From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andrew Morton <akpm@osdl.org>
Subject: Re: [PATCH] Fix ext2 error reporting on fsync
Date: Fri, 20 Jan 2006 13:33:20 -0800
Message-ID: <20060120133320.71bb0997.akpm@osdl.org>
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Andrew Morton <akpm@osdl.org> wrote:
>
> Andrew Morton <akpm@osdl.org> wrote:
> >
> >  Another approach would be to allocate a new buffer_head which "belongs" to
> >  the address_space.  So instead of doing:
> > 
> >  		bh<->bh<->address_space<->bh<->bh
> > 
> >  we do:
> > 
> >                       address_space
> >                             ^
> >                             |
> >                             v
> >  		bh<->bh<->bh'<->bh<->bh
> > 
> >  and set a magic bit in bh' which says "this is not a real bh; your
> >  address_space is at *b_private".
> 
> And if we do that, we can actually shrink the address_space by 2*sizeof(long):
> 

3*sizeof(long)!

> - private_list can become `struct buffer_head *metadata_buffers'
> 
> - and if we're going to abandon the address_space.private* genericity, we
>   can remove address_space.assoc_mapping and use a new
>   address_space->metadata_buffers->b_bdev->metadata_lock.

- nuke address_space.assoc_mapping, too.


Of course the cost is that written-to address_spaces will have an
associated extra bh.