linux-kernel - [PATCH 13/24] mm, page_alloc: Remove redundant check for empty zonelist

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Message-Id: <1460455945-29644-14-git-send-email-mgorman@techsingularity.net>
Date:	Tue, 12 Apr 2016 11:12:14 +0100
From:	Mel Gorman <mgorman@...hsingularity.net>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Vlastimil Babka <vbabka@...e.cz>, Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Mel Gorman <mgorman@...hsingularity.net>
Subject: [PATCH 13/24] mm, page_alloc: Remove redundant check for empty zonelist

A check is made for an empty zonelist early in the page allocator fast
path but it's unnecessary. The check after first_zones_zonelist call
should catch that situation. Removing the first check is slower for
machines with memoryless nodes but that is a corner case that can
live with the overhead.

Signed-off-by: Mel Gorman <mgorman@...hsingularity.net>
---
 mm/page_alloc.c | 8 --------
 1 file changed, 8 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index df03ccc7f07c..e50e754ec9eb 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3374,14 +3374,6 @@ __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int order,
 	if (should_fail_alloc_page(gfp_mask, order))
 		return NULL;
 
-	/*
-	 * Check the zones suitable for the gfp_mask contain at least one
-	 * valid zone. It's possible to have an empty zonelist as a result
-	 * of __GFP_THISNODE and a memoryless node
-	 */
-	if (unlikely(!zonelist->_zonerefs->zone))
-		return NULL;
-
 	if (IS_ENABLED(CONFIG_CMA) && ac.migratetype == MIGRATE_MOVABLE)
 		alloc_flags |= ALLOC_CMA;
 
-- 
2.6.4