[PATCH] mm/page_alloc: speeding up the iteration of max_order

[Muchun Song]

When we free a page whose order is very close to MAX_ORDER and greater
than pageblock_order, it wastes some CPU cycles to increase max_order
to MAX_ORDER one by one and check the pageblock migratetype of that page
repeatedly especially when MAX_ORDER is much larger than pageblock_order.

Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
---
 mm/page_alloc.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 141f12e5142c..959541234e1d 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1041,7 +1041,7 @@ static inline void __free_one_page(struct page *page,
 		pfn = combined_pfn;
 		order++;
 	}
-	if (max_order < MAX_ORDER) {
+	if (max_order < MAX_ORDER && order < MAX_ORDER - 1) {
 		/* If we are here, it means order is >= pageblock_order.
 		 * We want to prevent merge between freepages on isolate
 		 * pageblock and normal pageblock. Without this, pageblock
@@ -1062,6 +1062,8 @@ static inline void __free_one_page(struct page *page,
 						is_migrate_isolate(buddy_mt)))
 				goto done_merging;
 		}
+		if (unlikely(order != max_order - 1))
+			max_order = order + 1;
 		max_order++;
 		goto continue_merging;
 	}
-- 
2.11.0