linux-ext4 - Re: [patch 0/9] writeback data integrity and other fixes (take 3)

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Message-ID: <20081029052707.GH4985@disturbed>
Date:	Wed, 29 Oct 2008 16:27:07 +1100
From:	Dave Chinner <david@...morbit.com>
To:	Nick Piggin <npiggin@...e.de>
Cc:	akpm@...ux-foundation.org, xfs@....sgi.com,
	linux-fsdevel@...r.kernel.org,
	Chris Mason <chris.mason@...cle.com>,
	linux-ext4@...r.kernel.org
Subject: Re: [patch 0/9] writeback data integrity and other fixes (take 3)

On Wed, Oct 29, 2008 at 05:00:14AM +0100, Nick Piggin wrote:
> On Wed, Oct 29, 2008 at 02:16:45PM +1100, Dave Chinner wrote:
> > FWIW, the core issue here is that we've got to do the
> > filemap_fdatawait() call in the ->fsync method because ->fsync
> > gets called before we've waited for the data I/O to complete.
> > XFS updates inode state on I/O completion, so we *must* wait
> > for data I/O to complete before logging the inode changes. I
> > think btrfs has the same problem....
> 
> Interesting. Does that mean you can do without the final filemap_fdatawait?

We could, yes.

> Can you do the first fdatawait without i_mutex held?

I don't see why not - I/O completion is only touching the XFS inode.
XFS has it's own inode locks for I/O and inode exclusion, and the
mapping tree lock protects the tree walk that the fdatawait is
doing...

> There was some talk IIRC about moving all this logic into the filesystem
> to provide more flexibility here. If there is still enough interest,
> we should get that moving...

It would simplify some of the code in XFS, that's for sure ;)

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
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