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From: Dave Chinner <david@fromorbit.com>
To: Christoph Hellwig <hch@lst.de>
Cc: Goldwyn Rodrigues <rgoldwyn@suse.de>,
	linux-fsdevel@vger.kernel.org, linux-btrfs@vger.kernel.org,
	darrick.wong@oracle.com, linux-xfs@vger.kernel.org,
	Goldwyn Rodrigues <rgoldwyn@suse.com>
Subject: Re: [PATCH 15/15] xfs: Use the new iomap infrastructure for CoW
Date: Sat, 7 Sep 2019 09:28:12 +1000	[thread overview]
Message-ID: <20190906232812.GB16973@dread.disaster.area> (raw)
In-Reply-To: <20190906165507.GA12842@lst.de>

On Fri, Sep 06, 2019 at 06:55:07PM +0200, Christoph Hellwig wrote:
> On Thu, Sep 05, 2019 at 10:06:50AM -0500, Goldwyn Rodrigues wrote:
> > diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
> > index 8321733c16c3..13495d8a1ee2 100644
> > --- a/fs/xfs/xfs_iomap.c
> > +++ b/fs/xfs/xfs_iomap.c
> > @@ -1006,7 +1006,10 @@ xfs_file_iomap_begin(
> >  		 */
> >  		if (directio || imap.br_startblock == HOLESTARTBLOCK)
> >  			imap = cmap;
> > +		else
> > +			xfs_bmbt_to_iomap(ip, srcmap, &cmap, false);
> >  
> > +		iomap->flags |= IOMAP_F_COW;
> 
> I don't think this is correct.  We should only set IOMAP_F_COW
> when we actually fill out the srcmap.  Which is a very good agument
> for Darrick's suggestion to check for a non-emptry srcmap.
> 
> Also this is missing the actually interesting part in
> xfs_file_iomap_begin_delay.
> 
> I ended up spending the better half of the day trying to implement
> that and did run into a few bugs in the core iomap changes, mostly
> due to a confusion which iomap to use.  So I ended up reworking those
> a bit to:
> 
>   a) check srcmap->type to see if there is a valid srcmap
>   b) set the srcmap pointer to iomap so that it doesn't need to
>      be special cased all over
>   c) fixed up a few more places to use the srcmap
> 
> This now at least survives xfstests -g quick on a 4k xfs file system
> for.  Here is my current tree:
> 
> http://git.infradead.org/users/hch/xfs.git/shortlog/refs/heads/xfs-cow-iomap

That looks somewhat reasonable. The XFS mapping function is turning
into spagetti and getting really hard to follow again, though.
Perhaps we should consider splitting the shared/COW path out of
it...

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com

      reply	other threads:[~2019-09-06 23:28 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-09-05 15:06 [PATCH v4 0/15] CoW support for iomap Goldwyn Rodrigues
2019-09-05 15:06 ` [PATCH 01/15] iomap: Use a srcmap for a read-modify-write I/O Goldwyn Rodrigues
2019-09-05 23:23   ` Darrick J. Wong
2019-09-05 15:06 ` [PATCH 02/15] iomap: Read page from srcmap if IOMAP_F_COW is set Goldwyn Rodrigues
2019-09-05 16:37   ` Christoph Hellwig
2019-09-05 20:28     ` Goldwyn Rodrigues
2019-09-05 15:06 ` [PATCH 03/15] btrfs: Eliminate PagePrivate for btrfs data pages Goldwyn Rodrigues
2019-09-05 15:06 ` [PATCH 04/15] btrfs: Add a simple buffered iomap write Goldwyn Rodrigues
2019-09-05 16:23   ` Christoph Hellwig
2019-09-05 20:42     ` Goldwyn Rodrigues
2019-09-06  5:54       ` Christoph Hellwig
2019-09-05 15:06 ` [PATCH 05/15] btrfs: Add CoW in iomap based writes Goldwyn Rodrigues
2019-09-05 15:06 ` [PATCH 06/15] btrfs: remove buffered write code made unnecessary Goldwyn Rodrigues
2019-09-05 15:06 ` [PATCH 07/15] fs: Export generic_file_buffered_read() Goldwyn Rodrigues
2019-09-05 15:06 ` [PATCH 08/15] btrfs: basic direct read operation Goldwyn Rodrigues
2019-09-05 16:25   ` Christoph Hellwig
2019-09-05 15:06 ` [PATCH 09/15] btrfs: Carve out btrfs_get_extent_map_write() out of btrfs_get_blocks_write() Goldwyn Rodrigues
2019-09-05 15:06 ` [PATCH 10/15] btrfs: Rename __endio_write_update_ordered() to btrfs_update_ordered_extent() Goldwyn Rodrigues
2019-09-05 15:06 ` [PATCH 11/15] iomap: use a function pointer for dio submits Goldwyn Rodrigues
2019-09-05 16:27   ` Christoph Hellwig
2019-09-05 23:24     ` Darrick J. Wong
2019-09-05 15:06 ` [PATCH 12/15] btrfs: Use iomap_dio_rw for performing direct I/O writes Goldwyn Rodrigues
2019-09-05 16:31   ` Christoph Hellwig
2019-09-05 15:06 ` [PATCH 13/15] btrfs: Remove btrfs_dio_data and __btrfs_direct_write Goldwyn Rodrigues
2019-09-05 16:32   ` Christoph Hellwig
2019-09-05 15:06 ` [PATCH 14/15] btrfs: update inode size during bio completion Goldwyn Rodrigues
2019-09-05 16:33   ` Christoph Hellwig
2019-09-05 15:06 ` [PATCH 15/15] xfs: Use the new iomap infrastructure for CoW Goldwyn Rodrigues
2019-09-06 16:55   ` Christoph Hellwig
2019-09-06 23:28     ` Dave Chinner [this message]

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