[RFC PATCH 1/2] memcg: fix memory.low

[Greg Thelen <gthelen@google.com>]

When targeting reclaim to a memcg, protect that memcg from reclaim is
memory consumption of any level is below respective memory.low.

Signed-off-by: Greg Thelen <gthelen@google.com>
---
 mm/memcontrol.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 670e99b68aa6..9668f620203a 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5341,8 +5341,8 @@ struct cgroup_subsys memory_cgrp_subsys = {
  * @root: the top ancestor of the sub-tree being checked
  * @memcg: the memory cgroup to check
  *
- * Returns %true if memory consumption of @memcg, and that of all
- * ancestors up to (but not including) @root, is below the normal range.
+ * Returns %true if memory consumption of @memcg, or any of its ancestors
+ * up to (but not including) @root, is below the normal range.
  *
  * @root is exclusive; it is never low when looked at directly and isn't
  * checked when traversing the hierarchy.
@@ -5379,12 +5379,12 @@ bool mem_cgroup_low(struct mem_cgroup *root, struct mem_cgroup *memcg)
 	if (memcg == root)
 		return false;
 
+	/* If any level is under, then protect @memcg from reclaim */
 	for (; memcg != root; memcg = parent_mem_cgroup(memcg)) {
-		if (page_counter_read(&memcg->memory) >= memcg->low)
-			return false;
+		if (page_counter_read(&memcg->memory) <= memcg->low)
+			return true; /* protect from reclaim */
 	}
-
-	return true;
+	return false; /* not protected from reclaim */
 }
 
 /**
-- 
2.17.0.484.g0c8726318c-goog