linux-kernel - Re: [RFC][PATCH 1/6] memcg: fix pre

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Date:	Thu, 11 Dec 2008 09:25:31 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Paul Menage <menage@...gle.com>
Cc:	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"balbir@...ux.vnet.ibm.com" <balbir@...ux.vnet.ibm.com>,
	"nishimura@....nes.nec.co.jp" <nishimura@....nes.nec.co.jp>,
	"lizf@...fujitsu.com" <lizf@...fujitsu.com>,
	"kosaki.motohiro@...fujitsu.com" <kosaki.motohiro@...fujitsu.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCH 1/6] memcg: fix pre_destory handler

On Wed, 10 Dec 2008 10:35:34 -0800
Paul Menage <menage@...gle.com> wrote:

> On Wed, Dec 10, 2008 at 3:29 AM, KAMEZAWA Hiroyuki
> <kamezawa.hiroyu@...fujitsu.com> wrote:
> >
> > (BTW, I don't like hierarchy-walk-by-small-locks approarch now because
> >  I'd like to implement scan-and-stop-continue routine.
> >  See how readdir() aginst /proc scans PID. It's very roboust against
> >  very temporal PIDs.)
> 
> So you mean that you want to be able to sleep, and then contine
> approximately where you left off, without keeping any kind of
> reference count on the last cgroup that you touched? OK, so in that
> case I agree that you would need some kind of hierarch
> 
> > I tried similar patch and made it to use only one shared refcnt.
> > (my previous patch...)
> 
> A crucial difference is that your css_tryget() fails if the cgroups
> framework is trying to remove the cgroup but might abort due to
> another subsystem holding a reference, whereas mine spins and if the
> rmdir is aborted it will return a refcount.
> 
sure.
> >
> > We need rolling update of refcnts and rollback. Such code tends to make
> > a hole (This was what my first patch did...).
> 
> Can you clarify what you mean by "rolling update of refcnts"?
> 
 for(..i++)
	atomic_dec/inc( refcnt[i)

But my first version of this patch did above. I can write it again easily.

Thanks,
-Kame

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