memcg: do not account memory used for cache creation

The memory we used to hold the memcg arrays is currently accounted to
the current memcg.  But that creates a problem, because that memory can
only be freed after the last user is gone.  Our only way to know which
is the last user, is to hook up to freeing time, but the fact that we
still have some in flight kmallocs will prevent freeing to happen.  I
believe therefore to be just easier to account this memory as global
overhead.

Signed-off-by: Glauber Costa <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Kamezawa Hiroyuki <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

mm/memcontrol.c

@@ -5232,7 +5232,9 @@ static int memcg_propagate_kmem(struct mem_cgroup *memcg)
 	static_key_slow_inc(&memcg_kmem_enabled_key);
 
 	mutex_lock(&set_limit_mutex);
+	memcg_stop_kmem_account();
 	ret = memcg_update_cache_sizes(memcg);
+	memcg_resume_kmem_account();
 	mutex_unlock(&set_limit_mutex);
 out:
 	return ret;