linux-kernel - Re: [PATCH 04/15] brd: remove dax support

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Message-ID: <74de4b5f-eacd-9058-45e6-d7fcfb2f0d51@kernel.dk>
Date:   Sat, 4 Nov 2017 10:31:51 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Dan Williams <dan.j.williams@...el.com>, linux-nvdimm@...ts.01.org
Cc:     akpm@...ux-foundation.org, Matthew Wilcox <mawilcox@...rosoft.com>,
        linux-kernel@...r.kernel.org, linux-xfs@...r.kernel.org,
        linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
        Ross Zwisler <ross.zwisler@...ux.intel.com>, hch@....de
Subject: Re: [PATCH 04/15] brd: remove dax support

On 10/31/2017 05:21 PM, Dan Williams wrote:
> DAX support in brd is awkward because its backing page frames are
> distinct from the ones provided by pmem, dcssblk, or axonram. We need
> pfn_t_devmap() entries to fully support DAX, and the limited DAX support
> for pfn_t_special() page frames is not interesting for brd when pmem is
> already a superset of brd.  Lastly, brd is the only dax capable driver
> that may sleep in its ->direct_access() implementation. So it causes a
> global burden with no net gain of kernel functionality.
> 
> For all these reasons, remove DAX support.

Reviewed-by: Jens Axboe <axboe@...nel.dk>

-- 
Jens Axboe