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Re: [PATCH 4/4] fix biosize option

To: Christoph Hellwig <hch@xxxxxx>
Subject: Re: [PATCH 4/4] fix biosize option
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Thu, 24 Jul 2008 17:15:19 +1000
Cc: xfs@xxxxxxxxxxx
In-reply-to: <20080525190754.GD13372@xxxxxx>
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References: <20080525190754.GD13372@xxxxxx>
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On Sun, May 25, 2008 at 09:07:54PM +0200, Christoph Hellwig wrote:
> iosizelog shouldn't be the same as iosize but the logarithm of it.  Then
> again the current biosize option doesn't make much sense to me as it
> doesn't set the preferred I/O size as mentioned in the comment next to

That's a hold-over from irix - biosize set the basic chunk size the
cache used for mapping writes, so was effectively the size of write
to use to avoid RMW cycles as well as the unit of delayed
allocation. 

> it but rather the allocation size and thus is identical to the allocsize
> option (except for the missing logarithm).  It's also not documented in
> Documentation/filesystems/xfs.txt or the mount manpage.

So when it was first added (probably for compatibility) the
allocation part was noticed and not the rest. Maybe we should
hook it up to xfs_preferred_iosize() rather than allocation now
that it exists...

Apart from that, yes it should be the logarithm, so ACK for this
minor mod...

Cheers,

Dave.
-- 
Dave Chinner
david@xxxxxxxxxxxxx


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