mm/page_alloc: fix freeing of MIGRATE_RESERVE migratetype pages

mm/page_alloc: fix freeing of MIGRATE_RESERVE migratetype pages

Pages allocated from MIGRATE_RESERVE migratetype pageblocks
are not freed back to MIGRATE_RESERVE migratetype free
lists in free_pcppages_bulk()->__free_one_page() if we got
to free_pcppages_bulk() through drain_[zone_]pages().
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>
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Change-Id: I1d4ab2a3241387160dd376b0ead864cd2b0c59f0