linux-ext4 - merging of adjacent extents in the extent tree

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Message-ID: <AANLkTik65LJpjB0ByQcvdNFuFRdUc6ODwzRtczdxS8B=@mail.gmail.com>
Date:	Thu, 17 Feb 2011 13:57:26 +0200
From:	Amir Goldstein <amir73il@...il.com>
To:	Theodore Tso <tytso@....edu>
Cc:	Yongqiang Yang <xiaoqiangnk@...il.com>,
	Ext4 snapshots <ext4_dreamz_project@...glegroups.com>,
	Ext4 Developers List <linux-ext4@...r.kernel.org>
Subject: merging of adjacent extents in the extent tree

Hi Ted,

I noticed the following item on Ext4 TODO list:
* Improve merging of adjacent extents in the extent tree
  (i.e., both to the left and to the right)
** Investigate better code factorization in all of the places that
   manipulate the extent tree (ext4_get_blocks, fallocate, direct I/O,
   uninit-to-init conversion code)

I wanted to bring to your attention (and everybody else's),
the experimental work that Yongqiang has been doing in his
ext4-defrag branch:
https://github.com/YANGYongqiang/ext4-snapshots/blob/ext4-defrag/fs/dext4/extents.c#L3547

His work is related to my post on opportunistic de-fragmentation:
http://marc.info/?l=linux-ext4&m=128927606801750&w=2

Another related work on his queue, which involves manipulation of extent
tree, is the move-on-write implementation for extent mapped files.

Anyway, if you have any tips for Yongqiang, regarding better code
factorization or other opportunities in which extent merging can
take place, please share your insight with us.

Also, if there already is a parallel effort on the subject,
please let us know, so we can collaborate efforts.

Thanks,
Amir.
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