On Wed, Oct 17, 2018 at 4:59 PM Bryan Gurney [off-list ref] wrote:

I feel strongly about the prevention of users running into errors
because of an incorrect scheduler default, because I encountered that
situation three times in my testing with zoned block devices. The
switch to SCSI_MQ would resolve that, since mq-deadline is the
default, but in my case, I was using Fedora 28, which disables
CONFIG_SCSI_MQ_DEFAULT (which is enabled in the 4.18 kernel), so my
default scheduler was cfq.

I think we should make a patch to the kernel that makes it
impossible (even from sysfs) to choose a non-zone aware
scheduler for these devices.

It's another topic than $SUBJECT patch though. I take this
into account in this version.

Yours,
Linus Walleij