linux-ext4 - Re: Delayed allocation and page_lock vs transaction start ordering

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Message-ID: <20080416092614.GA6116@duck.suse.cz>
Date:	Wed, 16 Apr 2008 11:26:14 +0200
From:	Jan Kara <jack@...e.cz>
To:	Badari Pulavarty <pbadari@...il.com>
Cc:	linux-ext4@...r.kernel.org, sandeen@...hat.com
Subject: Re: Delayed allocation and page_lock vs transaction start ordering

On Tue 15-04-08 10:58:25, Badari Pulavarty wrote:
> 
> On Tue, 2008-04-15 at 18:14 +0200, Jan Kara wrote:
> > Hi,
> > 
> >   I've ported my patch inversing locking ordering of page_lock and
> > transaction start to ext4 (on top of ext4 patch queue). Everything except
> > delayed allocation is converted (the patch is below for interested
> > readers).
> 
> I am curious on the following code:
> 
> ext4_ordered_writepage()
> 
> + * Note that we don't need to start a transaction unless we're journaling
> + * data because we should have holes filled from ext4_page_mkwrite(). If
> + * we are journaling data, we cannot start transaction directly because
> + * transaction start ranks above page lock so we have to do some magic...
  Hmm, actually this comment becomes completely correct only after JBD
ordered mode rewrite patch ;). But the locking is correct even now - note
that we call block_write_full_page() before we start a transaction and
block_write_full_page() unlocks the page...

> Currently you are starting a transaction when the page is locked. 
> What do you plan to do here ?

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