[PATCH v2 2/3] mm: remain migratetype in freed page

[Minchan Kim <minchan@kernel.org>]

The page allocator caches the pageblock information in page->private while
it is in the PCP freelists but this is overwritten with the order of the
page when freed to the buddy allocator. This patch stores the migratetype
of the page in the page->index field so that it is available at all times
when the page remain in free_list.

This patch adds a new call site in __free_pages_ok so it might be
overhead a bit but it's for high order allocation.
So I believe damage isn't hurt.

* from v1
  * Fix move_freepages's migratetype - Mel
  * Add more kind explanation in description - Mel

Signed-off-by: Minchan Kim <minchan@kernel.org>
---
 include/linux/mm.h |    4 ++--
 mm/page_alloc.c    |    7 +++++--
 2 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 84d1663f..68f9e8d 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -240,13 +240,13 @@ struct inode;
 /* It's valid only if the page is free path or free_list */
 static inline void set_freepage_migratetype(struct page *page, int migratetype)
 {
-	set_page_private(page, migratetype);
+	page->index = migratetype;
 }
 
 /* It's valid only if the page is free path or free_list */
 static inline int get_freepage_migratetype(struct page *page)
 {
-	return page_private(page);
+	return page->index;
 }
 
 /*
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index f5ba236..8531fa3 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -723,6 +723,7 @@ static void __free_pages_ok(struct page *page, unsigned int order)
 {
 	unsigned long flags;
 	int wasMlocked = __TestClearPageMlocked(page);
+	int migratetype;
 
 	if (!free_pages_prepare(page, order))
 		return;
@@ -731,8 +732,9 @@ static void __free_pages_ok(struct page *page, unsigned int order)
 	if (unlikely(wasMlocked))
 		free_page_mlock(page);
 	__count_vm_events(PGFREE, 1 << order);
-	free_one_page(page_zone(page), page, order,
-					get_pageblock_migratetype(page));
+	migratetype = get_pageblock_migratetype(page);
+	set_freepage_migratetype(page, migratetype);
+	free_one_page(page_zone(page), page, order, migratetype);
 	local_irq_restore(flags);
 }
 
@@ -952,6 +954,7 @@ static int move_freepages(struct zone *zone,
 		order = page_order(page);
 		list_move(&page->lru,
 			  &zone->free_area[order].free_list[migratetype]);
+		set_freepage_migratetype(page, migratetype);
 		page += 1 << order;
 		pages_moved += 1 << order;
 	}
-- 
1.7.9.5