linux-ext4 - Re: The meaning of data=ordered as it relates to delayed allocation

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Message-ID: <20090119144554.GJ9482@skywalker>
Date:	Mon, 19 Jan 2009 20:15:54 +0530
From:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:	Theodore Tso <tytso@....edu>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: The meaning of data=ordered as it relates to delayed allocation

On Mon, Jan 19, 2009 at 07:45:13AM -0500, Theodore Tso wrote:
> On Mon, Jan 19, 2009 at 10:13:45AM +0530, Aneesh Kumar K.V wrote:
> > > So I wonder if we should either:
> > > 
> > > (a) make data=ordered force block allocation and writeback --- which
> > >     should just be a matter of disabling the
> > >     redirty_page_for_writepage() code path in ext4_da_writepage()
> > 
> > We can't do that because we cannot do block allocation there. So we need
> > to redirty the page that have unmapped buffer_heads.
> 
> What is preventing us from doing block allocation from
> ext4_da_writepage()?
> 

The callback is called with page lock held and we can't start a journal
with page lock held.

-aneesh
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