From: Stephen Bates <sbates@raithlin.com>
To: Dave Chinner <david@fromorbit.com>
Cc: Christoph Hellwig <hch@infradead.org>,
Dan Williams <dan.j.williams@intel.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-nvdimm@lists.01.org" <linux-nvdimm@ml01.01.org>,
linux-rdma@vger.kernel.org, linux-block@vger.kernel.org,
Linux MM <linux-mm@kvack.org>,
Ross Zwisler <ross.zwisler@linux.intel.com>,
Matthew Wilcox <willy@linux.intel.com>,
jgunthorpe@obsidianresearch.com, haggaie@mellanox.com,
Jens Axboe <axboe@fb.com>, Jonathan Corbet <corbet@lwn.net>,
jim.macdonald@everspin.com, sbates@raithin.com,
Logan Gunthorpe <logang@deltatee.com>,
David Woodhouse <dwmw2@infradead.org>,
"Raj, Ashok" <ashok.raj@intel.com>
Subject: Re: [PATCH 0/3] iopmem : A block device for PCIe memory
Date: Tue, 25 Oct 2016 05:50:43 -0600 [thread overview]
Message-ID: <20161025115043.GA14986@cgy1-donard.priv.deltatee.com> (raw)
In-Reply-To: <20161021111253.GQ14023@dastard>
Hi Dave and Christoph
On Fri, Oct 21, 2016 at 10:12:53PM +1100, Dave Chinner wrote:
> On Fri, Oct 21, 2016 at 02:57:14AM -0700, Christoph Hellwig wrote:
> > On Fri, Oct 21, 2016 at 10:22:39AM +1100, Dave Chinner wrote:
> > > You do realise that local filesystems can silently change the
> > > location of file data at any point in time, so there is no such
> > > thing as a "stable mapping" of file data to block device addresses
> > > in userspace?
> > >
> > > If you want remote access to the blocks owned and controlled by a
> > > filesystem, then you need to use a filesystem with a remote locking
> > > mechanism to allow co-ordinated, coherent access to the data in
> > > those blocks. Anything else is just asking for ongoing, unfixable
> > > filesystem corruption or data leakage problems (i.e. security
> > > issues).
> >
Dave are you saying that even for local mappings of files on a DAX
capable system it is possible for the mappings to move on you unless
the FS supports locking? Does that not mean DAX on such FS is
inherently broken?
> > And at least for XFS we have such a mechanism :) E.g. I have a
> > prototype of a pNFS layout that uses XFS+DAX to allow clients to do
> > RDMA directly to XFS files, with the same locking mechanism we use
> > for the current block and scsi layout in xfs_pnfs.c.
>
Thanks for fixing this issue on XFS Christoph! I assume this problem
continues to exist on the other DAX capable FS?
One more reason to consider a move to /dev/dax I guess ;-)...
Stephen
> Oh, that's good to know - pNFS over XFS was exactly what I was
> thinking of when I wrote my earlier reply. A few months ago someone
> else was trying to use file mappings in userspace for direct remote
> client access on fabric connected devices. I told them "pNFS on XFS
> and write an efficient transport for you hardware"....
>
> Now that I know we've got RDMA support for pNFS on XFS in the
> pipeline, I can just tell them "just write an rdma driver for your
> hardware" instead. :P
>
> Cheers,
>
> Dave.
> --
> Dave Chinner
> david@fromorbit.com
next prev parent reply other threads:[~2016-10-25 12:38 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-10-18 21:42 [PATCH 0/3] iopmem : A block device for PCIe memory Stephen Bates
2016-10-18 21:42 ` [PATCH 1/3] memremap.c : Add support for ZONE_DEVICE IO memory with struct pages Stephen Bates
2016-10-19 17:50 ` Dan Williams
2016-10-19 18:40 ` Stephen Bates
2016-10-19 20:01 ` Dan Williams
2016-10-25 11:54 ` Stephen Bates
2016-10-18 21:42 ` [PATCH 2/3] iopmem : Add a block device driver for PCIe attached IO memory Stephen Bates
2016-10-28 6:45 ` Christoph Hellwig
2016-10-28 19:22 ` Logan Gunthorpe
2016-10-18 21:42 ` [PATCH 3/3] iopmem : Add documentation for iopmem driver Stephen Bates
2016-10-28 6:46 ` Christoph Hellwig
2016-10-19 3:51 ` [PATCH 0/3] iopmem : A block device for PCIe memory Dan Williams
2016-10-19 18:48 ` Stephen Bates
2016-10-19 19:58 ` Dan Williams
2016-10-19 22:54 ` Stephen Bates
2016-10-20 23:22 ` Dave Chinner
2016-10-21 9:57 ` Christoph Hellwig
2016-10-21 11:12 ` Dave Chinner
2016-10-25 11:50 ` Stephen Bates [this message]
2016-10-25 21:19 ` Dave Chinner
2016-11-06 14:05 ` Stephen Bates
2016-10-27 10:22 ` Sagi Grimberg
2016-10-27 12:32 ` Christoph Hellwig
2016-10-26 8:24 ` Haggai Eran
2016-10-26 13:39 ` Dan Williams
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