Re: Does XFS support cgroup writeback limiting?

[Lutz Vieweg <lvml@5t9.de>]

On 11/23/2015 09:26 PM, Dave Chinner wrote:
> On Mon, Nov 23, 2015 at 12:05:53PM +0100, Lutz Vieweg wrote:
>> in June 2015 the article https://lwn.net/Articles/648292/ mentioned
>> upcoming support for limiting the quantity of buffered writes
>> using control groups.
>>
>> Back then, only ext4 was said to support that feature, with other
>> filesystems requiring some minor changes to do the same.
>
> Yes, changing the kernel code to support this functionality is about
> 3 lines of code.

Oh, I didn't expect it to be such a small change :-)

> .... I haven't added support to XFS because I have no way of
> verifying the functionality works and that it continues to work as
> it is intended. i.e. we have no regression test coverage for cgroup
> aware writeback and until someone writes a set of regression tests
> that validate it's functionality works correctly it will remain this
> way.
>
> Writing code is trivial. Validating the code actually works as
> intended and doesn't silently get broken in the future is the
> hard part....

Understood, would you anyway be willing to publish such a
three-line-patch (outside of official releases) for those
daredevils (like me :-)) who'd be willing to give it a try?

After all, this functionality is the last piece of the
"isolation"-puzzle that is missing from Linux to actually
allow fencing off virtual machines or containers from DOSing
each other by using up all I/O bandwidth...

Regards,

Lutz Vieweg

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