linux-kernel - [PATCH 01/17] mm: page_alloc: Do not update zlc unless the zlc is active

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Date:	Thu,  1 May 2014 09:44:32 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	Linux-MM <linux-mm@...ck.org>,
	Linux-FSDevel <linux-fsdevel@...r.kernel.org>
Cc:	Johannes Weiner <hannes@...xchg.org>,
	Vlastimil Babka <vbabka@...e.cz>, Jan Kara <jack@...e.cz>,
	Michal Hocko <mhocko@...e.cz>, Hugh Dickins <hughd@...gle.com>,
	Mel Gorman <mgorman@...e.de>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: [PATCH 01/17] mm: page_alloc: Do not update zlc unless the zlc is active

The zlc is used on NUMA machines to quickly skip over zones that are full.
However it is always updated, even for the first zone scanned when the
zlc might not even be active. As it's a write to a bitmap that potentially
bounces cache line it's deceptively expensive and most machines will not
care. Only update the zlc if it was active.

Signed-off-by: Mel Gorman <mgorman@...e.de>
---
 mm/page_alloc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 5dba293..f8b80c3 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2044,7 +2044,7 @@ try_this_zone:
 		if (page)
 			break;
 this_zone_full:
-		if (IS_ENABLED(CONFIG_NUMA))
+		if (IS_ENABLED(CONFIG_NUMA) && zlc_active)
 			zlc_mark_zone_full(zonelist, z);
 	}
 
-- 
1.8.4.5

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