Re: Does XFS support cgroup writeback limiting?

[Dave Chinner <david@fromorbit.com>]

On Mon, Nov 23, 2015 at 11:08:42PM +0100, Lutz Vieweg wrote:
> 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?

Just make the same mods to XFS as the ext4 patch here:

http://www.spinics.net/lists/kernel/msg2014816.html

> 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...

Yes, I know, but no-one seems to care enough about it to provide
regression tests for it.

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com

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