Re: [PATCH 6/7 v2] ext4: lookup block mapping in extent status tree

[Zheng Liu <gnehzuil.liu@gmail.com>]

On Thu, Jan 17, 2013 at 11:00:06PM -0500, Theodore Ts'o wrote:
> On Fri, Jan 11, 2013 at 06:53:46PM +0800, Zheng Liu wrote:
> > From: Zheng Liu <wenqing.lz@taobao.com>
> > 
> > After tracking all extent status, we already have a extent cache in memory.
> > Every time we want to lookup a block mapping, we can first try to lookup it in
> > extent status tree to avoid a potential disk I/O.
> > 
> > A new function called ext4_es_lookup_extent is defined to finish this work.
> > When we try to lookup a block mapping, we always call ext4_map_blocks and/or
> > ext4_da_map_blocks.  So in these functions we first try to lookup a block
> > mapping in extent status tree.
> > 
> > CC: Jan kara <jack@suse.cz>
> > CC: "Theodore Ts'o" <tytso@mit.edu>
> > Signed-off-by: Zheng Liu <wenqing.lz@taobao.com>
> 
> Once we apply this this patch, we should be able to remove the the
> single-entry extent cache in fs/ext4/extents.c ---
> ext4_ext_put_in_cache(), ext4_ext_put_gap_in_cache(),
> ext4_ext_in_cache() --- since the extent status tree makes this code
> redundant (and will do a better job).  This would be a good follow up,
> cleanup patch.

Fair enough.  The patch that tries to remove extent cache will be sent out
in next version.

Thanks,
                                                - Zheng