[PATCH 7/7] mm/page_alloc: don't merge MIGRATE_(CMA|ISOLATE) pages on buddy

[Joonsoo Kim <iamjoonsoo.kim@lge.com>]

If (MAX_ORDER-1) is greater than pageblock order, there is a possibility
to merge different migratetype pages and to be linked in unintended
freelist.

While I test CMA, CMA pages are merged and linked into MOVABLE freelist
by above issue and then, the pages change their migratetype to UNMOVABLE by
try_to_steal_freepages(). After that, CMA to this region always fail.

To prevent this, we should not merge the page on MIGRATE_(CMA|ISOLATE)
freelist.

Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 2548b42..ea99cee 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -581,6 +581,15 @@ static inline void __free_one_page(struct page *page,
 			__mod_zone_freepage_state(zone, 1 << order,
 						  migratetype);
 		} else {
+			int buddy_mt = get_buddy_migratetype(buddy);
+
+			/* We don't want to merge cma, isolate pages */
+			if (unlikely(order >= pageblock_order) &&
+				migratetype != buddy_mt &&
+				(migratetype >= MIGRATE_PCPTYPES ||
+				buddy_mt >= MIGRATE_PCPTYPES)) {
+				break;
+			}
 			list_del(&buddy->lru);
 			zone->free_area[order].nr_free--;
 			rmv_page_order(buddy);
-- 
1.7.9.5

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