[PATCH 2/2] mm, page_alloc: avoid page_to_pfn() when merging buddies

[Vlastimil Babka]

On architectures that allow memory holes, page_is_buddy() has to perform
page_to_pfn() to check for the memory hole. After the previous patch, we have
the pfn already available in __free_one_page(), which is the only caller of
page_is_buddy(), so move the check there and avoid page_to_pfn().

Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
---
 mm/page_alloc.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 812475bff8f3..6ba0782f7892 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -714,7 +714,7 @@ static inline void rmv_page_order(struct page *page)
 /*
  * This function checks whether a page is free && is the buddy
  * we can do coalesce a page and its buddy if
- * (a) the buddy is not in a hole &&
+ * (a) the buddy is not in a hole (check before calling!) &&
  * (b) the buddy is in the buddy system &&
  * (c) a page and its buddy have the same order &&
  * (d) a page and its buddy are in the same zone.
@@ -729,9 +729,6 @@ static inline void rmv_page_order(struct page *page)
 static inline int page_is_buddy(struct page *page, struct page *buddy,
 							unsigned int order)
 {
-	if (!pfn_valid_within(page_to_pfn(buddy)))
-		return 0;
-
 	if (page_is_guard(buddy) && page_order(buddy) == order) {
 		if (page_zone_id(page) != page_zone_id(buddy))
 			return 0;
@@ -808,6 +805,9 @@ static inline void __free_one_page(struct page *page,
 	while (order < max_order - 1) {
 		buddy_pfn = __find_buddy_pfn(page_pfn, order);
 		buddy = page + (buddy_pfn - page_pfn);
+
+		if (!pfn_valid_within(buddy_pfn))
+			goto done_merging;
 		if (!page_is_buddy(page, buddy, order))
 			goto done_merging;
 		/*
@@ -862,7 +862,7 @@ static inline void __free_one_page(struct page *page,
 	 * so it's less likely to be used soon and more likely to be merged
 	 * as a higher order page
 	 */
-	if ((order < MAX_ORDER-2) && pfn_valid_within(page_to_pfn(buddy))) {
+	if ((order < MAX_ORDER-2) && pfn_valid_within(buddy_pfn)) {
 		struct page *higher_page, *higher_buddy;
 		combined_pfn = buddy_pfn & page_pfn;
 		higher_page = page + (combined_pfn - page_pfn);
-- 
2.11.0