[PATCH] memcg: schedule high reclaim for remote memcgs on high_work

[Shakeel Butt]

If a memcg is over high limit, memory reclaim is scheduled to run on
return-to-userland. However it is assumed that the memcg is the current
process's memcg. With remote memcg charging for kmem or swapping in a
page charged to remote memcg, current process can trigger reclaim on
remote memcg. So, schduling reclaim on return-to-userland for remote
memcgs will ignore the high reclaim altogether. So, punt the high
reclaim of remote memcgs to high_work.

Signed-off-by: Shakeel Butt <shakeelb@xxxxxxxxxx>
---
 mm/memcontrol.c | 20 ++++++++++++--------
 1 file changed, 12 insertions(+), 8 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index e9db1160ccbc..47439c84667a 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2302,19 +2302,23 @@ static int try_charge(struct mem_cgroup *memcg, gfp_t gfp_mask,
 	 * reclaim on returning to userland.  We can perform reclaim here
 	 * if __GFP_RECLAIM but let's always punt for simplicity and so that
 	 * GFP_KERNEL can consistently be used during reclaim.  @memcg is
-	 * not recorded as it most likely matches current's and won't
-	 * change in the meantime.  As high limit is checked again before
-	 * reclaim, the cost of mismatch is negligible.
+	 * not recorded as the return-to-userland high reclaim will only reclaim
+	 * from current's memcg (or its ancestor). For other memcgs we punt them
+	 * to work queue.
 	 */
 	do {
 		if (page_counter_read(&memcg->memory) > memcg->high) {
-			/* Don't bother a random interrupted task */
-			if (in_interrupt()) {
+			/*
+			 * Don't bother a random interrupted task or if the
+			 * memcg is not current's memcg's ancestor.
+			 */
+			if (in_interrupt() ||
+			    !mm_match_cgroup(current->mm, memcg)) {
 				schedule_work(&memcg->high_work);
-				break;
+			} else {
+				current->memcg_nr_pages_over_high += batch;
+				set_notify_resume(current);
 			}
-			current->memcg_nr_pages_over_high += batch;
-			set_notify_resume(current);
 			break;
 		}
 	} while ((memcg = parent_mem_cgroup(memcg)));
-- 
2.20.1.415.g653613c723-goog