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Date: Tue, 25 Jan 2011 08:07:44 +0100
From: Johannes Weiner <hannes@cmpxchg.org>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "nishimura@mxp.nes.nec.co.jp" <nishimura@mxp.nes.nec.co.jp>,
        "balbir@linux.vnet.ibm.com" <balbir@linux.vnet.ibm.com>,
        "akpm@linux-foundation.org" <akpm@linux-foundation.org>
Subject: Re: [PATCH 3/3] memcg: fix race at move_parent around
 compound_order()
Message-ID: <20110125070744.GB2217@cmpxchg.org>
References: <20110125145720.cd0cbe16.kamezawa.hiroyu@jp.fujitsu.com>
 <20110125150516.fb2f5e06.kamezawa.hiroyu@jp.fujitsu.com>
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On Tue, Jan 25, 2011 at 03:05:16PM +0900, KAMEZAWA Hiroyuki wrote:
> Based on 
> 2.6.38-rc2 + 
>  mm-memcontrolc-fix-uninitialized-variable-use-in-mem_cgroup_move_parent.patch
> ==
> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> 
> A fix up mem_cgroup_move_parent() which use compound_order() in
> asynchrnous manner. This compound_order() may return unknown value
> because we don't take lock. Use PageTransHuge() and HPAGE_SIZE instead of
> it.
> 
> Also clean up for mem_cgroup_move_parent(). 
>  - remove unnecessary initialization of local variable.
>  - rename charge_size -> page_size
>  - remove unnecessary (wrong) comment.
>  - added a comment about THP.
> 
> Changelog:
>  - fixed page size calculation for avoiding race.
> 
> Note:
>  Current design take compound_page_lock() in caller of move_account().
>  This should be revisited when we implement direct move_task of hugepage
>  without splitting.
> 
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

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