linux-ext4 - Re: New ext4 patchset 2.6.26-rc8-ext4-1

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Message-ID: <20080708195353.GB22477@atrey.karlin.mff.cuni.cz>
Date:	Tue, 8 Jul 2008 21:53:53 +0200
From:	Jan Kara <jack@...e.cz>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Theodore Ts'o <tytso@....edu>, linux-ext4@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: New ext4 patchset 2.6.26-rc8-ext4-1

> On Sat, Jul 05, 2008 at 01:19:04PM -0400, Theodore Ts'o wrote:
> > Alex Tomas (2):
> >     * vfs: add basic delayed allocation support
> >     * ext4: Add basic delayed allocation support
> 
> Strong NACK.  For one thing the code added to mpage.c doesn't belong
> there.  It's far inferior to the existing delalloc code we already have
> and that could be made generic easily, or the next generation code
> developed by Chris mason.  It's an ext4-specific hack and doesn't belong
> into common code.  I'm pretty sure we agreed on not having it in
> common code long ago.
> 
> Also the code still deals with the !buffer_mapped and no buffers on page
> cases all over which isn't needed anymore with ->page_mkwrite implemented.
  I'd just comment on this: We've experimentally found out that page
without buffers *can* happen even with page_mkwrite() implementation.
  One path I remember we identified as possible cause is do_wp_page()
where buffers can be removed again from the page before it is marked
dirty. So if filesystem wants to be sure that buffers are really
attached to the page, I think it must mark the page (and through it buffers)
dirty before unlocking it...

> Similarly the !get_block case in mpage_da_writepages doesn't make any
> sense - it's never used and if people would want to use
> generic_writepages they could trivially just call it directly.

								Honza
-- 
Jan Kara <jack@...e.cz>
SuSE CR Labs
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