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SubjectRe: [PATCH 6/6] memcg: fix performance of mem_cgroup_begin_update_page_stat()
On Fri, Feb 17, 2012 at 06:28:51PM +0900, KAMEZAWA Hiroyuki wrote:
> >From 07d3ce332ee4bc1eaef4b8fb2019b0c06bd7afb1 Mon Sep 17 00:00:00 2001
> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> Date: Mon, 6 Feb 2012 12:14:47 +0900
> Subject: [PATCH 6/6] memcg: fix performance of mem_cgroup_begin_update_page_stat()
>
> mem_cgroup_begin_update_page_stat() should be very fast because
> it's called very frequently. Now, it needs to look up page_cgroup
> and its memcg....this is slow.
>
> This patch adds a global variable to check "any memcg is moving or not".
> With this, the caller doesn't need to visit page_cgroup and memcg.
>
> Here is a test result. A test program makes page faults onto a file,
> MAP_SHARED and makes each page's page_mapcount(page) > 1, and free
> the range by madvise() and page fault again. This program causes
> 26214400 times of page fault onto a file(size was 1G.) and shows
> shows the cost of mem_cgroup_begin_update_page_stat().
>
> Before this patch for mem_cgroup_begin_update_page_stat()
> [kamezawa@bluextal test]$ time ./mmap 1G
>
> real 0m21.765s
> user 0m5.999s
> sys 0m15.434s
>
> 27.46% mmap mmap [.] reader
> 21.15% mmap [kernel.kallsyms] [k] page_fault
> 9.17% mmap [kernel.kallsyms] [k] filemap_fault
> 2.96% mmap [kernel.kallsyms] [k] __do_fault
> 2.83% mmap [kernel.kallsyms] [k] __mem_cgroup_begin_update_page_stat
>
> After this patch
> [root@bluextal test]# time ./mmap 1G
>
> real 0m21.373s
> user 0m6.113s
> sys 0m15.016s
>
> In usual path, calls to __mem_cgroup_begin_update_page_stat() goes away.
>
> Note: we may be able to remove this optimization in future if
> we can get pointer to memcg directly from struct page.
>
> Acked-by: Greg Thelen <gthelen@google.com>
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

Acked-by: Johannes Weiner <hannes@cmpxchg.org>


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