mm: memcontrol: replace zone summing with lruvec_page_state()

Instead of adding up the zone counters, use lruvec_page_state() to get the
node state directly.  This is a bit cheaper and more stream-lined.

Link: http://lkml.kernel.org/r/20190228163020.24100-3-hannes@cmpxchg.org
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Roman Gushchin <guro@fb.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 81a0d39..f303814 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -737,7 +737,7 @@ unsigned long mem_cgroup_node_nr_lru_pages(struct mem_cgroup *memcg,
 	for_each_lru(lru) {
 		if (!(BIT(lru) & lru_mask))
 			continue;
-		nr += mem_cgroup_get_lru_size(lruvec, lru);
+		nr += lruvec_page_state(lruvec, NR_LRU_BASE + lru);
 	}
 	return nr;
 }