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

From: Li Zefan
Date: Sat Mar 31 2012 - 08:57:25 EST

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.


>>> 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.

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