1 files changed, 91 insertions, 52 deletions

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 9ca626756927..31aa943365d8 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1145,14 +1145,40 @@ static void change_pageblock_range(struct page *pageblock_page,
  * as fragmentation caused by those allocations polluting movable pageblocks
  * is worse than movable allocations stealing from unmovable and reclaimable
  * pageblocks.
- *
- * If we claim more than half of the pageblock, change pageblock's migratetype
- * as well.
  */
-static void try_to_steal_freepages(struct zone *zone, struct page *page,
-				  int start_type, int fallback_type)
+static bool can_steal_fallback(unsigned int order, int start_mt)
+{
+	/*
+	 * Leaving this order check is intended, although there is
+	 * relaxed order check in next check. The reason is that
+	 * we can actually steal whole pageblock if this condition met,
+	 * but, below check doesn't guarantee it and that is just heuristic
+	 * so could be changed anytime.
+	 */
+	if (order >= pageblock_order)
+		return true;
+
+	if (order >= pageblock_order / 2 ||
+		start_mt == MIGRATE_RECLAIMABLE ||
+		start_mt == MIGRATE_UNMOVABLE ||
+		page_group_by_mobility_disabled)
+		return true;
+
+	return false;
+}
+
+/*
+ * This function implements actual steal behaviour. If order is large enough,
+ * we can steal whole pageblock. If not, we first move freepages in this
+ * pageblock and check whether half of pages are moved or not. If half of
+ * pages are moved, we can change migratetype of pageblock and permanently
+ * use it's pages as requested migratetype in the future.
+ */
+static void steal_suitable_fallback(struct zone *zone, struct page *page,
+							  int start_type)
 {
 	int current_order = page_order(page);
+	int pages;
 
 	/* Take ownership for orders >= pageblock_order */
 	if (current_order >= pageblock_order) {
@@ -1160,19 +1186,40 @@ static void try_to_steal_freepages(struct zone *zone, struct page *page,
 		return;
 	}
 
-	if (current_order >= pageblock_order / 2 ||
-	    start_type == MIGRATE_RECLAIMABLE ||
-	    start_type == MIGRATE_UNMOVABLE ||
-	    page_group_by_mobility_disabled) {
-		int pages;
+	pages = move_freepages_block(zone, page, start_type);
+
+	/* Claim the whole block if over half of it is free */
+	if (pages >= (1 << (pageblock_order-1)) ||
+			page_group_by_mobility_disabled)
+		set_pageblock_migratetype(page, start_type);
+}
+
+/* Check whether there is a suitable fallback freepage with requested order. */
+static int find_suitable_fallback(struct free_area *area, unsigned int order,
+					int migratetype, bool *can_steal)
+{
+	int i;
+	int fallback_mt;
+
+	if (area->nr_free == 0)
+		return -1;
+
+	*can_steal = false;
+	for (i = 0;; i++) {
+		fallback_mt = fallbacks[migratetype][i];
+		if (fallback_mt == MIGRATE_RESERVE)
+			break;
+
+		if (list_empty(&area->free_list[fallback_mt]))
+			continue;
 
-		pages = move_freepages_block(zone, page, start_type);
+		if (can_steal_fallback(order, migratetype))
+			*can_steal = true;
 
-		/* Claim the whole block if over half of it is free */
-		if (pages >= (1 << (pageblock_order-1)) ||
-				page_group_by_mobility_disabled)
-			set_pageblock_migratetype(page, start_type);
+		return fallback_mt;
 	}
+
+	return -1;
 }
 
 /* Remove an element from the buddy allocator from the fallback list */
@@ -1182,53 +1229,45 @@ __rmqueue_fallback(struct zone *zone, unsigned int order, int start_migratetype)
 	struct free_area *area;
 	unsigned int current_order;
 	struct page *page;
+	int fallback_mt;
+	bool can_steal;
 
 	/* Find the largest possible block of pages in the other list */
 	for (current_order = MAX_ORDER-1;
 				current_order >= order && current_order <= MAX_ORDER-1;
 				--current_order) {
-		int i;
-		for (i = 0;; i++) {
-			int migratetype = fallbacks[start_migratetype][i];
-			int buddy_type = start_migratetype;
-
-			/* MIGRATE_RESERVE handled later if necessary */
-			if (migratetype == MIGRATE_RESERVE)
-				break;
-
-			area = &(zone->free_area[current_order]);
-			if (list_empty(&area->free_list[migratetype]))
-				continue;
-
-			page = list_entry(area->free_list[migratetype].next,
-					struct page, lru);
-			area->nr_free--;
-
-			try_to_steal_freepages(zone, page, start_migratetype,
-								migratetype);
+		area = &(zone->free_area[current_order]);
+		fallback_mt = find_suitable_fallback(area, current_order,
+				start_migratetype, &can_steal);
+		if (fallback_mt == -1)
+			continue;
 
-			/* Remove the page from the freelists */
-			list_del(&page->lru);
-			rmv_page_order(page);
+		page = list_entry(area->free_list[fallback_mt].next,
+						struct page, lru);
+		if (can_steal)
+			steal_suitable_fallback(zone, page, start_migratetype);
 
-			expand(zone, page, order, current_order, area,
-					buddy_type);
+		/* Remove the page from the freelists */
+		area->nr_free--;
+		list_del(&page->lru);
+		rmv_page_order(page);
 
-			/*
-			 * The freepage_migratetype may differ from pageblock's
-			 * migratetype depending on the decisions in
-			 * try_to_steal_freepages(). This is OK as long as it
-			 * does not differ for MIGRATE_CMA pageblocks. For CMA
-			 * we need to make sure unallocated pages flushed from
-			 * pcp lists are returned to the correct freelist.
-			 */
-			set_freepage_migratetype(page, buddy_type);
+		expand(zone, page, order, current_order, area,
+					start_migratetype);
+		/*
+		 * The freepage_migratetype may differ from pageblock's
+		 * migratetype depending on the decisions in
+		 * try_to_steal_freepages(). This is OK as long as it
+		 * does not differ for MIGRATE_CMA pageblocks. For CMA
+		 * we need to make sure unallocated pages flushed from
+		 * pcp lists are returned to the correct freelist.
+		 */
+		set_freepage_migratetype(page, start_migratetype);
 
-			trace_mm_page_alloc_extfrag(page, order, current_order,
-				start_migratetype, migratetype);
+		trace_mm_page_alloc_extfrag(page, order, current_order,
+			start_migratetype, fallback_mt);
 
-			return page;
-		}
+		return page;
 	}
 
 	return NULL;