linux-kernel - [PATCH 10/22] Remove a branch by assuming __GFP_HIGH == ALLOC

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Date:	Wed, 22 Apr 2009 14:53:15 +0100
From:	Mel Gorman <mel@....ul.ie>
To:	Mel Gorman <mel@....ul.ie>,
	Linux Memory Management List <linux-mm@...ck.org>
Cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Nick Piggin <npiggin@...e.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Lin Ming <ming.m.lin@...el.com>,
	Zhang Yanmin <yanmin_zhang@...ux.intel.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: [PATCH 10/22] 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@...ux-foundation.org: Suggested the hack]
Signed-off-by: Mel Gorman <mel@....ul.ie>
Reviewed-by: Pekka Enberg <penberg@...helsinki.fi>
Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
---
 mm/page_alloc.c |    6 ++++--
 1 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 0d23795..4f9cdaa 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1619,14 +1619,16 @@ 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;
-- 
1.5.6.5

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