mm, page_alloc: don't convert pfn to idx when merging

In __free_one_page() we do the buddy merging arithmetics on "page/buddy
index", which is just the lower MAX_ORDER bits of pfn.  The operations
we do that affect the higher bits are bitwise AND and subtraction (in
that order), where the final result will be the same with the higher
bits left unmasked, as long as these bits are equal for both buddies -
which must be true by the definition of a buddy.

We can therefore use pfn's directly instead of "index" and skip the
zeroing of >MAX_ORDER bits.  This can help a bit by itself, although
compiler might be smart enough already.  It also helps the next patch to
avoid page_to_pfn() for memory hole checks.

Link: http://lkml.kernel.org/r/20161216120009.20064-1-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, 2 insertions, 2 deletions

diff --git a/mm/internal.h b/mm/internal.h
index 7aa2ea0a8623..bfad3b5d2665 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -133,9 +133,9 @@ struct alloc_context {
  * Assumption: *_mem_map is contiguous at least up to MAX_ORDER
  */
 static inline unsigned long
-__find_buddy_index(unsigned long page_idx, unsigned int order)
+__find_buddy_pfn(unsigned long page_pfn, unsigned int order)
 {
-	return page_idx ^ (1 << order);
+	return page_pfn ^ (1 << order);
 }
 
 extern struct page *__pageblock_pfn_to_page(unsigned long start_pfn,