Re: Kyber scheduler brings system to halt when used on swap partition

[Omar Sandoval <osandov@osandov.com>]

On Thu, May 11, 2017 at 02:57:24PM +0200, Markus Trippelsdorf wrote:
> Using the new Kyber mq scheduler brings my system to a halt as soon as it
> starts swapping. The swap partition resides on an SSD and is the only
> partition in use on that drive.
> Symptoms are stuttering sound and non moving mouse pointer. After a
> while the monitor switches off, because it gets no signal anymore.
> At which point only a hard reset will bring the system back.
> 
> "none" works fine.

Thanks for testing, I'm taking a look to see if there's anything special
about the swap path that would trigger this. In the meantime, if you
swapoff your swap partition and do some I/O on it, what happens? Here's
a first-order guess at a fio job you could run:

fio --group_reporting --filename=$partition \
	--name swapin --numjobs=8 --ioengine=sync --rw=randread \
	--name swapout --numjobs=4 --ioengine=libaio --iodepth=8 --rw=randwrite

Interesting to note is that wbt, which Kyber borrowed ideas from, treats
kswapd specially, allowing it to queue more I/O than other processes. I
wonder if we need to do the same in Kyber.