linux-ext4 - Re: Questions about dx --- hash conflicts and limit

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Message-Id: <ADFAE24A-7440-4AA3-B74E-F8431D6C0F26@whamcloud.com>
Date:	Tue, 31 Jul 2012 11:56:49 -0700
From:	Andreas Dilger <adilger@...mcloud.com>
To:	Wang Sheng-Hui <shhuiw@...il.com>
Cc:	ext4 development <linux-ext4@...r.kernel.org>
Subject: Re: Questions about dx --- hash conflicts and limit

On 2012-07-31, at 6:12, Wang Sheng-Hui <shhuiw@...il.com> wrote:
> 
> I have 2 questions about dx in ext4:
> 
> 1) hash conflict
> 
>   I walked through the ext4/namei.c, but didn't find any
>   code dealing with hash conflicts.
> 
>   I wonder if some name hash conflicts, how can they be stored
>   and retrieved with the dir ops?

Sorry, don't have code available to look at to comment on this issue. 

> 2) limit on size of dir
> 
>   For the limit on items of the dir, the dir size is limited
>   to a height of 2 HTree: 
>       root node
>          |
>    intermidate node ...
>        |    |
>    leaf node...
> 
>   Is this right?

Correct, though this is only an implementation limit and not a format limit.

We have a patch to increase the htree depth to 3 levels and beyond 2GB directories, but it needs e2fsck support still, and it needs to be separated from a patch that also allows multi-threaded access to the same directory (though not via the VFS, unfortunately).

You can find this patch in the Lustre Git repo at git.whamcloud.com/fs/lustre-release in the ldiskfs/patches directory, if you are interested in this. 

Cheers, Andreas--
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