Re: [PATCH 02/15] libnvdimm: infrastructure for btt devices

[Jeff Moyer]

Dan Williams <dan.j.williams@xxxxxxxxx> writes:

> On Mon, Jun 22, 2015 at 11:32 AM, Jeff Moyer <jmoyer@xxxxxxxxxx> wrote:
>> Christoph Hellwig <hch@xxxxxx> writes:
>>
>>> On Mon, Jun 22, 2015 at 09:48:03AM -0700, Dan Williams wrote:
>>>> Only if you abandon BTT on partitions, which at this point it seems
>>>> you're boldly committed to doing.  It's unacceptable to drop BTT on
>>>> the floor so I'll take a look at making BTT per-disk only for 4.2.
>>>
>>> If by partitions you mean block layer partitions: yes.  If by partitions
>>> you mean subdivision of nvdimms: no.
>>
>> How will this subdivision be recorded?  Not all NVDIMMs support the
>> label specification.
>
> ...and the ones that do only use labels for resolving aliasing, not
> partitioning.
>
>> Sysadmins are already familiar with partitions;  I'm not sure why we'd
>> deviate from that here.  What am I missing?
>
> I don't see the need to re-invent partitioning which is the path this
> requested rework is putting us on...
>
> However, when the need arises for smaller granularity BTT we can have
> the partition fight then.  To be clear, I believe that need is already
> here today, but I'm not in a position to push that agenda at this late
> date.

The xfs example is enough to convince me that we need to support btt on
a partition right now.  Otherwise, for RHEL at least, dax on xfs simply
won't be supported.

-Jeff
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