1 files changed, 52 insertions, 14 deletions

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index bd65b60939b6..64b7d82a9b1a 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2206,19 +2206,26 @@ static bool unreserve_highatomic_pageblock(const struct alloc_context *ac,
  * list of requested migratetype, possibly along with other pages from the same
  * block, depending on fragmentation avoidance heuristics. Returns true if
  * fallback was found so that __rmqueue_smallest() can grab it.
+ *
+ * The use of signed ints for order and current_order is a deliberate
+ * deviation from the rest of this file, to make the for loop
+ * condition simpler.
  */
 static inline bool
-__rmqueue_fallback(struct zone *zone, unsigned int order, int start_migratetype)
+__rmqueue_fallback(struct zone *zone, int order, int start_migratetype)
 {
 	struct free_area *area;
-	unsigned int current_order;
+	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;
+	/*
+	 * Find the largest available free page in the other list. This roughly
+	 * approximates finding the pageblock with the most free pages, which
+	 * would be too costly to do exactly.
+	 */
+	for (current_order = MAX_ORDER - 1; current_order >= order;
 				--current_order) {
 		area = &(zone->free_area[current_order]);
 		fallback_mt = find_suitable_fallback(area, current_order,
@@ -2226,19 +2233,50 @@ __rmqueue_fallback(struct zone *zone, unsigned int order, int start_migratetype)
 		if (fallback_mt == -1)
 			continue;
 
-		page = list_first_entry(&area->free_list[fallback_mt],
-						struct page, lru);
+		/*
+		 * We cannot steal all free pages from the pageblock and the
+		 * requested migratetype is movable. In that case it's better to
+		 * steal and split the smallest available page instead of the
+		 * largest available page, because even if the next movable
+		 * allocation falls back into a different pageblock than this
+		 * one, it won't cause permanent fragmentation.
+		 */
+		if (!can_steal && start_migratetype == MIGRATE_MOVABLE
+					&& current_order > order)
+			goto find_smallest;
 
-		steal_suitable_fallback(zone, page, start_migratetype,
-								can_steal);
+		goto do_steal;
+	}
 
-		trace_mm_page_alloc_extfrag(page, order, current_order,
-			start_migratetype, fallback_mt);
+	return false;
 
-		return true;
+find_smallest:
+	for (current_order = order; current_order < MAX_ORDER;
+							current_order++) {
+		area = &(zone->free_area[current_order]);
+		fallback_mt = find_suitable_fallback(area, current_order,
+				start_migratetype, false, &can_steal);
+		if (fallback_mt != -1)
+			break;
 	}
 
-	return false;
+	/*
+	 * This should not happen - we already found a suitable fallback
+	 * when looking for the largest page.
+	 */
+	VM_BUG_ON(current_order == MAX_ORDER);
+
+do_steal:
+	page = list_first_entry(&area->free_list[fallback_mt],
+							struct page, lru);
+
+	steal_suitable_fallback(zone, page, start_migratetype, can_steal);
+
+	trace_mm_page_alloc_extfrag(page, order, current_order,
+		start_migratetype, fallback_mt);
+
+	return true;
+
 }
 
 /*
@@ -5240,7 +5278,7 @@ void __ref build_all_zonelists(pg_data_t *pgdat, struct zone *zone)
 #endif
 		/* we have to stop all cpus to guarantee there is no user
 		   of zonelist */
-		stop_machine(__build_all_zonelists, pgdat, NULL);
+		stop_machine_cpuslocked(__build_all_zonelists, pgdat, NULL);
 		/* cpuset refresh routine should be here */
 	}
 	vm_total_pages = nr_free_pagecache_pages();