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 ca194864d8028b835e425f32a03e156f1fe9c2a6..9965a77d53e5bf06c1a2140c3002da9cf634fa69 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)