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 2d978b28a410b25df1acde351630dee387efbbe5..7f63a9381f71ebbb0c1f9bdda94a913c930280f0 100644 (file)
--- 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;