linux-kernel - Re: [PATCH RFC] fsio: filesystem io accounting cgroup

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Date:	Tue, 09 Jul 2013 17:15:14 +0400
From:	Konstantin Khlebnikov <khlebnikov@...nvz.org>
To:	Tejun Heo <tj@...nel.org>
CC:	Vivek Goyal <vgoyal@...hat.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Michal Hocko <mhocko@...e.cz>,
	cgroups@...r.kernel.org, Andrew Morton <akpm@...ux-foundation.org>,
	Sha Zhengju <handai.szj@...il.com>, devel@...nvz.org,
	Jens Axboe <axboe@...nel.dk>
Subject: Re: [PATCH RFC] fsio: filesystem io accounting cgroup

Tejun Heo wrote:
> Hello,
>
> On Tue, Jul 09, 2013 at 12:28:15PM +0400, Konstantin Khlebnikov wrote:
>> Yep, blkio has plenty problems and flaws and I don't get how it's related
>> to vfs layer, dirty set control and non-disk or network backed filesystems.
>> Any problem can be fixed by introducing new abstract layer, except too many
>> abstraction levels. Cgroup is pluggable subsystem, blkio has it's own plugins
>> and it's build on top of io scheduler plugin. All this stuff always have worked
>
> What does that have to do with anything?
>
>> with block devices. Now you suggest to handle all filesystems in this stack.
>> I think binding them to unrealated cgroup is rough leveling violation.
>
> How is blkio unrelated to filesystems mounted on block devices?
> You're suggesting a duplicate solution which can't be complete.

blkio controls block devices. not filesystems or superblocks or bdi or pagecache.
It's all about block layer and nothing more. Am I right?

So, you want to link some completely unrelated subsystems like NFS into the block layer?

>
>> NFS cannot be controlled only by network throttlers because we
>> cannot slow down writeback process when it happens, we must slow
>> down tasks who generates dirty memory.
>
> That's exactly the same problem why blkio doesn't work for async IOs
> right now, so if you're interested in the area, please contribute to
> fixing that problem.
>
>> Plus it's close to impossible to separate several workloads if they
>> share one NFS sb.
>
> Again, the same problem with blkio.  We need separate pressure
> channels on bdi for each cgroup.
>
> Thanks.
>

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