linux-kernel - Re: [Lsf] [RFC] writeback and cgroup

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Date:	Wed, 4 Apr 2012 10:36:04 -0500
From:	Steve French <smfrench@...il.com>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	Tejun Heo <tj@...nel.org>, ctalbott@...gle.com, rni@...gle.com,
	andrea@...terlinux.com, containers@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org, lsf@...ts.linux-foundation.org,
	linux-mm@...ck.org, jmoyer@...hat.com, lizefan@...wei.com,
	linux-fsdevel@...r.kernel.org, cgroups@...r.kernel.org
Subject: Re: [Lsf] [RFC] writeback and cgroup

On Wed, Apr 4, 2012 at 9:51 AM, Vivek Goyal <vgoyal@...hat.com> wrote:
> On Tue, Apr 03, 2012 at 11:36:55AM -0700, Tejun Heo wrote:
>
> Hi Tejun,
>
> Thanks for the RFC and looking into this issue. Few thoughts inline.
>
> [..]
>> IIUC, without cgroup, the current writeback code works more or less
>> like this.  Throwing in cgroup doesn't really change the fundamental
>> design.  Instead of a single pipe going down, we just have multiple
>> pipes to the same device, each of which should be treated separately.
>> Of course, a spinning disk can't be divided that easily and their
>> performance characteristics will be inter-dependent, but the place to
>> solve that problem is where the problem is, the block layer.
>
> How do you take care of thorottling IO to NFS case in this model? Current
> throttling logic is tied to block device and in case of NFS, there is no
> block device.

Similarly smb2 gets congestion info (number of "credits") returned from
the server on every response - but not sure why congestion
control is tied to the block device when this would create
problems for network file systems

-- 
Thanks,

Steve
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