linux-ext4 - Re: [PATCH] ext4: Need clear buffer_delay after page writeout for delayed allocation

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Message-ID: <20080602040934.GB17678@skywalker>
Date:	Mon, 2 Jun 2008 09:39:34 +0530
From:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:	Mingming Cao <cmm@...ibm.com>
Cc:	jack@...e.cz, linux-ext4@...r.kernel.org
Subject: Re: [PATCH] ext4: Need clear buffer_delay after page writeout for
	delayed allocation

On Sun, Jun 01, 2008 at 08:50:32PM -0700, Mingming Cao wrote:
> On Mon, 2008-06-02 at 08:44 +0530, Aneesh Kumar K.V wrote:
> > On Sun, Jun 01, 2008 at 02:10:02PM -0700, Mingming Cao wrote:
> > > ext4:  Need clear buffer_delay after page writeout for delayed allocation
> > > 
> > > From: Mingming Cao <cmm@...ibm.com>
> > > 
> > > Need clear buffer_delay in ext4_da_writepage() after page has been writeout
> > > 
> > > Signed-off-by: Mingming Cao <cmm@...ibm.com>
> > > 
> > > ---
> > 
> > We do that in mpage_put_bnr_to_bhs.
> > 
> Normally delayed buffer could be cleared in that case, but if allocation
> failed in __mapge_da_writepages(), it will keep buffer_delay marked and
> deferring to later ext4_da_writepage() to do block allocation. This
> patch handles clear bh delay bit in this case.
> 

Why not do it in ext4_da_get_block_write then. The reason being
block_write_full_page can return an error even though we have some of
the blocks allocated. With 1K block size we could allocate 3 blocks and 
fail for the last block in that case with the above patch we don't
clear the delay bit of the buffer head of all the blocks allocated.

-aneesh
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