Re: [PATCH] Fix ext2 error reporting on fsync

[Jan Kara <jack@suse.cz>]

> 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):
> 
> - private_list can become `struct buffer_head *metadata_buffers'
  Ack.

> - 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.
  Umm, I'm not sure about this locking change. As I see the code,
private_lock is used for serializing several players accessing the
mapping (__find_get_block_slow, try_to_free_buffers, fsync_buffers_list,
mark_buffer_dirty_inode, __set_page_dirty_buffers,
invalidate_inode_buffer, remove_inode_buffers, grow_dev_page,
create_empty_buffers, bforget). So I'm now a bit lost which of the
private_locks belong to the mapping of the block device and which to the
mappings of the inodes. Or should all those use device's mapping's
private_lock and you indend to convert all those users to metadata_lock?

								Honza
-- 
Jan Kara <jack@suse.cz>
SuSE CR Labs