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

[Minchan Kim <minchan@kernel.org>]

Page allocator doesn't keep migratetype information to page
when the page is freed. This patch remains the information
to freed page's index field which isn't used by free/alloc
preparing so it shouldn't change any behavir except below one.

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.

Signed-off-by: Minchan Kim <minchan@kernel.org>
---
 include/linux/mm.h |    6 ++++--
 mm/page_alloc.c    |    7 ++++---
 2 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 86d61d6..8fd32da 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -251,12 +251,14 @@ struct inode;
 
 static inline void set_page_migratetype(struct page *page, int migratetype)
 {
-	set_page_private(page, migratetype);
+	VM_BUG_ON((unsigned int)migratetype >= MIGRATE_TYPES);
+	page->index = migratetype;
 }
 
 static inline int get_page_migratetype(struct page *page)
 {
-	return page_private(page);
+	VM_BUG_ON((unsigned int)page->index >= MIGRATE_TYPES);
+	return page->index;
 }
 
 /*
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 103ba66..32985dd 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;
@@ -731,9 +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_page_migratetype(page, migratetype);
+	free_one_page(page_zone(page), page, order, migratetype);
 	local_irq_restore(flags);
 }
 
-- 
1.7.9.5