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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