mm, memcg: bypass high reclaim iteration for cgroup hierarchy root

The root of the hierarchy cannot have high set, so we will never reclaim
based on it.  This makes that clearer and avoids another entry.

Signed-off-by: Chris Down <chris@chrisdown.name>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Roman Gushchin <guro@fb.com>
Cc: Michal Hocko <mhocko@kernel.org>
Link: http://lkml.kernel.org/r/20200312164137.GA1753625@chrisdown.name
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index ca19486..9965a77 100644 (file)
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2254,7 +2254,8 @@ static void reclaim_high(struct mem_cgroup *memcg,
                        continue;
                memcg_memory_event(memcg, MEMCG_HIGH);
                try_to_free_mem_cgroup_pages(memcg, nr_pages, gfp_mask, true);
-       } while ((memcg = parent_mem_cgroup(memcg)));
+       } while ((memcg = parent_mem_cgroup(memcg)) &&
+                !mem_cgroup_is_root(memcg));
 }
 
 static void high_work_func(struct work_struct *work)