linux-kernel - [PATCH 06/22] Move check for disabled anti-fragmentation out of fastpath

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Date:	Wed, 22 Apr 2009 14:53:11 +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 06/22] Move check for disabled anti-fragmentation out of fastpath

On low-memory systems, anti-fragmentation gets disabled as there is nothing
it can do and it would just incur overhead shuffling pages between lists
constantly. Currently the check is made in the free page fast path for every
page. This patch moves it to a slow path. On machines with low memory,
there will be small amount of additional overhead as pages get shuffled
between lists but it should quickly settle.

Signed-off-by: Mel Gorman <mel@....ul.ie>
Reviewed-by: Christoph Lameter <cl@...ux-foundation.org>
Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
---
 include/linux/mmzone.h |    3 ---
 mm/page_alloc.c        |    4 ++++
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 186ec6a..f82bdba 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -50,9 +50,6 @@ extern int page_group_by_mobility_disabled;
 
 static inline int get_pageblock_migratetype(struct page *page)
 {
-	if (unlikely(page_group_by_mobility_disabled))
-		return MIGRATE_UNMOVABLE;
-
 	return get_pageblock_flags_group(page, PB_migrate, PB_migrate_end);
 }
 
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 1e09f26..b1ae435 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -172,6 +172,10 @@ int page_group_by_mobility_disabled __read_mostly;
 
 static void set_pageblock_migratetype(struct page *page, int migratetype)
 {
+
+	if (unlikely(page_group_by_mobility_disabled))
+		migratetype = MIGRATE_UNMOVABLE;
+
 	set_pageblock_flags_group(page, (unsigned long)migratetype,
 					PB_migrate, PB_migrate_end);
 }
-- 
1.5.6.5

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