[PATCH] shrink_all_memory(): fix lru_pages handling

At the end of shrink_all_memory() we forget to recalculate lru_pages: it can
be zero.

Fix that up, and add a helper function for this operation too.

Also, recalculate lru_pages each time around the inner loop to get the
balancing correct.

Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
Cc: Pavel Machek <pavel@ucw.cz>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

mm/vmscan.c

@@ -1406,6 +1406,16 @@ static unsigned long shrink_all_zones(unsigned long nr_pages, int prio,
 	return ret;
 }
 
+static unsigned long count_lru_pages(void)
+{
+	struct zone *zone;
+	unsigned long ret = 0;
+
+	for_each_zone(zone)
+		ret += zone->nr_active + zone->nr_inactive;
+	return ret;
+}
+
 /*
  * Try to free `nr_pages' of memory, system-wide, and return the number of
  * freed pages.
@@ -1420,7 +1430,6 @@ unsigned long shrink_all_memory(unsigned long nr_pages)
 	unsigned long ret = 0;
 	int pass;
 	struct reclaim_state reclaim_state;
-	struct zone *zone;
 	struct scan_control sc = {
 		.gfp_mask = GFP_KERNEL,
 		.may_swap = 0,
@@ -1431,10 +1440,7 @@ unsigned long shrink_all_memory(unsigned long nr_pages)
 
 	current->reclaim_state = &reclaim_state;
 
-	lru_pages = 0;
-	for_each_zone(zone)
-		lru_pages += zone->nr_active + zone->nr_inactive;
-
+	lru_pages = count_lru_pages();
 	nr_slab = global_page_state(NR_SLAB_RECLAIMABLE);
 	/* If slab caches are huge, it's better to hit them first */
 	while (nr_slab >= lru_pages) {
@@ -1461,13 +1467,6 @@ unsigned long shrink_all_memory(unsigned long nr_pages)
 	for (pass = 0; pass < 5; pass++) {
 		int prio;
 
-		/* Needed for shrinking slab caches later on */
-		if (!lru_pages)
-			for_each_zone(zone) {
-				lru_pages += zone->nr_active;
-				lru_pages += zone->nr_inactive;
-			}
-
 		/* Force reclaiming mapped pages in the passes #3 and #4 */
 		if (pass > 2) {
 			sc.may_swap = 1;
@@ -1483,7 +1482,8 @@ unsigned long shrink_all_memory(unsigned long nr_pages)
 				goto out;
 
 			reclaim_state.reclaimed_slab = 0;
-			shrink_slab(sc.nr_scanned, sc.gfp_mask, lru_pages);
+			shrink_slab(sc.nr_scanned, sc.gfp_mask,
+					count_lru_pages());
 			ret += reclaim_state.reclaimed_slab;
 			if (ret >= nr_pages)
 				goto out;
@@ -1491,20 +1491,19 @@ unsigned long shrink_all_memory(unsigned long nr_pages)
 			if (sc.nr_scanned && prio < DEF_PRIORITY - 2)
 				congestion_wait(WRITE, HZ / 10);
 		}
-
-		lru_pages = 0;
 	}
 
 	/*
 	 * If ret = 0, we could not shrink LRUs, but there may be something
 	 * in slab caches
 	 */
-	if (!ret)
+	if (!ret) {
 		do {
 			reclaim_state.reclaimed_slab = 0;
-			shrink_slab(nr_pages, sc.gfp_mask, lru_pages);
+			shrink_slab(nr_pages, sc.gfp_mask, count_lru_pages());
 			ret += reclaim_state.reclaimed_slab;
 		} while (ret < nr_pages && reclaim_state.reclaimed_slab > 0);
+	}
 
 out:
 	current->reclaim_state = NULL;