linux-kernel - Re: [RFC][PATCH 00/11] blkiocg async support

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Date:	Thu, 15 Jul 2010 09:00:48 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	Nauman Rafique <nauman@...gle.com>,
	Munehiro Ikeda <m-ikeda@...jp.nec.com>,
	linux-kernel@...r.kernel.org, Ryo Tsuruta <ryov@...inux.co.jp>,
	taka@...inux.co.jp, Andrea Righi <righi.andrea@...il.com>,
	Gui Jianfeng <guijianfeng@...fujitsu.com>,
	akpm@...ux-foundation.org, balbir@...ux.vnet.ibm.com
Subject: Re: [RFC][PATCH 00/11] blkiocg async support

On Wed, 14 Jul 2010 10:29:19 -0400
Vivek Goyal <vgoyal@...hat.com> wrote:
> > 
> > Cgroup's feature as mounting several subsystems at a mount point at once
> > is very useful in many case.
> 
> I agree that it is useful but if some controllers are not supporting
> hierarchy, it just adds to more confusion. And later when hierarchy
> support comes in, there will be additional issue of keeping this file
> "use_hierarchy" like memory controller.
> 
> So at this point of time , I am not too inclined towards allowing hierarchical
> cgroup creation but treating them as flat in CFQ. I think it adds to the
> confusion and user space should handle this situation.
> 

Hmm. 

Could you fix error code in create blkio cgroup ? It returns -EINVAL now.
IIUC, mkdir(2) doesn't return -EINVAL as error code (from man.)
Then, it's very confusing. I think -EPERM or -ENOMEM will be much better.

Anyway, I need to see source code of blk-cgroup.c to know why libvirt fails
to create cgroup. Where is the user-visible information (in RHEL or Fedora)
about "you can't use blkio-cgroup via libvirt or libcgroup" ?

Thanks,
-Kame

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