[PATCH] mm/page_alloc: find_large_buddy() from start_pfn aligned order

[Wei Yang <richard.weiyang@gmail.com>]

We iterate pfn from order 0 to MAX_PAGE_ORDER aligned to find large
buddy. While if the order is less than start_pfn aligned order, we would
get the same pfn and do the same check again.

Iterate from start_pfn aligned order to reduce duplicated work.

Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: David Hildenbrand <david@redhat.com>

---
I build this and run, but not sure how fully test this.
---
 mm/page_alloc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 27ea4c7acd15..7f2dfd30106f 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2033,7 +2033,7 @@ static int move_freepages_block(struct zone *zone, struct page *page,
 /* Look for a buddy that straddles start_pfn */
 static unsigned long find_large_buddy(unsigned long start_pfn)
 {
-	int order = 0;
+	int order = start_pfn ? __ffs(start_pfn) : MAX_PAGE_ORDER;
 	struct page *page;
 	unsigned long pfn = start_pfn;
 
-- 
2.34.1