mm, page_alloc: avoid page_to_pfn() when merging buddies

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().

Link: http://lkml.kernel.org/r/20161216120009.20064-2-vbabka@suse.cz
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 5 insertions, 5 deletions

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 49d40261f8c4..af65c4eedc79 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 @@ continue_merging:
         while (order < max_order - 1) {
                 buddy_pfn = __find_buddy_pfn(pfn, order);
                 buddy = page + (buddy_pfn - pfn);
+
+                if (!pfn_valid_within(buddy_pfn))
+                        goto done_merging;
                 if (!page_is_buddy(page, buddy, order))
                         goto done_merging;
                 /*
@@ -862,7 +862,7 @@ done_merging:
          * 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 & pfn;
                 higher_page = page + (combined_pfn - pfn);