Re: [PATCH 0/6] power_of_2 emulation support for NVMe ZNS devices

Luis Chamberlain
2022-03-11T22:24:13Z

On Fri, Mar 11, 2022 at 01:31:02PM -0800, Keith Busch wrote:
> On Fri, Mar 11, 2022 at 01:04:35PM -0800, Luis Chamberlain wrote:
> > On Fri, Mar 11, 2022 at 12:51:35PM -0800, Keith Busch wrote:
> >
> > > I'm starting to like the previous idea of creating an unholey
> > > device-mapper for such users...
> >
> > Won't that restrict nvme with chunk size crap. For instance later if we
> > want much larger block sizes.
>
> I'm not sure I understand. The chunk_size has nothing to do with the
> block size. And while nvme is a user of this in some circumstances, it
> can't be used concurrently with ZNS because the block layer appropriates
> the field for the zone size.

Many device mapper targets split I/O into chunks, see max_io_len(),
wouldn't this create an overhead?

Using a device mapper target also creates a divergence in strategy
for ZNS. Some will use the block device, others the dm target. The
goal should be to create a unified path.

And all this, just because SMR. Is that worth it? Are we sure?

Luis