[PATCH v4 3/4] mm: treat memory.low value inclusive

[Roman Gushchin]

If memcg's usage is equal to the memory.low value, avoid reclaiming
from this cgroup while there is a surplus of reclaimable memory.

This sounds more logical and also matches memory.high and memory.max
behavior: both are inclusive.

Empty cgroups are not considered protected, so MEMCG_LOW events
are not emitted for empty cgroups, if there is no more reclaimable
memory in the system.

Signed-off-by: Roman Gushchin <guro@xxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Vladimir Davydov <vdavydov.dev@xxxxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: kernel-team@xxxxxx
Cc: linux-mm@xxxxxxxxx
Cc: cgroups@xxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
---
 mm/memcontrol.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 78cf21f2a943..3d039fa1a8f5 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5608,14 +5608,14 @@ struct cgroup_subsys memory_cgrp_subsys = {
 };
 
 /**
- * mem_cgroup_low - check if memory consumption is below the normal range
+ * mem_cgroup_low - check if memory consumption is in the normal range
  * @root: the top ancestor of the sub-tree being checked
  * @memcg: the memory cgroup to check
  *
  * WARNING: This function is not stateless! It can only be used as part
  *          of a top-down tree iteration, not for isolated queries.
  *
- * Returns %true if memory consumption of @memcg is below the normal range.
+ * Returns %true if memory consumption of @memcg is in the normal range.
  *
  * @root is exclusive; it is never low when looked at directly
  *
@@ -5709,7 +5709,7 @@ bool mem_cgroup_low(struct mem_cgroup *root, struct mem_cgroup *memcg)
 	elow = min(elow, parent_elow * low_usage / siblings_low_usage);
 exit:
 	memcg->memory.elow = elow;
-	return usage < elow;
+	return usage && usage <= elow;
 }
 
 /**
-- 
2.14.3