From: Christoph Hellwig <hch@lst.de>
To: "Darrick J. Wong" <darrick.wong@oracle.com>
Cc: Christoph Hellwig <hch@lst.de>,
Goldwyn Rodrigues <rgoldwyn@suse.de>,
linux-fsdevel@vger.kernel.org, linux-btrfs@vger.kernel.org,
david@fromorbit.com, riteshh@linux.ibm.com,
Goldwyn Rodrigues <rgoldwyn@suse.com>
Subject: Re: [PATCH 03/15] iomap: Read page from srcmap for IOMAP_COW
Date: Mon, 2 Sep 2019 19:13:18 +0200 [thread overview]
Message-ID: <20190902171318.GA7102@lst.de> (raw)
In-Reply-To: <20190902170109.GD568270@magnolia>
On Mon, Sep 02, 2019 at 10:01:09AM -0700, Darrick J. Wong wrote:
> On Mon, Sep 02, 2019 at 06:31:24PM +0200, Christoph Hellwig wrote:
> > On Sun, Sep 01, 2019 at 03:08:24PM -0500, Goldwyn Rodrigues wrote:
> >
> > > + iomap_assert(!(iomap->flags & IOMAP_F_BUFFER_HEAD));
> > > + iomap_assert(srcmap->type == IOMAP_HOLE || srcmap->addr > 0);
> >
> > 0 can be a valid address in various file systems, so I don't think we
> > can just exclude it. Then again COWing from a hole seems pointless,
> > doesn't it?
>
> XFS does that if you set a cowextsize hint and a speculative cow
> preallocation ends up covering a hole. Granted I don't think there's
> much point in reading from a COW fork extent to fill in an unaligned
> buffered write since it /should/ just end up zero-filling the pagecache
> regardless of fork... but I don't see much harm in doing that.
That assumes you'd set the iomap-level COW flag for anything that
writes to the COW fork in XFS. Which doesn't sound right to me - the
iomap-level indicates that we actually need to read some data, which
for a hole is rather pointless as you said.
next prev parent reply other threads:[~2019-09-02 17:13 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-01 20:08 [PATCH v3 0/15] Btrfs iomap Goldwyn Rodrigues
2019-09-01 20:08 ` [PATCH 01/15] iomap: Introduce CONFIG_FS_IOMAP_DEBUG Goldwyn Rodrigues
2019-09-01 20:50 ` Darrick J. Wong
2019-09-02 16:29 ` Christoph Hellwig
2019-09-02 17:09 ` Darrick J. Wong
2019-09-02 17:18 ` Christoph Hellwig
2019-09-03 15:06 ` Darrick J. Wong
2019-09-01 20:08 ` [PATCH 02/15] iomap: Use a IOMAP_COW/srcmap for a read-modify-write I/O Goldwyn Rodrigues
2019-09-02 16:31 ` Christoph Hellwig
2019-09-03 3:18 ` Darrick J. Wong
2019-09-03 14:12 ` Goldwyn Rodrigues
2019-09-03 14:05 ` Goldwyn Rodrigues
2019-09-03 14:56 ` Darrick J. Wong
2019-09-01 20:08 ` [PATCH 03/15] iomap: Read page from srcmap for IOMAP_COW Goldwyn Rodrigues
2019-09-02 16:31 ` Christoph Hellwig
2019-09-02 17:01 ` Darrick J. Wong
2019-09-02 17:13 ` Christoph Hellwig [this message]
2019-09-01 20:08 ` [PATCH 04/15] btrfs: Eliminate PagePrivate for btrfs data pages Goldwyn Rodrigues
2019-09-01 20:08 ` [PATCH 05/15] btrfs: Add a simple buffered iomap write Goldwyn Rodrigues
2019-09-01 20:08 ` [PATCH 06/15] btrfs: Add CoW in iomap based writes Goldwyn Rodrigues
2019-09-01 20:08 ` [PATCH 07/15] btrfs: remove buffered write code made unnecessary Goldwyn Rodrigues
2019-09-01 20:08 ` [PATCH 08/15] fs: Export generic_file_buffered_read() Goldwyn Rodrigues
2019-09-01 20:08 ` [PATCH 09/15] btrfs: basic direct read operation Goldwyn Rodrigues
2019-09-01 20:08 ` [PATCH 10/15] btrfs: Carve out btrfs_get_extent_map_write() out of btrfs_get_blocks_write() Goldwyn Rodrigues
2019-09-01 20:08 ` [PATCH 11/15] btrfs: Rename __endio_write_update_ordered() to btrfs_update_ordered_extent() Goldwyn Rodrigues
2019-09-01 20:08 ` [PATCH 12/15] iomap: use a function pointer for dio submits Goldwyn Rodrigues
2019-09-02 16:41 ` Christoph Hellwig
2019-09-01 20:08 ` [PATCH 13/15] btrfs: Use iomap_dio_rw for performing direct I/O writes Goldwyn Rodrigues
2019-09-01 20:08 ` [PATCH 14/15] btrfs: Remove btrfs_dio_data and __btrfs_direct_write Goldwyn Rodrigues
2019-09-01 20:08 ` [PATCH 15/15] btrfs: update inode size during bio completion Goldwyn Rodrigues
2019-09-02 16:43 ` [PATCH v3 0/15] Btrfs iomap Christoph Hellwig
2019-09-03 3:51 ` Shiyang Ruan
2019-09-03 4:29 ` Darrick J. Wong
2019-09-03 5:00 ` Shiyang Ruan
2019-09-03 6:21 ` Christoph Hellwig
2019-09-03 13:44 ` Goldwyn Rodrigues
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