mm: memcontrol: clean up memory.events counting function

We only ever count single events, drop the @nr parameter.  Rename the
function accordingly.  Remove low-information kerneldoc.

Link: http://lkml.kernel.org/r/20170404220148.28338-1-hannes@cmpxchg.org
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Vladimir Davydov <vdavydov.dev@gmail.com>
Acked-by: Michal Hocko <mhocko@suse.com>
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 e8cb983..fbec74a 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2526,7 +2526,7 @@ static bool shrink_node(pg_data_t *pgdat, struct scan_control *sc)
 					sc->memcg_low_skipped = 1;
 					continue;
 				}
-				mem_cgroup_events(memcg, MEMCG_LOW, 1);
+				mem_cgroup_event(memcg, MEMCG_LOW);
 			}
 
 			reclaimed = sc->nr_reclaimed;