static unsigned long next_update_jiffies;
+
+	if (!sysfs_kdamond->refresh_ms)
+		return 0;
+	if (time_before(jiffies, next_update_jiffies))
+		return 0;
+	next_update_jiffies = jiffies +
+		msecs_to_jiffies(sysfs_kdamond->refresh_ms);
+
+	if (!mutex_trylock(&damon_sysfs_lock))
+		return 0;
+	damon_sysfs_upd_tuned_intervals(sysfs_kdamond);
+	damon_sysfs_upd_schemes_stats(sysfs_kdamond);
+	damon_sysfs_upd_schemes_effective_quotas(sysfs_kdamond);
+	mutex_unlock(&damon_sysfs_lock);
+	return 0;
+}
+
+static struct damon_call_control damon_sysfs_repeat_call_control = {
+	.fn = damon_sysfs_repeat_call_fn,
+	.repeat = true,
+};
+
 static int damon_sysfs_turn_damon_on(struct damon_sysfs_kdamond *kdamond)
 {
 	struct damon_ctx *ctx;
@@ -1533,6 +1559,9 @@ static int damon_sysfs_turn_damon_on(struct damon_sysfs_kdamond *kdamond)
 		return err;
 	}
 	kdamond->damon_ctx = ctx;
+
+	damon_sysfs_repeat_call_control.data = kdamond;
+	damon_call(ctx, &damon_sysfs_repeat_call_control);
 	return err;
 }
 
-- 
2.39.5