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

[Adam Manzanares <a.manzanares@samsung.com>]

On Fri, Mar 11, 2022 at 12:51:35PM -0800, Keith Busch wrote:
> On Fri, Mar 11, 2022 at 12:19:38PM -0800, Luis Chamberlain wrote:
> > NAND has no PO2 requirement. The emulation effort was only done to help
> > add support for !PO2 devices because there is no alternative. If we
> > however are ready instead to go down the avenue of removing those
> > restrictions well let's go there then instead. If that's not even
> > something we are willing to consider I'd really like folks who stand
> > behind the PO2 requirement to stick their necks out and clearly say that
> > their hw/fw teams are happy to deal with this requirement forever on ZNS.
> 
> Regardless of the merits of the current OS requirement, it's a trivial
> matter for firmware to round up their reported zone size to the next
> power of 2. This does not create a significant burden on their part, as
> far as I know.

I can't comment on FW burdens but adding po2 zone size creates holes for the 
FW to deal with as well.

> 
> And po2 does not even seem to be the real problem here. The holes seem
> to be what's causing a concern, which you have even without po2 zones.
> I'm starting to like the previous idea of creating an unholey
> device-mapper for such users...

I see holes as being caused by having to make zone size po2 when capacity is 
not po2. po2 should be tied to the holes, unless I am missing something. BTW if
we go down the dm route can we start calling it dm-unholy.