[PATCH v3 1/4] memcg: bail out memory.high when memcg is dying

[Jiayuan Chen]

From: Jiayuan Chen <jiayuan.chen@xxxxxxxxxx>

memory.high reclaims synchronously in the writer's context, and the
latency can be very high - especially when reclaim performs swap I/O, or
under thrashing where the loop may not converge for a long time.

While this runs the kernfs active reference on the file is held, so a
concurrent removal of the same cgroup blocks in kernfs_drain() under
cgroup_mutex until it finishes. Reclaiming a dying cgroup is pointless,
as its pages are reparented to the parent anyway.

Mitigate this by bailing out of the reclaim loop once memcg_is_dying().

Cc: Jiayuan Chen <jiayuan.chen@xxxxxxxxx>
Reported-by: Zhou Yingfu <yingfu.zhou@xxxxxxxxxx>
Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
Signed-off-by: Jiayuan Chen <jiayuan.chen@xxxxxxxxxx>
---
 mm/memcontrol.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index d20ffc827306..4519dc9eae33 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -4794,6 +4794,10 @@ static ssize_t memory_high_write(struct kernfs_open_file *of,
 		if (signal_pending(current))
 			break;
 
+		/* cgroup_rmdir() waits for us with cgroup_mutex held. */
+		if (memcg_is_dying(memcg))
+			break;
+
 		if (!drained) {
 			drain_all_stock(memcg);
 			drained = true;
-- 
2.43.0