Re: [PATCH RFC] fsio: filesystem io accounting cgroup

[Konstantin Khlebnikov <khlebnikov@openvz.org>]

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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