[PATCH] switch free memory back to MIGRATE_MOVABLE

[Shaohua Li]

When page is back to buddy and its order is bigger than pageblock_order, we can
switch its type to MIGRATE_MOVABLE. This can reduce fragmentation. The patch
has obvious effect when read a block device and then drop caches.

Signed-off-by: Shaohua Li <shaohua.li@xxxxxxxxx>
---
 mm/page_alloc.c |    9 +++++++++
 1 file changed, 9 insertions(+)

Index: linux/mm/page_alloc.c
===================================================================
--- linux.orig/mm/page_alloc.c	2009-07-10 11:36:07.000000000 +0800
+++ linux/mm/page_alloc.c	2009-07-13 09:25:21.000000000 +0800
@@ -475,6 +475,15 @@ static inline void __free_one_page(struc
 		order++;
 	}
 	set_page_order(page, order);
+
+	if (order >= pageblock_order && migratetype != MIGRATE_MOVABLE) {
+		int i;
+
+		migratetype = MIGRATE_MOVABLE;
+		for (i = 0; i < (1 << (order - pageblock_order)); i++)
+			set_pageblock_migratetype(page +
+				i * pageblock_nr_pages, MIGRATE_MOVABLE);
+	}
 	list_add(&page->lru,
 		&zone->free_area[order].free_list[migratetype]);
 	zone->free_area[order].nr_free++;
--
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