linux-kernel - Re: [PATCH v5 0/7] fsdax,xfs: Add reflink&dedupe support for fsdax

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Date:   Mon, 10 May 2021 20:57:06 -0700
From:   "Darrick J. Wong" <djwong@...nel.org>
To:     Shiyang Ruan <ruansy.fnst@...itsu.com>
Cc:     linux-kernel@...r.kernel.org, linux-xfs@...r.kernel.org,
        linux-nvdimm@...ts.01.org, linux-fsdevel@...r.kernel.org,
        darrick.wong@...cle.com, dan.j.williams@...el.com,
        willy@...radead.org, viro@...iv.linux.org.uk, david@...morbit.com,
        hch@....de, rgoldwyn@...e.de
Subject: Re: [PATCH v5 0/7] fsdax,xfs: Add reflink&dedupe support for fsdax

On Tue, May 11, 2021 at 11:09:26AM +0800, Shiyang Ruan wrote:
> This patchset is attempt to add CoW support for fsdax, and take XFS,
> which has both reflink and fsdax feature, as an example.

Slightly off topic, but I noticed all my pmem disappeared once I rolled
forward to 5.13-rc1.  Am I the only lucky one?  Qemu 4.2, with fake
memory devices backed by tmpfs files -- info qtree says they're there,
but the kernel doesn't show anything in /proc/iomem.

--D

> Changes from V4:
>  - Fix the mistake of breaking dax layout for two inodes
>  - Add CONFIG_FS_DAX judgement for fsdax code in remap_range.c
>  - Fix other small problems and mistakes
> 
> Changes from V3:
>  - Take out the first 3 patches as a cleanup patchset[1], which has been
>     sent yesterday.
>  - Fix usage of code in dax_iomap_cow_copy()
>  - Add comments for macro definitions
>  - Fix other code style problems and mistakes
> 
> 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 mechanisms 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 v5.13-rc1 and patchset[1])
> [1]: https://lkml.org/lkml/2021/4/22/575
> 
> Shiyang Ruan (7):
>   fsdax: Introduce dax_iomap_cow_copy()
>   fsdax: Replace mmap entry in case of CoW
>   fsdax: Add dax_iomap_cow_copy() for dax_iomap_zero
>   iomap: Introduce iomap_apply2() for operations on two files
>   fsdax: Dedup file range to use a compare function
>   fs/xfs: Handle CoW for fsdax write() path
>   fs/xfs: Add dax dedupe support
> 
>  fs/dax.c               | 206 +++++++++++++++++++++++++++++++++++------
>  fs/iomap/apply.c       |  52 +++++++++++
>  fs/iomap/buffered-io.c |   2 +-
>  fs/remap_range.c       |  57 ++++++++++--
>  fs/xfs/xfs_bmap_util.c |   3 +-
>  fs/xfs/xfs_file.c      |  11 +--
>  fs/xfs/xfs_inode.c     |  66 ++++++++++++-
>  fs/xfs/xfs_inode.h     |   1 +
>  fs/xfs/xfs_iomap.c     |  61 +++++++++++-
>  fs/xfs/xfs_iomap.h     |   4 +
>  fs/xfs/xfs_iops.c      |   7 +-
>  fs/xfs/xfs_reflink.c   |  15 +--
>  include/linux/dax.h    |   7 +-
>  include/linux/fs.h     |  12 ++-
>  include/linux/iomap.h  |   7 +-
>  15 files changed, 449 insertions(+), 62 deletions(-)
> 
> -- 
> 2.31.1
> 
> 
>