mm/vmscan: push zone pointer into shrink_page_list()

It doesn't need a pointer to the cgroup - pointer to the zone is enough.
This patch also kills the "mz" argument of page_check_references() - it is
unused after "mm: memcg: count pte references from every member of the
reclaimed hierarch"
Signed-off-by: Konstantin Khlebnikov <khlebnikov@openvz.org>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/vmscan.c

@@ -629,7 +629,6 @@ enum page_references {
 };
 
 static enum page_references page_check_references(struct page *page,
-						  struct mem_cgroup_zone *mz,
 						  struct scan_control *sc)
 {
 	int referenced_ptes, referenced_page;
@@ -688,7 +687,7 @@ static enum page_references page_check_references(struct page *page,
  * shrink_page_list() returns the number of reclaimed pages
  */
 static unsigned long shrink_page_list(struct list_head *page_list,
-				      struct mem_cgroup_zone *mz,
+				      struct zone *zone,
 				      struct scan_control *sc,
 				      unsigned long *ret_nr_dirty,
 				      unsigned long *ret_nr_writeback)
@@ -718,7 +717,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
 			goto keep;
 
 		VM_BUG_ON(PageActive(page));
-		VM_BUG_ON(page_zone(page) != mz->zone);
+		VM_BUG_ON(page_zone(page) != zone);
 
 		sc->nr_scanned++;
 
@@ -741,7 +740,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
 			goto keep;
 		}
 
-		references = page_check_references(page, mz, sc);
+		references = page_check_references(page, sc);
 		switch (references) {
 		case PAGEREF_ACTIVATE:
 			goto activate_locked;
@@ -931,7 +930,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
 	 * will encounter the same problem
 	 */
 	if (nr_dirty && nr_dirty == nr_congested && global_reclaim(sc))
-		zone_set_flag(mz->zone, ZONE_CONGESTED);
+		zone_set_flag(zone, ZONE_CONGESTED);
 
 	free_hot_cold_page_list(&free_pages, 1);
 
@@ -1309,7 +1308,7 @@ shrink_inactive_list(unsigned long nr_to_scan, struct mem_cgroup_zone *mz,
 
 	update_isolated_counts(mz, &page_list, &nr_anon, &nr_file);
 
-	nr_reclaimed = shrink_page_list(&page_list, mz, sc,
+	nr_reclaimed = shrink_page_list(&page_list, zone, sc,
 						&nr_dirty, &nr_writeback);
 
 	spin_lock_irq(&zone->lru_lock);