linux-kernel - Re: [PATCHSET] cgroup: cftype based file interface, take #2

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Date:	Sat, 31 Mar 2012 20:56:36 +0800
From:	Li Zefan <lizefan@...wei.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	glommer@...allels.com, lizf@...fujitsu.com,
	containers@...ts.linux-foundation.org, cgroups@...r.kernel.org,
	linux-kernel@...r.kernel.org, fweisbec@...il.com, rni@...gle.com,
	ctalbott@...gle.com
Subject: Re: [PATCHSET] cgroup: cftype based file interface, take #2

Tejun Heo wrote:

> Hey, Li.
> 
> On Fri, Mar 30, 2012 at 08:42:07PM +0800, Li Zefan wrote:
>>> This patch replaces cgroup file interface with cftype based one which
>>> allows dynamic additions and removals of cftype arrays whether the
>>> target subsystem is attached or not.  This can be used to make subsys
>>> rebinding via remount work properly but I intentionally avoided doing
>>> that at the moment.
>>
>> What's the problem with remount?
> 
> Subsys can't be changed if any non-root cgroup exists.
> 


Ah, this is a long-standing defect, which is documented in Doc/../cgroups.txt.
It's not trivial to fix it, and I never heard someone request it to be fixed.

>> and is it important enough that it should be fixed even the feature
>> is marked as deprecated?
> 
> I'm not sure.  We *might* need it during multi-mount -> single-mount
> transition depending on how that's implemented, so the "at the moment"
> qualifier.  It probably won't be fixed but I'm not fully sure.
> 


fine.

>>> This makes cgroup population simpler for controllers and will be used
>>> to allow controllers to be more dynamic.  e.g. blkio subsys has
>>> sub-policies which may come and go while blkio subsys is attached and
>>> it currently uses fixed set of files which stays blank if not in use.
>>
>> Dynamic cgroup files was mentioned before. The scenario in mind was blkio
>> control files can be added/removed automatically as devices come and ago.
>>
>> So this time blkio subsystem is really going to be made more dynamic
>> soon?
> 
> Patchset already posted.
> 
>   http://thread.gmane.org/gmane.linux.kernel.cgroups/1376
> 


Thanks!
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