BACKPORT: mm: fix pageblock heuristic

The Android-tuned page block heuristic was accidentally reset in an AU
drop. Fix the heuristic to avoid unnecessary unmovable pageblock
migration over time.

bug 30643938
Bug: 63336523
(cherry-picked from commit 3e19bcf7d08713daaaba888b4d13502e06e38e96)
Change-Id: I59efcd3934f29982b1c9aeb7b0f18eb17e0934b3
Signed-off-by: John Dias <joaodias@google.com>

mm/compaction.c

@@ -1345,7 +1345,7 @@ static int __compact_finished(struct zone *zone, struct compact_control *cc,
 		 * other migratetype buddy lists.
 		 */
 		if (find_suitable_fallback(area, order, migratetype,
-						true, &can_steal) != -1)
+					   true, cc->order, &can_steal) != -1)
 			return COMPACT_PARTIAL;
 	}
 

mm/internal.h

@@ -226,9 +226,9 @@ isolate_freepages_range(struct compact_control *cc,
 unsigned long
 isolate_migratepages_range(struct compact_control *cc,
 			   unsigned long low_pfn, unsigned long end_pfn);
-int find_suitable_fallback(struct free_area *area, unsigned int order,
-			int migratetype, bool only_stealable, bool *can_steal);
-
+int find_suitable_fallback(struct free_area *area, unsigned int current_order,
+			   int migratetype, bool only_stealable,
+			   int start_order, bool *can_steal);
 #endif
 
 /*

mm/page_alloc.c

@@ -1655,7 +1655,8 @@ static void change_pageblock_range(struct page *pageblock_page,
  * is worse than movable allocations stealing from unmovable and reclaimable
  * pageblocks.
  */
-static bool can_steal_fallback(unsigned int order, int start_mt)
+static bool can_steal_fallback(unsigned int current_order, unsigned int start_order,
+			       int start_mt, int fallback_mt)
 {
 	/*
 	 * Leaving this order check is intended, although there is
@@ -1664,12 +1665,17 @@ static bool can_steal_fallback(unsigned int order, int start_mt)
 	 * but, below check doesn't guarantee it and that is just heuristic
 	 * so could be changed anytime.
 	 */
-	if (order >= pageblock_order)
+	if (current_order >= pageblock_order)
 		return true;
 
-	if (order >= pageblock_order / 2 ||
+	/* don't let unmovable allocations cause migrations simply because of free pages */
+	if ((start_mt != MIGRATE_UNMOVABLE && current_order >= pageblock_order / 2) ||
+	        /* only steal reclaimable page blocks for unmovable allocations */
+	        (start_mt == MIGRATE_UNMOVABLE && fallback_mt != MIGRATE_MOVABLE && current_order >= pageblock_order / 2) ||
+	        /* reclaimable can steal aggressively */
 		start_mt == MIGRATE_RECLAIMABLE ||
-		start_mt == MIGRATE_UNMOVABLE ||
+		/* allow unmovable allocs up to 64K without migrating blocks */
+		(start_mt == MIGRATE_UNMOVABLE && start_order >= 5) ||
 		page_group_by_mobility_disabled)
 		return true;
 
@@ -1709,8 +1715,9 @@ static void steal_suitable_fallback(struct zone *zone, struct page *page,
  * we can steal other freepages all together. This would help to reduce
  * fragmentation due to mixed migratetype pages in one pageblock.
  */
-int find_suitable_fallback(struct free_area *area, unsigned int order,
-			int migratetype, bool only_stealable, bool *can_steal)
+int find_suitable_fallback(struct free_area *area, unsigned int current_order,
+			   int migratetype, bool only_stealable,
+			   int start_order, bool *can_steal)
 {
 	int i;
 	int fallback_mt;
@@ -1727,7 +1734,7 @@ int find_suitable_fallback(struct free_area *area, unsigned int order,
 		if (list_empty(&area->free_list[fallback_mt]))
 			continue;
 
-		if (can_steal_fallback(order, migratetype))
+		if (can_steal_fallback(current_order, start_order, migratetype, fallback_mt))
 			*can_steal = true;
 
 		if (!only_stealable)
@@ -1863,7 +1870,7 @@ __rmqueue_fallback(struct zone *zone, unsigned int order, int start_migratetype)
 				--current_order) {
 		area = &(zone->free_area[current_order]);
 		fallback_mt = find_suitable_fallback(area, current_order,
-				start_migratetype, false, &can_steal);
+				start_migratetype, false, order, &can_steal);
 		if (fallback_mt == -1)
 			continue;