linux-ext4 - Re: Use fsck to free the space used by dir?

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Message-ID: <501CA44D.2010201@gmail.com>
Date:	Sat, 04 Aug 2012 12:25:49 +0800
From:	Wang Sheng-Hui <shhuiw@...il.com>
To:	Theodore Ts'o <tytso@....edu>
CC:	Eric Sandeen <sandeen@...hat.com>,
	ext4 development <linux-ext4@...r.kernel.org>
Subject: Re: Use fsck to free the space used by dir?

On 2012年08月04日 01:57, Theodore Ts'o wrote:
> On Fri, Aug 03, 2012 at 10:18:57AM -0500, Eric Sandeen wrote:
>> On 8/3/12 9:19 AM, Wang Sheng-Hui wrote:
>>> Dear all,
>>>
>>> I read through the namei.c code recently, but didn't notice any code to
>>> reduce the size of a dir file (append can increase its size though).
>>
>> Right, AFAIK nothing in kernelspace will reduce the size.
> 
> In theory, if the dir_index (htree) support is enabled, it would be
> possible for the kernel to reorganize the directory dynamically.  
> 
> If dir_index is not enabled, reorganizing the directory would would
> break any open readdir() sessions and any NFS server file handles.
> (Which means if the file system has been exported by NFS in the past,
> and expects to be exported by NFS in the future, reorg'ing a directory
> will seriously confuse any clients which have cached NFS handles.)
> 
> For that reason, historically we've never bothered to try to implement
> ways of decreasing the size of a directory --- especially since in
> most cases, sysadmins can do something like:
> 
> mkdir foo.new ; mv foo/* foo.new ; mv foo.new foo
> 
> which while isn't perfect, works most of the time.
> 
> Regards,
> 
> 						- Ted

Thanks for your patient explanations, Eric & Ted!

Regards,
Wang Sheng-Hui 
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