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 33398cf2 ("memcg: export struct mem_cgroup").  Fix it.

Fixes: 33398cf2 ("memcg: export struct mem_cgroup")
Signed-off-by: NVladimir Davydov <vdavydov@parallels.com>
Acked-by: NTejun Heo <tj@kernel.org>
Acked-by: NMichal Hocko <mhocko@suse.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>