mm: memcontrol: report kernel stack usage in cgroup2 memory.stat

Show how much memory is allocated to kernel stacks.

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/Documentation/cgroup-v2.txt b/Documentation/cgroup-v2.txt
index e4e0c1d..e2f4e79 100644
--- a/Documentation/cgroup-v2.txt
+++ b/Documentation/cgroup-v2.txt
@@ -843,6 +843,10 @@
 		Amount of memory used to cache filesystem data,
 		including tmpfs and shared memory.
 
+	  kernel_stack
+
+		Amount of memory allocated to kernel stacks.
+
 	  slab
 
 		Amount of memory used for storing in-kernel data