mm: memcg: group swapped-out statistics counter logically

The counter of currently swapped out pages in a memcg (hierarchy) is
sitting amidst ever-increasing event counters.  Move this item to the
other counters that reflect current state rather than history.

This technically breaks the kernel ABI, but hopefully nobody relies on the
order of items in memory.stat.

Signed-off-by: Johannes Weiner <[email protected]>
Acked-by: Michal Hocko <[email protected]>
Acked-by: KAMEZAWA Hiroyuki <[email protected]>
Cc: Ying Han <[email protected]>
Cc: Tejun Heo <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

mm/memcontrol.c

@@ -4043,9 +4043,9 @@ enum {
 	MCS_CACHE,
 	MCS_RSS,
 	MCS_FILE_MAPPED,
+	MCS_SWAP,
 	MCS_PGPGIN,
 	MCS_PGPGOUT,
-	MCS_SWAP,
 	MCS_PGFAULT,
 	MCS_PGMAJFAULT,
 	MCS_INACTIVE_ANON,
@@ -4064,9 +4064,9 @@ static const char *memcg_stat_strings[NR_MCS_STAT] = {
 	"cache",
 	"rss",
 	"mapped_file",
+	"swap",
 	"pgpgin",
 	"pgpgout",
-	"swap",
 	"pgfault",
 	"pgmajfault",
 	"inactive_anon",