Be more agressive about stealing when MIGRATE_RECLAIMABLE allocations fallback

MIGRATE_RECLAIMABLE allocations tend to be very bursty in nature like when
updatedb starts.  It is likely this will occur in situations where MAX_ORDER
blocks of pages are not free.  This means that updatedb can scatter
MIGRATE_RECLAIMABLE pages throughout the address space.  This patch is more
agressive about stealing blocks of pages for MIGRATE_RECLAIMABLE.
Signed-off-by: NMel Gorman <mel@csn.ul.ie>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

mm/page_alloc.c

@@ -821,11 +821,23 @@ static struct page *__rmqueue_fallback(struct zone *zone, int order,
 
 			/*
 			 * If breaking a large block of pages, move all free
-			 * pages to the preferred allocation list
-			 */
-			if (unlikely(current_order >= MAX_ORDER / 2)) {
+			 * pages to the preferred allocation list. If falling
+			 * back for a reclaimable kernel allocation, be more
+			 * agressive about taking ownership of free pages
+			 */
+			if (unlikely(current_order >= MAX_ORDER / 2) ||
+					start_migratetype == MIGRATE_RECLAIMABLE) {
+				unsigned long pages;
+				pages = move_freepages_block(zone, page,
+								start_migratetype);
+
+				/* Claim the whole block if over half of it is free */
+				if ((pages << current_order) >= (1 << (MAX_ORDER-2)) &&
+						migratetype != MIGRATE_HIGHATOMIC)
+					set_pageblock_migratetype(page,
+								start_migratetype);
+
 				migratetype = start_migratetype;
-				move_freepages_block(zone, page, migratetype);
 			}
 
 			/* Remove the page from the freelists */