linux-ext4 - Re: [RFC] delayed allocation for ext4

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Date:	Sat, 23 Dec 2006 09:27:18 +0000
From:	Christoph Hellwig <hch@...radead.org>
To:	David Chinner <dgc@....com>
Cc:	Alex Tomas <alex@...sterfs.com>, linux-ext4@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC] delayed allocation for ext4

On Sat, Dec 23, 2006 at 02:31:23PM +1100, David Chinner wrote:
> >  - ext4-delayed-allocation.patch
> >    delayed allocation itself, enabled by "delalloc" mount option.
> >    extents support is also required. currently it works only
> >    with blocksize=pagesize.
> 
> Ah, that's why you can get away with a page flag - you've ignored
> the partial page delay state problem. Any plans to use the
> existing method in the future so we will be able to use ext4 delalloc
> on machines with a page size larger than 4k?

I think fixing this up for blocksize < pagesize is an absolute requirement
to get things merged.  We don't need more filesystems that are crippled
on half of our platforms.

Note that recording delayed alloc state at a page granularity in addition
to just the buffer heads has a lot of advantages aswell and would help
xfs, too.  But I think it makes a lot more sense to record it as a radix
tree tag to speed up the gang lookups for delalloc conversion.
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