page allocator: remove a branch by assuming __GFP_HIGH == ALLOC_HIGH

Allocations that specify __GFP_HIGH get the ALLOC_HIGH flag.  If these
flags are equal to each other, we can eliminate a branch.

[akpm@linux-foundation.org: Suggested the hack]
Signed-off-by: Mel Gorman <mel@csn.ul.ie>
Reviewed-by: Pekka Enberg <penberg@cs.helsinki.fi>
Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Christoph Lameter <cl@linux-foundation.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Dave Hansen <dave@linux.vnet.ibm.com>
Cc: Lee Schermerhorn <Lee.Schermerhorn@hp.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 4 insertions, 2 deletions

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index ef870fb92f74..94f33e2b7f0b 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1616,14 +1616,16 @@ gfp_to_alloc_flags(gfp_t gfp_mask)
         int alloc_flags = ALLOC_WMARK_MIN | ALLOC_CPUSET;
         const gfp_t wait = gfp_mask & __GFP_WAIT;
 
+        /* __GFP_HIGH is assumed to be the same as ALLOC_HIGH to save a branch. */
+        BUILD_BUG_ON(__GFP_HIGH != ALLOC_HIGH);
+
         /*
          * The caller may dip into page reserves a bit more if the caller
          * cannot run direct reclaim, or if the caller has realtime scheduling
          * policy or is asking for __GFP_HIGH memory.  GFP_ATOMIC requests will
          * set both ALLOC_HARDER (!wait) and ALLOC_HIGH (__GFP_HIGH).
          */
-        if (gfp_mask & __GFP_HIGH)
-                alloc_flags |= ALLOC_HIGH;
+        alloc_flags |= (gfp_mask & __GFP_HIGH);
 
         if (!wait) {
                 alloc_flags |= ALLOC_HARDER;