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

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Message-ID: <x49bng7v9v5.fsf@segfault.boston.devel.redhat.com>
Date:	Mon, 22 Jun 2015 15:09:02 -0400
From:	Jeff Moyer <jmoyer@...hat.com>
To:	Dan Williams <dan.j.williams@...el.com>
Cc:	Christoph Hellwig <hch@....de>, Jens Axboe <axboe@...nel.dk>,
	"linux-nvdimm\@lists.01.org" <linux-nvdimm@...1.01.org>,
	Neil Brown <neilb@...e.de>,
	Greg KH <gregkh@...uxfoundation.org>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Linux ACPI <linux-acpi@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH 02/15] libnvdimm: infrastructure for btt devices

Dan Williams <dan.j.williams@...el.com> writes:

> On Mon, Jun 22, 2015 at 11:32 AM, Jeff Moyer <jmoyer@...hat.com> wrote:
>> Christoph Hellwig <hch@....de> 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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