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From: "Darrick J. Wong" <djwong@kernel.org>
To: Shiyang Ruan <ruansy.fnst@fujitsu.com>
Cc: Christoph Hellwig <hch@lst.de>,
	linux-xfs@vger.kernel.org, dan.j.williams@intel.com,
	david@fromorbit.com, linux-fsdevel@vger.kernel.org,
	linux-kernel@vger.kernel.org, nvdimm@lists.linux.dev,
	rgoldwyn@suse.de, viro@zeniv.linux.org.uk, willy@infradead.org,
	Ritesh Harjani <riteshh@linux.ibm.com>
Subject: Re: [PATCH v9 5/8] fsdax: Add dax_iomap_cow_copy() for dax_iomap_zero
Date: Thu, 16 Sep 2021 15:55:44 -0700	[thread overview]
Message-ID: <20210916225544.GF34830@magnolia> (raw)
In-Reply-To: <9fb0c82f-b2ae-82e3-62df-f0a473ed6395@fujitsu.com>

On Thu, Sep 16, 2021 at 04:49:19PM +0800, Shiyang Ruan wrote:
> 
> 
> On 2021/9/16 14:16, Christoph Hellwig wrote:
> > On Wed, Sep 15, 2021 at 06:44:58PM +0800, Shiyang Ruan wrote:
> > > +	rc = dax_direct_access(iomap->dax_dev, pgoff, 1, &kaddr, NULL);
> > > +	if (rc < 0)
> > > +		goto out;
> > > +	memset(kaddr + offset, 0, size);
> > > +	if (srcmap->addr != IOMAP_HOLE && srcmap->addr != iomap->addr) {
> > 
> > Should we also check that ->dax_dev for iomap and srcmap are different
> > first to deal with case of file system with multiple devices?
> 
> I have not thought of this case.  Isn't it possible to CoW between different
> devices?

There's nothing in the iomap API that prevents a filesystem from doing
that, though there are no filesystems today that do such a thing.

That said, if btrfs ever joins the fold (and adds DAX support) then they
could totally COW to a different device.

--D

> 
> 
> --
> Thanks,
> Ruan
> 
> > 
> > Otherwise looks good:
> > 
> > Reviewed-by: Christoph Hellwig <hch@lst.de>
> > 
> 
> 

  reply	other threads:[~2021-09-16 22:55 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-15 10:44 [PATCH v9 0/8] fsdax,xfs: Add reflink&dedupe support for fsdax Shiyang Ruan
2021-09-15 10:44 ` [PATCH v9 1/8] fsdax: Output address in dax_iomap_pfn() and rename it Shiyang Ruan
2021-09-16  0:09   ` Darrick J. Wong
2021-09-16  1:36     ` Shiyang Ruan
2021-09-15 10:44 ` [PATCH v9 2/8] fsdax: Introduce dax_iomap_cow_copy() Shiyang Ruan
2021-09-15 10:44 ` [PATCH v9 3/8] fsdax: Replace mmap entry in case of CoW Shiyang Ruan
2021-09-16 14:51   ` kernel test robot
2021-09-15 10:44 ` [PATCH v9 4/8] fsdax: Convert dax_iomap_zero to iter model Shiyang Ruan
2021-09-16  0:11   ` Darrick J. Wong
2021-09-16  6:15   ` Christoph Hellwig
2021-09-15 10:44 ` [PATCH v9 5/8] fsdax: Add dax_iomap_cow_copy() for dax_iomap_zero Shiyang Ruan
2021-09-16  6:16   ` Christoph Hellwig
2021-09-16  8:49     ` Shiyang Ruan
2021-09-16 22:55       ` Darrick J. Wong [this message]
2021-09-15 10:44 ` [PATCH v9 6/8] fsdax: Dedup file range to use a compare function Shiyang Ruan
2021-09-16  6:17   ` Christoph Hellwig
2021-09-15 10:45 ` [PATCH v9 7/8] xfs: support CoW in fsdax mode Shiyang Ruan
2021-09-16  0:22   ` Darrick J. Wong
2021-09-16  6:32     ` Christoph Hellwig
2021-09-17 15:33       ` Darrick J. Wong
2021-09-21  8:14         ` Christoph Hellwig
2021-09-16  6:23   ` Christoph Hellwig
2021-09-16  8:51     ` Shiyang Ruan
2021-09-15 10:45 ` [PATCH v9 8/8] xfs: Add dax dedupe support Shiyang Ruan
2021-09-16  0:30   ` Darrick J. Wong
2021-09-16  4:01     ` Shiyang Ruan
2021-09-16  4:18       ` Darrick J. Wong

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