From: Matthew Wilcox <willy@infradead.org>
To: Neal Gompa <ngompa13@gmail.com>
Cc: jack@suse.cz, linux-nvdimm@lists.01.org, darrick.wong@oracle.com,
david@fromorbit.com, linux-kernel@vger.kernel.org,
Shiyang Ruan <ruansy.fnst@fujitsu.com>,
linux-xfs@vger.kernel.org, ocfs2-devel@oss.oracle.com,
viro@zeniv.linux.org.uk,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
dan.j.williams@intel.com,
Btrfs BTRFS <linux-btrfs@vger.kernel.org>
Subject: Re: [Ocfs2-devel] [PATCH v2 00/10] fsdax, xfs: Add reflink&dedupe support for fsdax
Date: Wed, 10 Mar 2021 13:55:31 +0000 [thread overview]
Message-ID: <20210310135531.GP3479805@casper.infradead.org> (raw)
In-Reply-To: <CAEg-Je-F6ybPPV22-hq9=cuUCA7cw2xAA7Y-97tKhYUX1+fDwg@mail.gmail.com>
On Wed, Mar 10, 2021 at 08:36:06AM -0500, Neal Gompa wrote:
> On Wed, Mar 10, 2021 at 8:02 AM Matthew Wilcox <willy@infradead.org> wrote:
> >
> > On Wed, Mar 10, 2021 at 07:30:41AM -0500, Neal Gompa wrote:
> > > Forgive my ignorance, but is there a reason why this isn't wired up to
> > > Btrfs at the same time? It seems weird to me that adding a feature
> >
> > btrfs doesn't support DAX. only ext2, ext4, XFS and FUSE have DAX support.
> >
> > If you think about it, btrfs and DAX are diametrically opposite things.
> > DAX is about giving raw access to the hardware. btrfs is about offering
> > extra value (RAID, checksums, ...), none of which can be done if the
> > filesystem isn't in the read/write path.
> >
> > That's why there's no DAX support in btrfs. If you want DAX, you have
> > to give up all the features you like in btrfs. So you may as well use
> > a different filesystem.
>
> So does that mean that DAX is incompatible with those filesystems when
> layered on DM (e.g. through LVM)?
Yes. It might be possible to work through RAID-0 or read-only through
RAID-1, but I'm not sure anybody's bothered to do that work.
> Also, based on what you're saying, that means that DAX'd resources
> would not be able to use reflinks on XFS, right? That'd put it in
> similar territory as swap files on Btrfs, I would think.
You can use DAX with reflinks because the CPU can do read-only mmaps.
On a write fault, we break the reflink, copy the data and put in a
writable PTE.
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next prev parent reply other threads:[~2021-03-10 13:56 UTC|newest]
Thread overview: 73+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-26 0:20 [Ocfs2-devel] [PATCH v2 00/10] fsdax, xfs: Add reflink&dedupe support for fsdax Shiyang Ruan
2021-02-26 0:20 ` [Ocfs2-devel] [PATCH v2 01/10] fsdax: Factor helpers to simplify dax fault code Shiyang Ruan
2021-03-03 9:13 ` Christoph Hellwig
2021-02-26 0:20 ` [Ocfs2-devel] [PATCH v2 02/10] fsdax: Factor helper: dax_fault_actor() Shiyang Ruan
2021-03-03 9:28 ` Christoph Hellwig
2021-03-12 9:01 ` ruansy.fnst
2021-02-26 0:20 ` [Ocfs2-devel] [PATCH v2 03/10] fsdax: Output address in dax_iomap_pfn() and rename it Shiyang Ruan
2021-02-26 0:20 ` [Ocfs2-devel] [PATCH v2 05/10] fsdax: Replace mmap entry in case of CoW Shiyang Ruan
