Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [PATCH 04/15] brd: remove dax support
To:     Dan Williams <dan.j.williams@intel.com>, linux-nvdimm@lists.01.org
Cc:     akpm@linux-foundation.org, Matthew Wilcox <mawilcox@microsoft.com>,
        linux-kernel@vger.kernel.org, linux-xfs@vger.kernel.org,
        linux-mm@kvack.org, linux-fsdevel@vger.kernel.org,
        Ross Zwisler <ross.zwisler@linux.intel.com>, hch@lst.de
References: <150949209290.24061.6283157778959640151.stgit@dwillia2-desk3.amr.corp.intel.com>
 <150949211688.24061.1197869674847507598.stgit@dwillia2-desk3.amr.corp.intel.com>
From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <74de4b5f-eacd-9058-45e6-d7fcfb2f0d51@kernel.dk>
Date:   Sat, 4 Nov 2017 10:31:51 -0600
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101
 Thunderbird/52.4.0
MIME-Version: 1.0
In-Reply-To: <150949211688.24061.1197869674847507598.stgit@dwillia2-desk3.amr.corp.intel.com>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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@kernel.dk>

-- 
Jens Axboe


From 1582986524400661613@xxx Thu Nov 02 20:13:11 +0000 2017
X-GM-THRID: 1582818041467251394
X-Gmail-Labels: Inbox,Category Forums,HistoricalUnread