On Wed, Sep 22, 2021 at 08:16:20PM +0800, Hillf Danton wrote:

On Mon, 20 Sep 2021 09:54:32 +0100 Mel Gorman wrote:

quoted

+static void
+reclaim_throttle(pg_data_t *pgdat, enum vmscan_throttle_state reason,
+							long timeout)
+{
+	wait_queue_head_t *wqh =3D &pgdat->reclaim_wait;
+	unsigned long start =3D jiffies;
+	long ret;
+	DEFINE_WAIT(wait);
+
+	atomic_inc(&pgdat->nr_reclaim_throttled);
+	WRITE_ONCE(pgdat->nr_reclaim_start,
+		 node_page_state(pgdat, NR_THROTTLED_WRITTEN));

Missing wakeup could happen if the current sleeper overwrites 
pgdat->nr_reclaim_start set by the existing sleeper.

	if (1 == atomic_inc_and_return(&pgdat->nr_reclaim_throttled))
		WRITE_ONCE(pgdat->nr_reclaim_start,
				node_page_state(pgdat, NR_THROTTLED_WRITTEN));

Good spot, will fix.

-- 
Mel Gorman
SUSE Labs