memcg: convert to use zone_to_nid() from bare zone->zone_pgdat->node_id

We have zone_to_nid().  this patch convert all existing users of
zone->zone_pgdat->node_id.
Signed-off-by: NKOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Acked-by: NBalbir Singh <balbir@linux.vnet.ibm.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Nishimura Daisuke <d-nishimura@mtf.biglobe.ne.jp>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

mm/memcontrol.c

@@ -919,7 +919,7 @@ unsigned long mem_cgroup_zone_nr_pages(struct mem_cgroup *memcg,
 				       struct zone *zone,
 				       enum lru_list lru)
 {
-	int nid = zone->zone_pgdat->node_id;
+	int nid = zone_to_nid(zone);
 	int zid = zone_idx(zone);
 	struct mem_cgroup_per_zone *mz = mem_cgroup_zoneinfo(memcg, nid, zid);
 
@@ -929,7 +929,7 @@ unsigned long mem_cgroup_zone_nr_pages(struct mem_cgroup *memcg,
 struct zone_reclaim_stat *mem_cgroup_get_reclaim_stat(struct mem_cgroup *memcg,
 						      struct zone *zone)
 {
-	int nid = zone->zone_pgdat->node_id;
+	int nid = zone_to_nid(zone);
 	int zid = zone_idx(zone);
 	struct mem_cgroup_per_zone *mz = mem_cgroup_zoneinfo(memcg, nid, zid);
 
@@ -974,7 +974,7 @@ unsigned long mem_cgroup_isolate_pages(unsigned long nr_to_scan,
 	LIST_HEAD(pc_list);
 	struct list_head *src;
 	struct page_cgroup *pc, *tmp;
-	int nid = z->zone_pgdat->node_id;
+	int nid = zone_to_nid(z);
 	int zid = zone_idx(z);
 	struct mem_cgroup_per_zone *mz;
 	int lru = LRU_FILE * file + active;