From 0753b0ef3b301895234fed02bea2c099c7ff4feb Mon Sep 17 00:00:00 2001
From: Fernando Luis Vazquez Cao <fernando@oss.ntt.co.jp>
Date: Wed, 7 Jan 2009 18:07:51 -0800
Subject: memcg: do not recalculate section unnecessarily in
 init_section_page_cgroup

In init_section_page_cgroup() the section a given pfn belongs to is
calculated at the top of the function and, despite the fact that the
pfn/section correspondence does not change, it is recalculated further
down the same function.  By computing this just once and reusing that
value we save some bytes in the object file and do not waste CPU cycles.

Signed-off-by: Fernando Luis Vazquez Cao <fernando@oss.ntt.co.jp>
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: Balbir Singh <balbir@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
 mm/page_cgroup.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

(limited to 'mm')

diff --git a/mm/page_cgroup.c b/mm/page_cgroup.c
index d6507a660ed6..df1e54a5ed19 100644
--- a/mm/page_cgroup.c
+++ b/mm/page_cgroup.c
@@ -103,13 +103,11 @@ struct page_cgroup *lookup_page_cgroup(struct page *page)
 /* __alloc_bootmem...() is protected by !slab_available() */
 static int __init_refok init_section_page_cgroup(unsigned long pfn)
 {
-	struct mem_section *section;
+	struct mem_section *section = __pfn_to_section(pfn);
 	struct page_cgroup *base, *pc;
 	unsigned long table_size;
 	int nid, index;
 
-	section = __pfn_to_section(pfn);
-
 	if (!section->page_cgroup) {
 		nid = page_to_nid(pfn_to_page(pfn));
 		table_size = sizeof(struct page_cgroup) * PAGES_PER_SECTION;
@@ -145,7 +143,6 @@ static int __init_refok init_section_page_cgroup(unsigned long pfn)
 		__init_page_cgroup(pc, pfn + index);
 	}
 
-	section = __pfn_to_section(pfn);
 	section->page_cgroup = base - pfn;
 	total_usage += table_size;
 	return 0;
-- 
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