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From: Neal Gompa <ngompa13@gmail.com>
To: Shiyang Ruan <ruansy.fnst@fujitsu.com>
Cc: jack@suse.cz, darrick.wong@oracle.com, linux-nvdimm@lists.01.org,
	david@fromorbit.com, linux-kernel@vger.kernel.org,
	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 07:30:41 -0500	[thread overview]
Message-ID: <CAEg-Je-OLidbfzHCJvY55x+-cOfiUxX8CJ1AeN8VxXAVuVyxKQ@mail.gmail.com> (raw)
In-Reply-To: <20210226002030.653855-1-ruansy.fnst@fujitsu.com>

On Thu, Feb 25, 2021 at 7:23 PM Shiyang Ruan <ruansy.fnst@fujitsu.com> wrote:
>
> This patchset is attempt to add CoW support for fsdax, and take XFS,
> which has both reflink and fsdax feature, as an example.
>
> Changes from V1:
>  - Factor some helper functions to simplify dax fault code
>  - Introduce iomap_apply2() for dax_dedupe_file_range_compare()
>  - Fix mistakes and other problems
>  - Rebased on v5.11
>
> One of the key mechanism need to be implemented in fsdax is CoW.  Copy
> the data from srcmap before we actually write data to the destance
> iomap.  And we just copy range in which data won't be changed.
>
> Another mechanism is range comparison.  In page cache case, readpage()
> is used to load data on disk to page cache in order to be able to
> compare data.  In fsdax case, readpage() does not work.  So, we need
> another compare data with direct access support.
>
> With the two mechanism implemented in fsdax, we are able to make reflink
> and fsdax work together in XFS.
>
>
> Some of the patches are picked up from Goldwyn's patchset.  I made some
> changes to adapt to this patchset.
>
> (Rebased on v5.11)

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
like DAX to work with CoW filesystems is not being wired into *the*
CoW filesystem in the Linux kernel that fully takes advantage of
copy-on-write. I'm aware that XFS supports reflinks and does some
datacow stuff, but I don't know if I would consider XFS integration
sufficient for integrating this feature now, especially if it's
possible that the design might not work with Btrfs (I hadn't seen any
feedback from Btrfs developers, though given how much email there is
here, it's entirely possible that I missed it).


-- 
真実はいつも一つ!/ Always, there's only one truth!

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  parent reply	other threads:[~2021-03-11 18:38 UTC|newest]

Thread overview: 73+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-02-26  0:20 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 [this message]
2021-03-10 13:02   ` Matthew Wilcox
2021-03-10 13:36     ` Neal Gompa
2021-03-10 13:55       ` Matthew Wilcox
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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