[PATCH] memcg: do not recalculate section unnecessarily ininit_section_page_cgroup

[Fernando Luis Vázquez Cao]

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@xxxxxxxxxxxxx>
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
---

diff -urNp linux-2.6.28-rc2-mm1-orig/mm/page_cgroup.c linux-2.6.28-rc2-mm1/mm/page_cgroup.c
--- linux-2.6.28-rc2-mm1-orig/mm/page_cgroup.c	2008-10-30 12:49:27.000000000 +0900
+++ linux-2.6.28-rc2-mm1/mm/page_cgroup.c	2008-10-30 12:52:41.000000000 +0900
@@ -99,13 +99,11 @@ struct page_cgroup *lookup_page_cgroup(s
 
 int __meminit 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)
 		return 0;
 
@@ -131,7 +129,6 @@ int __meminit init_section_page_cgroup(u
 		__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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