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>

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 49d40261f8c45545e927b80566d44f8f6c95303d..af65c4eedc79061522f0c858b9a5ec715daf2986 100644 (file)
--- 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);

diff --git a/mm/page_isolation.c b/mm/page_isolation.c
index dadb7e74d7d6b3d9b44dc57a6af1878f43c5bd3f..f4e17a57926afffa33fceabf81a742ffc254d914 100644 (file)
--- a/mm/page_isolation.c
+++ b/mm/page_isolation.c
@@ -106,7 +106,7 @@ static void unset_migratetype_isolate(struct page *page, unsigned migratetype)
                        buddy_pfn = __find_buddy_pfn(pfn, order);
                        buddy = page + (buddy_pfn - pfn);
 
-                       if (pfn_valid_within(page_to_pfn(buddy)) &&
+                       if (pfn_valid_within(buddy_pfn) &&
                            !is_migrate_isolate_page(buddy)) {
                                __isolate_free_page(page, order);
                                isolated_page = true;