From d5028f9f7d8de5c375c52b98976b6f310e73398f Mon Sep 17 00:00:00 2001
From: Vladimir Davydov <vdavydov@parallels.com>
Date: Tue, 22 Sep 2015 14:59:20 -0700
Subject: vmscan: fix sane_reclaim helper for legacy memcg

The sane_reclaim() helper is supposed to return false for memcg reclaim
if the legacy hierarchy is used, because the latter lacks dirty
throttling mechanism, and so it did before it was accidentally broken by
commit 33398cf2f360c ("memcg: export struct mem_cgroup").  Fix it.

Fixes: 33398cf2f360c ("memcg: export struct mem_cgroup")
Signed-off-by: Vladimir Davydov <vdavydov@parallels.com>
Acked-by: Tejun Heo <tj@kernel.org>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 2d978b2..7f63a93 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -175,7 +175,7 @@ static bool sane_reclaim(struct scan_control *sc)
 	if (!memcg)
 		return true;
 #ifdef CONFIG_CGROUP_WRITEBACK
-	if (memcg->css.cgroup)
+	if (cgroup_on_dfl(memcg->css.cgroup))
 		return true;
 #endif
 	return false;
-- 
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