[RFC][PATCH] mm/page_alloc: fix freeing of MIGRATE_RESERVE migratetype pages

[Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>]

Pages allocated from MIGRATE_RESERVE migratetype pageblocks
are not freed back to MIGRATE_RESERVE migratetype free
lists in free_pcppages_bulk() if we got to that function
through drain_[zone_]pages() or __zone_pcp_update().
The freeing through free_hot_cold_page() is okay because
freepage migratetype is set to pageblock migratetype before
calling free_pcppages_bulk().  If pages of MIGRATE_RESERVE
migratetype end up on the free lists of other migratetype
whole Reserved pageblock may be later changed to the other
migratetype in __rmqueue_fallback() and it will be never
changed back to be a Reserved pageblock.  Fix the issue by
preserving freepage migratetype as a pageblock migratetype
(instead of overriding it to the requested migratetype)
for MIGRATE_RESERVE migratetype pages in rmqueue_bulk().

The problem was introduced in v2.6.31 by commit ed0ae21
("page allocator: do not call get_pageblock_migratetype()
more than necessary").

Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Reported-by: Yong-Taek Lee <ytk.lee@samsung.com>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Hugh Dickins <hughd@google.com>
---
 include/linux/mmzone.h |    5 +++++
 mm/page_alloc.c        |   10 +++++++---
 2 files changed, 12 insertions(+), 3 deletions(-)

Index: b/include/linux/mmzone.h
===================================================================
--- a/include/linux/mmzone.h	2014-02-14 18:59:08.177837747 +0100
+++ b/include/linux/mmzone.h	2014-02-14 18:59:09.077837731 +0100
@@ -63,6 +63,11 @@ enum {
 	MIGRATE_TYPES
 };
 
+static inline bool is_migrate_reserve(int migratetype)
+{
+	return unlikely(migratetype == MIGRATE_RESERVE);
+}
+
 #ifdef CONFIG_CMA
 #  define is_migrate_cma(migratetype) unlikely((migratetype) == MIGRATE_CMA)
 #else
Index: b/mm/page_alloc.c
===================================================================
--- a/mm/page_alloc.c	2014-02-14 18:59:08.185837746 +0100
+++ b/mm/page_alloc.c	2014-02-14 18:59:09.077837731 +0100
@@ -1174,7 +1174,7 @@ static int rmqueue_bulk(struct zone *zon
 			unsigned long count, struct list_head *list,
 			int migratetype, int cold)
 {
-	int mt = migratetype, i;
+	int mt, i;
 
 	spin_lock(&zone->lock);
 	for (i = 0; i < count; ++i) {
@@ -1195,9 +1195,13 @@ static int rmqueue_bulk(struct zone *zon
 			list_add(&page->lru, list);
 		else
 			list_add_tail(&page->lru, list);
+		mt = get_pageblock_migratetype(page);
 		if (IS_ENABLED(CONFIG_CMA)) {
-			mt = get_pageblock_migratetype(page);
-			if (!is_migrate_cma(mt) && !is_migrate_isolate(mt))
+			if (!is_migrate_cma(mt) && !is_migrate_isolate(mt) &&
+			    !is_migrate_reserve(mt))
+				mt = migratetype;
+		} else {
+			if (!is_migrate_reserve(mt))
 				mt = migratetype;
 		}
 		set_freepage_migratetype(page, mt);