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

[Mingming Cao <cmm@us.ibm.com>]

On Mon, 2008-06-02 at 09:39 +0530, Aneesh Kumar K.V wrote:
> 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@us.ibm.com>
> > > > 
> > > > Need clear buffer_delay in ext4_da_writepage() after page has been writeout
> > > > 
> > > > Signed-off-by: Mingming Cao <cmm@us.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 buffer head passed to ext4_da_get_block_write() calling from
mpage_da_map_blocks is a dummy one, to store the allocated extent, not
the bh that need map.

>  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.
> 
It only clear the delayed bits if block_write_full_page() returns
successfully. But that reminds me to do some block reservation handling
for the error case.

> -aneesh
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