[RFC PATCH v3 10/35] mm: Use the correct migratetype during buddymerging

[Srivatsa S. Bhat]

While merging buddy free pages of a given order to make a higher order page,
the buddy allocator might coalesce pages belonging to *two* *different*
migratetypes of that order!

So, don't assume that both the buddies come from the same freelist;
instead, explicitly find out the migratetype info of the buddy page and use
it while merging the buddies.

Also, set the freepage migratetype of the buddy to the new one.

Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@xxxxxxxxxxxxxxxxxx>
---

 mm/page_alloc.c |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index b4b1275..07ac019 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -681,10 +681,14 @@ static inline void __free_one_page(struct page *page,
 			__mod_zone_freepage_state(zone, 1 << order,
 						  migratetype);
 		} else {
+			int mt;
+
 			area = &zone->free_area[order];
-			del_from_freelist(buddy, &area->free_list[migratetype]);
+			mt = get_freepage_migratetype(buddy);
+			del_from_freelist(buddy, &area->free_list[mt]);
 			area->nr_free--;
 			rmv_page_order(buddy);
+			set_freepage_migratetype(buddy, migratetype);
 		}
 		combined_idx = buddy_idx & page_idx;
 		page = page + (combined_idx - page_idx);

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