vmscan: recalculate lru_pages on each priority

shrink_zones() need relatively long time and lru_pages can change
dramatically during shrink_zones().  So lru_pages should be recalculated
for each priority.
Signed-off-by: NKOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Acked-by: NRik van Riel <riel@redhat.com>
Reviewed-by: NMinchan Kim <minchan.kim@gmail.com>
Acked-by: NJohannes Weiner <hannes@cmpxchg.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

mm/vmscan.c

@@ -1787,7 +1787,6 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
 	bool all_unreclaimable;
 	unsigned long total_scanned = 0;
 	struct reclaim_state *reclaim_state = current->reclaim_state;
-	unsigned long lru_pages = 0;
 	struct zoneref *z;
 	struct zone *zone;
 	enum zone_type high_zoneidx = gfp_zone(sc->gfp_mask);
@@ -1798,18 +1797,6 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
 
 	if (scanning_global_lru(sc))
 		count_vm_event(ALLOCSTALL);
-	/*
-	 * mem_cgroup will not do shrink_slab.
-	 */
-	if (scanning_global_lru(sc)) {
-		for_each_zone_zonelist(zone, z, zonelist, high_zoneidx) {
-
-			if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
-				continue;
-
-			lru_pages += zone_reclaimable_pages(zone);
-		}
-	}
 
 	for (priority = DEF_PRIORITY; priority >= 0; priority--) {
 		sc->nr_scanned = 0;
@@ -1821,6 +1808,14 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
 		 * over limit cgroups
 		 */
 		if (scanning_global_lru(sc)) {
+			unsigned long lru_pages = 0;
+			for_each_zone_zonelist(zone, z, zonelist, high_zoneidx) {
+				if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
+					continue;
+
+				lru_pages += zone_reclaimable_pages(zone);
+			}
+
 			shrink_slab(sc->nr_scanned, sc->gfp_mask, lru_pages);
 			if (reclaim_state) {
 				sc->nr_reclaimed += reclaim_state->reclaimed_slab;