mm: memcontrol: add "sock" to cgroup2 memory.stat

Provide statistics on how much of a cgroup's memory footprint is made up
of socket buffers from network connections owned by the group.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Vladimir Davydov <vdavydov@virtuozzo.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>
diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 1666617..9ae48d4 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -50,6 +50,9 @@
 	MEM_CGROUP_STAT_WRITEBACK,	/* # of pages under writeback */
 	MEM_CGROUP_STAT_SWAP,		/* # of pages, swapped out */
 	MEM_CGROUP_STAT_NSTATS,
+	/* default hierarchy stats */
+	MEMCG_SOCK,
+	MEMCG_NR_STAT,
 };
 
 struct mem_cgroup_reclaim_cookie {
@@ -87,7 +90,7 @@
 
 #ifdef CONFIG_MEMCG
 struct mem_cgroup_stat_cpu {
-	long count[MEM_CGROUP_STAT_NSTATS];
+	long count[MEMCG_NR_STAT];
 	unsigned long events[MEMCG_NR_EVENTS];
 	unsigned long nr_page_events;
 	unsigned long targets[MEM_CGROUP_NTARGETS];