mm: memcontrol: replace node summing with memcg_page_state()

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

Link: http://lkml.kernel.org/r/20190228163020.24100-4-hannes@cmpxchg.orgSigned-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>

mm/memcontrol.c

@@ -746,10 +746,13 @@ static unsigned long mem_cgroup_nr_lru_pages(struct mem_cgroup *memcg,
 			unsigned int lru_mask)
 {
 	unsigned long nr = 0;
-	int nid;
+	enum lru_list lru;
 
-	for_each_node_state(nid, N_MEMORY)
-		nr += mem_cgroup_node_nr_lru_pages(memcg, nid, lru_mask);
+	for_each_lru(lru) {
+		if (!(BIT(lru) & lru_mask))
+			continue;
+		nr += memcg_page_state(memcg, NR_LRU_BASE + lru);
+	}
 	return nr;
 }