mm: memcg: remove obsolete statistics array boundary enum item

MEM_CGROUP_STAT_DATA is a leftover from when item counters were living in
the same array as ever-increasing event counters.  It's no longer needed,
use MEM_CGROUP_STAT_NSTATS to iterate over the stat array.
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Michal Hocko <mhocko@suse.cz>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Ying Han <yinghan@google.com>
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

@@ -88,7 +88,6 @@ enum mem_cgroup_stat_index {
 	MEM_CGROUP_STAT_RSS,	   /* # of pages charged as anon rss */
 	MEM_CGROUP_STAT_FILE_MAPPED,  /* # of pages charged as file rss */
 	MEM_CGROUP_STAT_SWAPOUT, /* # of pages, swapped out */
-	MEM_CGROUP_STAT_DATA, /* end of data requires synchronization */
 	MEM_CGROUP_STAT_NSTATS,
 };
 
@@ -2135,7 +2134,7 @@ static void mem_cgroup_drain_pcp_counter(struct mem_cgroup *memcg, int cpu)
 	int i;
 
 	spin_lock(&memcg->pcp_counter_lock);
-	for (i = 0; i < MEM_CGROUP_STAT_DATA; i++) {
+	for (i = 0; i < MEM_CGROUP_STAT_NSTATS; i++) {
 		long x = per_cpu(memcg->stat->count[i], cpu);
 
 		per_cpu(memcg->stat->count[i], cpu) = 0;