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Date: Thu, 4 Jan 2018 09:16:29 +0100
From: Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH v4 01/18] mm, dax: introduce pfn_t_special()
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To: Dan Williams <dan.j.williams@intel.com>
Cc: jack@suse.cz, linux-nvdimm@lists.01.org, Benjamin Herrenschmidt <benh@kernel.crashing.org>, Heiko Carstens <heiko.carstens@de.ibm.com>, hch@lst.de, linux-xfs@vger.kernel.org, Martin Schwidefsky <schwidefsky@de.ibm.com>, Paul Mackerras <paulus@samba.org>, Michael Ellerman <mpe@ellerman.id.au>, linux-fsdevel@vger.kernel.org, akpm@linux-foundation.org
List-ID: <linux-nvdimm@lists.01.org>

On Sat, Dec 23, 2017 at 04:56:06PM -0800, Dan Williams wrote:
> In support of removing the VM_MIXEDMAP indication from DAX VMAs,
> introduce pfn_t_special() for drivers to indicate that _PAGE_SPECIAL
> should be used for DAX ptes. This also helps identify drivers like
> dccssblk that only want to use DAX in a read-only fashion without
> get_user_pages() support.
> 
> Ideally we could delete axonram and dcssblk DAX support, but if we need
> to keep it better make it explicit that axonram and dcssblk only support
> a sub-set of DAX due to missing _PAGE_DEVMAP support.

I'd suggest to just delete it for now.  If the powerpc and S/390
people have an interest in it they should resurrect it properly and
fully.
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