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

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Message-ID: <20130118040006.GB13785@thunk.org>
Date:	Thu, 17 Jan 2013 23:00:06 -0500
From:	Theodore Ts'o <tytso@....edu>
To:	Zheng Liu <gnehzuil.liu@...il.com>
Cc:	linux-ext4@...r.kernel.org, Jan kara <jack@...e.cz>,
	Zheng Liu <wenqing.lz@...bao.com>
Subject: Re: [PATCH 6/7 v2] ext4: lookup block mapping in extent status tree

On Fri, Jan 11, 2013 at 06:53:46PM +0800, Zheng Liu wrote:
> From: Zheng Liu <wenqing.lz@...bao.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@...e.cz>
> CC: "Theodore Ts'o" <tytso@....edu>
> Signed-off-by: Zheng Liu <wenqing.lz@...bao.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.

	       	       	 	- Ted
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