linux-kernel - Re: [PATCH 3/3] memcg: fix race at move_parent around compound

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Message-ID: <20110125070744.GB2217@cmpxchg.org>
Date:	Tue, 25 Jan 2011 08:07:44 +0100
From:	Johannes Weiner <hannes@...xchg.org>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"nishimura@....nes.nec.co.jp" <nishimura@....nes.nec.co.jp>,
	"balbir@...ux.vnet.ibm.com" <balbir@...ux.vnet.ibm.com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>
Subject: Re: [PATCH 3/3] memcg: fix race at move_parent around
 compound_order()

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@...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@...fujitsu.com>

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