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[Bug 822] xfs mapping behavior changed between .28 and .29

To: xfs-masters@xxxxxxxxxxx
Subject: [Bug 822] xfs mapping behavior changed between .28 and .29
From: bugzilla-daemon@xxxxxxxxxxx
Date: Mon, 11 May 2009 17:05:17 -0500
Auto-submitted: auto-generated
In-reply-to: <bug-822-113@xxxxxxxxxxxxxxxx/bugzilla/>
References: <bug-822-113@xxxxxxxxxxxxxxxx/bugzilla/>
http://oss.sgi.com/bugzilla/show_bug.cgi?id=822





--- Comment #4 from Eric Sandeen <sandeen-xfs@xxxxxxxxxxx>  2009-05-11 17:05:16 
CST ---
(In reply to comment #3)

> The file does not get closed between writes, hence the speculative
> allocation @ EOF is not truncated away in ->release(). If you were
> to do this as two separate invocations of xfs_io, I think you'll
> see data/hole/data. 

yep, you will.

> IMO, with disks the size they are these days filling small holes
> is much nicer behaviour (fewer, larger reads when reading the files),
> so I'd say XFS is now behaving as it was designed to do.
> 
> FWIW, the length of the speculative allocation is configurable by
> mount option (biosize, log value), and the default is "16" (i.e
> 64k). Hence I think you could turn this off if you really wanted
> to...

There may be some diabolical cases here where we are having a pretty bad ratio
of filled-holes-to-what-we-thought-was-sparse, I'll poke at it a bit more.

I didn't think xfs -used- to do this, but ... not sure.

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