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In-Reply-To: <20091119132828.29aba7b2.nishimura@mxp.nes.nec.co.jp>
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	 <20091119132828.29aba7b2.nishimura@mxp.nes.nec.co.jp>
Date: Thu, 19 Nov 2009 13:42:19 -0800
Message-ID: <6599ad830911191342q3709338apc14950a6de80b128@mail.gmail.com>
Subject: Re: [PATCH -mmotm 1/5] cgroup: introduce cancel_attach()
From: Paul Menage <menage@google.com>
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Sender: owner-linux-mm@kvack.org
To: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: linux-mm <linux-mm@kvack.org>, Andrew Morton <akpm@linux-foundation.org>, Balbir Singh <balbir@linux.vnet.ibm.com>, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>, Li Zefan <lizf@cn.fujitsu.com>
List-ID: <linux-mm.kvack.org>

On Wed, Nov 18, 2009 at 8:28 PM, Daisuke Nishimura
<nishimura@mxp.nes.nec.co.jp> wrote:
> This patch adds cancel_attach() operation to struct cgroup_subsys.
> cancel_attach() can be used when can_attach() operation prepares somethin=
g
> for the subsys, but we should rollback what can_attach() operation has pr=
epared
> if attach task fails after we've succeeded in can_attach().
>
> Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
> Acked-by: Li Zefan <lizf@cn.fujitsu.com>

Reviewed-by: Paul Menage <menage@google.com>

> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 /*
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0* Rememb=
er at which subsystem we've failed in
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0* can_at=
tach() to call cancel_attach() only
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0* agains=
t subsystems whose attach() have
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0* succee=
ded(see below).

Maybe: Remember on which subsystem the can_attach() failed, so that we
only call cancel_attach() against the subsystems whose can_attach()
succeeded. (See below)

> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 /*
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0* This m=
eans can_attach() of this subsystem
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0* have f=
ailed, so we don't need to call
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0* cancel=
_attach() against rests of subsystems.
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0*/

Maybe: This subsystem was the one that failed the can_attach() check
earlier, so we don't need to call cancel_attach() against it or any
remaining subsystems.

Paul

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