linux-kernel - [PATCH] mm, memcg: Bypass high reclaim iteration for cgroup hierarchy root

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Message-ID: <20200312164137.GA1753625@chrisdown.name>
Date:   Thu, 12 Mar 2020 16:41:37 +0000
From:   Chris Down <chris@...isdown.name>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Johannes Weiner <hannes@...xchg.org>, Tejun Heo <tj@...nel.org>,
        linux-mm@...ck.org, cgroups@...r.kernel.org,
        linux-kernel@...r.kernel.org, kernel-team@...com
Subject: [PATCH] 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@...isdown.name>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Johannes Weiner <hannes@...xchg.org>
Cc: Tejun Heo <tj@...nel.org>
Cc: linux-mm@...ck.org
Cc: cgroups@...r.kernel.org
Cc: linux-kernel@...r.kernel.org
Cc: kernel-team@...com
---
 mm/memcontrol.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 63bb6a2aab81..ab9d24a657b9 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2232,7 +2232,8 @@ 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)
-- 
2.25.1