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Date: Mon, 8 Nov 2010 09:07:35 +0900
Message-ID: <AANLkTinh+LEQYGe9dDOKBwNnVVXMiFYpDqkqvvpNe9H8@mail.gmail.com>
Subject: Re: [patch 4/4] memcg: use native word page statistics counters
From: Minchan Kim <minchan.kim@gmail.com>
To: Johannes Weiner <hannes@cmpxchg.org>
Cc: Greg Thelen <gthelen@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Dave Young <hidave.darkstar@gmail.com>,
        Andrea Righi <arighi@develer.com>,
        KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
        Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>,
        Balbir Singh <balbir@linux.vnet.ibm.com>,
        Wu Fengguang <fengguang.wu@intel.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
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On Mon, Nov 8, 2010 at 7:14 AM, Johannes Weiner <hannes@cmpxchg.org> wrote:
> The statistic counters are in units of pages, there is no reason to
> make them 64-bit wide on 32-bit machines.
>
> Make them native words. ?Since they are signed, this leaves 31 bit on
> 32-bit machines, which can represent roughly 8TB assuming a page size
> of 4k.
>
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
> ---
> ?include/linux/memcontrol.h | ? ?2 +-
> ?mm/memcontrol.c ? ? ? ? ? ?| ? 43 +++++++++++++++++++++----------------------
> ?mm/page-writeback.c ? ? ? ?| ? ?4 ++--
> ?3 files changed, 24 insertions(+), 25 deletions(-)
>

<snip>

>
> ?static unsigned long dirty_writeback_pages(void)
> ?{
> - ? ? ? s64 ret;
> + ? ? ? unsigned long ret;
>
> ? ? ? ?ret = mem_cgroup_page_stat(MEMCG_NR_DIRTY_WRITEBACK_PAGES);
> - ? ? ? if (ret < 0)
> + ? ? ? if ((long)ret < 0)
> ? ? ? ? ? ? ? ?ret = global_page_state(NR_UNSTABLE_NFS) +
> ? ? ? ? ? ? ? ? ? ? ? ?global_page_state(NR_WRITEBACK);

BTW, let me ask a question.
dirty_writeback_pages seems to be depends on mem_cgroup_page_stat's
result(ie, negative) for separate global and memcg.
But mem_cgroup_page_stat could return negative value by per-cpu as
well as root cgroup.
If I understand right, Isn't it a problem?

-- 
Kind regards,
Minchan Kim
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