On Wed, Oct 03, 2018 at 07:42:15AM +0000, Damien Le Moal wrote:

Of note also is that host-managed like sequential zone devices are also likely
to show up soon with the work being done in the NVMe standard on the new "Zoned
namespace" feature proposal. These devices will also require a scheduler like
mq-deadline guaranteeing per-zone in-order delivery of sequential write
requests. Looking only at the number of queues of the device is not enough to
choose the best (most reasonnable/appropriate) scheduler.

We actually have a plan to avoid the need for a non-reordering scheduler
there (including a Linux prototype for it).  Lets see if it survives the
committee.