2021-03-03 9:30 ` Christoph Hellwig
2021-03-03 9:41 ` ruansy.fnst
2021-03-03 9:44 ` Christoph Hellwig
2021-03-03 9:48 ` Christoph Hellwig
2021-02-26 0:20 ` [Ocfs2-devel] [PATCH v2 08/10] fsdax: Dedup file range to use a compare function Shiyang Ruan
2021-02-26 8:28 ` Shiyang Ruan
2021-03-03 8:20 ` Joe Perches
2021-03-03 8:45 ` ruansy.fnst
2021-03-03 9:04 ` Joe Perches
2021-03-03 9:39 ` hch
2021-03-03 9:46 ` ruansy.fnst
2021-03-04 5:42 ` [Ocfs2-devel] [RESEND PATCH v2.1 " Shiyang Ruan
2021-02-26 0:20 ` [Ocfs2-devel] [PATCH v2 09/10] fs/xfs: Handle CoW for fsdax write() path Shiyang Ruan
2021-03-03 9:43 ` Christoph Hellwig
2021-03-03 9:57 ` ruansy.fnst
2021-03-03 10:43 ` Christoph Hellwig
2021-03-04 1:35 ` ruansy.fnst
2021-02-26 0:20 ` [Ocfs2-devel] [PATCH v2 10/10] fs/xfs: Add dedupe support for fsdax Shiyang Ruan
2021-02-26 9:45 ` [Ocfs2-devel] Question about the "EXPERIMENTAL" tag for dax in XFS ruansy.fnst
2021-02-26 19:04 ` Darrick J. Wong
2021-02-26 19:24 ` Dan Williams
2021-02-26 20:51 ` Dave Chinner
2021-02-26 20:59 ` Dan Williams
2021-02-26 21:27 ` Dave Chinner
2021-02-26 22:41 ` Dan Williams
2021-02-27 22:36 ` Dave Chinner
2021-02-27 23:40 ` Dan Williams
2021-02-28 22:38 ` Dave Chinner
2021-03-01 20:55 ` Dan Williams
2021-03-01 22:46 ` Dave Chinner
2021-03-02 0:32 ` Dan Williams
2021-03-02 2:42 ` Dave Chinner
2021-03-02 3:33 ` Dan Williams
2021-03-02 5:38 ` Dave Chinner
2021-03-02 5:50 ` Dan Williams
2021-03-02 3:28 ` Darrick J. Wong
2021-03-02 5:41 ` Dan Williams
2021-03-02 7:57 ` Dave Chinner
2021-03-02 17:49 ` Dan Williams
2021-03-04 23:40 ` Darrick J. Wong
2021-03-01 7:26 ` Yasunori Goto
2021-03-01 21:34 ` Dan Williams
[not found] ` <20210226002030.653855-5-ruansy.fnst@fujitsu.com>
2021-03-03 9:29 ` [Ocfs2-devel] [PATCH v2 04/10] fsdax: Introduce dax_iomap_cow_copy() Christoph Hellwig
[not found] ` <20210226002030.653855-7-ruansy.fnst@fujitsu.com>
2021-03-03 9:31 ` [Ocfs2-devel] [PATCH v2 06/10] fsdax: Add dax_iomap_cow_copy() for dax_iomap_zero Christoph Hellwig
[not found] ` <20210226002030.653855-8-ruansy.fnst@fujitsu.com>
2021-02-26 4:14 ` [Ocfs2-devel] [PATCH v2 07/10] iomap: Introduce iomap_apply2() for operations on two files Darrick J. Wong
2021-02-26 8:11 ` ruansy.fnst
2021-02-26 8:25 ` Shiyang Ruan
2021-03-04 5:41 ` [Ocfs2-devel] [RESEND PATCH v2.1 " Shiyang Ruan
2021-03-11 12:30 ` Christoph Hellwig
2021-03-09 6:36 ` [Ocfs2-devel] [PATCH v2 00/10] fsdax, xfs: Add reflink&dedupe support for fsdax Xiaoguang Wang
2021-03-10 1:32 ` ruansy.fnst
2021-03-09 16:19 ` Goldwyn Rodrigues
2021-03-10 1:26 ` ruansy.fnst
2021-03-10 12:30 ` Neal Gompa
2021-03-10 13:02 ` Matthew Wilcox
2021-03-10 13:36 ` Neal Gompa
2021-03-10 13:55 ` Matthew Wilcox [this message]
2021-03-10 14:21 ` Goldwyn Rodrigues
2021-03-10 14:26 ` Matthew Wilcox
2021-03-10 17:04 ` Goldwyn Rodrigues
2021-03-11 0:53 ` Dan Williams
2021-03-11 8:26 ` Neal Gompa
2021-03-13 13:07 ` Adam Borowski
2021-03-13 16:24 ` Neal Gompa
2021-03-13 22:00 ` Adam Borowski
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