Re: NVMe ZNS last zone size

[Stefan Hajnoczi <stefanha@gmail.com>]

On Wed, 23 Aug 2023 at 14:53, Klaus Jensen <k.jensen@samsung.com> wrote:
>
> On Aug 23 22:58, Sam Li wrote:
> > Stefan Hajnoczi <stefanha@gmail.com> 于2023年8月23日周三 22:41写道：
> > >
> > > On Wed, 23 Aug 2023 at 10:24, Sam Li <faithilikerun@gmail.com> wrote:
> > > >
> > > > Hi Stefan,
> > > >
> > > > Stefan Hajnoczi <stefanha@gmail.com> 于2023年8月23日周三 21:26写道：
> > > > >
> > > > > Hi Sam and Klaus,
> > > > > Val is adding nvme-io_uring ZNS support to libblkio
> > > > > (https://gitlab.com/libblkio/libblkio/-/merge_requests/221) and asked
> > > > > how to test the size of the last zone when the namespace's total size
> > > > > is not a multiple of the zone size.
> > > >
> > > > I think a zone report operation can do the trick. Given zone configs,
> > > > the size of last zone should be [size - (nr_zones - 1) * zone_size].
> > > > Reporting last zone on such devices tells whether the value is
> > > > correct.
> > >
> > > In nvme_ns_zoned_check_calc_geometry() the number of zones is rounded down:
> > >
> > >   ns->num_zones = le64_to_cpu(ns->id_ns.nsze) / ns->zone_size;
> > >
> > > Afterwards nsze is recalculated as follows:
> > >
> > >   ns->id_ns.nsze = cpu_to_le64(ns->num_zones * ns->zone_size);
> > >
> > > I interpret this to mean that when the namespace's total size is not a
> > > multiple of the zone size, then the last part will be ignored and not
> > > exposed as a zone.
> >
> > I see. Current ZNS emulation does not support this case.
> >
>
> NVMe Zoned Namespaces requires all zones to be the same size. The
> "trailing zone" is a thing in SMR HDDs.

Thanks for letting me know.

Stefan