[PATCH 4/4] mm: memcontrol: fix NUMA round-robin reclaim at intermediate level

[Johannes Weiner]

When a cgroup is reclaimed on behalf of a configured limit, reclaim
needs to round-robin through all NUMA nodes that hold pages of the
memcg in question. However, when assembling the mask of candidate NUMA
nodes, the code only consults the *local* cgroup LRU counters, not the
recursive counters for the entire subtree. Cgroup limits are
frequently configured against intermediate cgroups that do not have
memory on their own LRUs. In this case, the node mask will always come
up empty and reclaim falls back to scanning only the current node.

If a cgroup subtree has some memory on one node but the processes are
bound to another node afterwards, the limit reclaim will never age or
reclaim that memory anymore.

To fix this, use the recursive LRU counts for a cgroup subtree to
determine which nodes hold memory of that cgroup.

The code has been broken like this forever, so it doesn't seem to be a
problem in practice. I just noticed it while reviewing the way the LRU
counters are used in general.

Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
---
 mm/memcontrol.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 2eb2d4ef9b34..2535e54e7989 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1512,13 +1512,13 @@ static bool test_mem_cgroup_node_reclaimable(struct mem_cgroup *memcg,
 {
 	struct lruvec *lruvec = mem_cgroup_lruvec(NODE_DATA(nid), memcg);
 
-	if (lruvec_page_state_local(lruvec, NR_INACTIVE_FILE) ||
-	    lruvec_page_state_local(lruvec, NR_ACTIVE_FILE))
+	if (lruvec_page_state(lruvec, NR_INACTIVE_FILE) ||
+	    lruvec_page_state(lruvec, NR_ACTIVE_FILE))
 		return true;
 	if (noswap || !total_swap_pages)
 		return false;
-	if (lruvec_page_state_local(lruvec, NR_INACTIVE_ANON) ||
-	    lruvec_page_state_local(lruvec, NR_ACTIVE_ANON))
+	if (lruvec_page_state(lruvec, NR_INACTIVE_ANON) ||
+	    lruvec_page_state(lruvec, NR_ACTIVE_ANON))
 		return true;
 	return false;
 
-- 
2.21.0