mm: memcontrol: give the kmem states more descriptive names

On any given memcg, the kmem accounting feature has three separate
states: not initialized, structures allocated, and actively accounting
slab memory.  These are represented through a combination of the
kmem_acct_activated and kmem_acct_active flags, which is confusing.

Convert to a kmem_state enum with the states NONE, ALLOCATED, and
ONLINE.  Then rename the functions to modify the state accordingly.
This follows the nomenclature of css object states more closely.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Tejun Heo <tj@kernel.org>
Acked-by: Vladimir Davydov <vdavydov@virtuozzo.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/slab_common.c b/mm/slab_common.c
index e016178..8c262e6 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -503,10 +503,10 @@
 	mutex_lock(&slab_mutex);
 
 	/*
-	 * The memory cgroup could have been deactivated while the cache
+	 * The memory cgroup could have been offlined while the cache
 	 * creation work was pending.
 	 */
-	if (!memcg_kmem_is_active(memcg))
+	if (!memcg_kmem_online(memcg))
 		goto out_unlock;
 
 	idx = memcg_cache_id(memcg);