mm: memcontrol: replace mem_cgroup_lruvec_online with mem_cgroup_online

mem_cgroup_lruvec_online() takes lruvec, but it only needs memcg.  Since
get_scan_count(), which is the only user of this function, now possesses
pointer to memcg, let's pass memcg directly to mem_cgroup_online() instead
of picking it out of lruvec and rename the function accordingly.

Signed-off-by: Vladimir Davydov <vdavydov@virtuozzo.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.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 014ff89..9a8556e 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1997,7 +1997,7 @@
 	if (current_is_kswapd()) {
 		if (!zone_reclaimable(zone))
 			force_scan = true;
-		if (!mem_cgroup_lruvec_online(lruvec))
+		if (!mem_cgroup_online(memcg))
 			force_scan = true;
 	}
 	if (!global_reclaim(sc))