linux-kernel - Re: [PATCH] cgroups: handle failure of cgroup_populate

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Message-ID: <20090525094704.GA5709@linux.vnet.ibm.com>
Date:	Mon, 25 May 2009 15:17:04 +0530
From:	Dhaval Giani <dhaval@...ux.vnet.ibm.com>
To:	Li Zefan <lizf@...fujitsu.com>
Cc:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Paul Menage <menage@...gle.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux Containers <containers@...ts.linux-foundation.org>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	libcg-devel@...ts.sourceforge.net
Subject: Re: [PATCH] cgroups: handle failure of cgroup_populate_dir() at
	mount/remount

On Mon, May 25, 2009 at 05:14:58PM +0800, Li Zefan wrote:
> Dhaval Giani wrote:
> > On Fri, May 22, 2009 at 05:34:21PM +0900, KAMEZAWA Hiroyuki wrote:
> >> On Fri, 22 May 2009 16:35:14 +0800
> >> Li Zefan <lizf@...fujitsu.com> wrote:
> >>
> >>> KAMEZAWA Hiroyuki wrote:
> >>>> On Fri, 22 May 2009 11:00:12 +0800
> >>>> Li Zefan <lizf@...fujitsu.com> wrote:
> >>>>
> >>>>> Now we have 'stat' file in both memory and cpuacct subsystems. If we
> >>>>> mount these 2 subsystems with option 'noprefix', the creation of 'stat'
> >>>>> file for cpuacct will fail, but without any notificatin to the user.
> >>>>>
> >>>>> With this patch, we fail the mount/remount in this case.
> >>>>>
> >>>> Hm, shouldn't we allow "noprefix" to be effective only agaisnt cpuset ?
> >>>> I think it's just for backward-compatibility of cpuset.
> >>>> (I don't like the option at all.)
> >>>>
> >>> Yes, this mount option was introduced for cpuset. But it has been here for
> >>> a long time and people may use it when mounting other cgroup subsystems,
> >>> then is it OK to change to restrict its use within cpuset only?
> >> Asking libcgroup people may be appropriate...added CC.
> > 
> > We just realized that we were not handling the noprefix usage in
> 
> I guess handling noprefix will increase complexity of libcgroup? since we
> can't figure out which subsystem the file belongs to by looking at the
> prefix of the file.
> 

Yes, but that should be handled with the next set of features planned
for the library.

> > libcgroup. From the pov of the library, the option should either not
> > exist for any subsystem or for all of them. Anything else would mean
> > having to add special cases.
> > 
> 
> I don't see how to totally remove 'noprefix' while keep the backward 
> compatibility of cpuset, so I think we have to reserve it, and fix
> name collision caused by this option.

I agree with you.

-- 
regards,
Dhaval
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