On Thu 04-03-21 09:35:08, Tim Chen wrote:

On 2/18/21 11:13 AM, Michal Hocko wrote:

quoted

Fixes: 4e41695356fb ("memory controller: soft limit reclaim on contention")
Acked-by: Michal Hocko <mhocko-IBi9RG/b67k@public.gmane.org>

Thanks!

quoted

---
 mm/memcontrol.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index ed5cc78a8dbf..a51bf90732cb 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c

@@ -3505,8 +3505,12 @@ unsigned long mem_cgroup_soft_limit_reclaim(pg_data_t *pgdat, int order,
 			loop > MEM_CGROUP_MAX_SOFT_LIMIT_RECLAIM_LOOPS))
 			break;
 	} while (!nr_reclaimed);
-	if (next_mz)
+	if (next_mz) {
+		spin_lock_irq(&mctz->lock);
+		__mem_cgroup_insert_exceeded(next_mz, mctz, excess);
+		spin_unlock_irq(&mctz->lock);
 		css_put(&next_mz->memcg->css);
+	}
 	return nr_reclaimed;
 }
 

-- 
2.20.1

Mel,

Reviewing this patch a bit more, I realize that there is a chance that the removed
next_mz could be inserted back to the tree from a memcg_check_events
that happen in between.  So we need to make sure that the next_mz
is indeed off the tree and update the excess value before adding it
back.  Update the patch to the patch below.

This scenario is certainly possible but it shouldn't really matter much
as __mem_cgroup_insert_exceeded bails out when the node is on the tree
already.
-- 
Michal Hocko
SUSE Labs