linux-kernel - Re: [PATCH 2/2] cgroups: convert ss->attach to use whole threadgroup flex

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Message-ID: <20111014152218.GO14968@somewhere>
Date:	Fri, 14 Oct 2011 17:22:20 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Ben Blum <bblum@...rew.cmu.edu>
Cc:	Tejun Heo <tj@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>, linux-kernel@...r.kernel.org,
	NeilBrown <neilb@...e.de>, paulmck@...ux.vnet.ibm.com,
	Paul Menage <paul@...lmenage.org>,
	Li Zefan <lizf@...fujitsu.com>,
	containers@...ts.linux-foundation.org,
	Balbir Singh <bsingharora@...il.com>,
	Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [PATCH 2/2] cgroups: convert ss->attach to use whole threadgroup
 flex_array (cpuset, memcontrol)

On Fri, Oct 14, 2011 at 09:54:57AM -0400, Ben Blum wrote:
> On Fri, Oct 14, 2011 at 09:53:23AM -0400, Ben Blum wrote:
> > On Fri, Oct 14, 2011 at 02:21:30PM +0200, Frederic Weisbecker wrote:
> > > On Thu, Oct 13, 2011 at 08:36:01PM -0400, Ben Blum wrote:
> > > > Convert ss->attach to take a flex_array of tasks instead of just the leader.
> > > > 
> > > > From: Ben Blum <bblum@...rew.cmu.edu>
> > > > 
> > > > This lets subsystems with whole-threadgroup attach calls (i.e., cpuset and
> > > > memcontrol) to accurately find the group's mm even when a non-leader does exec
> > > > and leaves the leader with a NULL mm pointer.
> > > > 
> > > > Also converts cpuset and memcontrol to take the flex_array and iterate down it
> > > > until an mm is found, instead of just attempting to use the leader's mm.
> > > > 
> > > > Signed-off-by: Ben Blum <bblum@...rew.cmu.edu>
> > > 
> > > I think there are patches from Tejun that handle that did that already?
> > > 
> > > https://lkml.org/lkml/2011/8/23/418
> > > 
> > 
> > Yeah, I'm not hoping to preempt them or anything; I'm just presenting
> > this alternate approach, since (1) this way addresses the ss->attach()
> > problem directly without needing to add locking anywhere else, while the
> > focus of the discussion around Tejun's patches seems to have moved to
> > more global concerns, and (2) these patches and his patches ought to be
> > compatible with each other.
> 
> though, I did wonder if, given this approach, I shouldn't just get rid
> of attach_task and can_attach_task and use the flex_array for all of
> the calls. would that be nicer?

That's what Tejun's patches do.
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