memcg: move memcg_stock initialization to mem_cgroup_init

memcg_stock are currently initialized during the root cgroup allocation
which is OK but it pointlessly pollutes memcg allocation code with
something that can be called when the memcg subsystem is initialized by
mem_cgroup_init along with other controller specific parts.

This patch wraps the current memcg_stock initialization code into a
helper calls it from the controller subsystem initialization code.
Signed-off-by: Michal Hocko <mhocko@suse.cz>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Tejun Heo <htejun@gmail.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/memcontrol.c

@@ -2296,6 +2296,17 @@ static void drain_local_stock(struct work_struct *dummy)
 	clear_bit(FLUSHING_CACHED_CHARGE, &stock->flags);
 }
 
+static void __init memcg_stock_init(void)
+{
+	int cpu;
+
+	for_each_possible_cpu(cpu) {
+		struct memcg_stock_pcp *stock =
+					&per_cpu(memcg_stock, cpu);
+		INIT_WORK(&stock->work, drain_local_stock);
+	}
+}
+
 /*
  * Cache charges(val) which is from res_counter, to local per_cpu area.
  * This will be consumed by consume_stock() function, later.
@@ -6092,15 +6103,7 @@ mem_cgroup_css_alloc(struct cgroup *cont)
 
 	/* root ? */
 	if (cont->parent == NULL) {
-		int cpu;
-
 		root_mem_cgroup = memcg;
-		for_each_possible_cpu(cpu) {
-			struct memcg_stock_pcp *stock =
-						&per_cpu(memcg_stock, cpu);
-			INIT_WORK(&stock->work, drain_local_stock);
-		}
-
 		res_counter_init(&memcg->res, NULL);
 		res_counter_init(&memcg->memsw, NULL);
 		res_counter_init(&memcg->kmem, NULL);
@@ -6837,6 +6840,7 @@ static int __init mem_cgroup_init(void)
 	hotcpu_notifier(memcg_cpu_hotplug_callback, 0);
 	enable_swap_cgroup();
 	mem_cgroup_soft_limit_tree_init();
+	memcg_stock_init();
 	return 0;
 }
 subsys_initcall(mem_cgroup_init);