Re: How does NILFS2 handle directory management

From: Jiro SEKIBA <jir-hfpbi5WX9J54Eiagz67IpQ@public.gmane.org>
To: NILFS Users mailing list <users-JrjvKiOkagjYtjvyW6yDsg@public.gmane.org>
Subject: Re: How does NILFS2 handle directory management
Date: Fri, 11 Sep 2009 12:48:37 +0900	[thread overview]
Message-ID: <873a6u16qy.wl%jir@sekiba.com> (raw)
In-Reply-To: <20090911.102118.69189169.ryusuke-sG5X7nlA6pw@public.gmane.org>

Hi

As far as I see, nilfs2 directory management is based on ext2.
ext3 has same format as ext2, but file creation is faster than ext2.
http://plaza18.mbn.or.jp/~moriban/linux/img/FileSystemBenchmarkResults-01-03.png
# There may be more reliable benchmark result, but I cound't find it.

So I think it would be worth to try porting ext3 code to nilfs2
to improve file creation.  Isn't it?

thanks,

regards,
-- 
Jiro SEKIBA <jir-hfpbi5WX9J54Eiagz67IpQ@public.gmane.org>

At Fri, 11 Sep 2009 10:21:18 +0900 (JST),
Ryusuke Konishi wrote:
> 
> Hi Prasenjit Giri, and Reinoud,
> On Thu, 10 Sep 2009 21:26:19 +0200, Reinoud Zandijk <wrote:
> > Hi Prasenjit Giri,
> > 
> > On Fri, Sep 11, 2009 at 12:46:04AM +0530, Prasenjit Giri wrote:
> > > Even after looking through various sites, forums, mailing lists I could not
> > > uncover the present directoy management of NILFS2.
> > > 
> > > As I see a B-tree directory management in your long term to do list, it
> > > would be really nice if someone would ought to share the information
> > > regarding the present directory management of NILFS2
> > 
> > Currently directories are recorded just as a sequential file but not filled
> > with user data but with dirent entries in their blocks like ext2fs does.
> > Nothing special about that :)
> >
> > I dont know if b+tree directory management would be preferable though. With
> > some smart caching all directory operations can be made O(1) anyway.
> > 
> > With regards,
> > Reinoud Zandijk
> 
> Yes, directory is a file and it's already managed with b-tree like
> other files.  However, the current directory design is not O(log n),
> and is actually slow especially for file creation.
> 
> So, it leaves room for considering the true "b-tree directory
> management".
> 
> OTOH, the replacement has the following points to notice:
> 
>  1) It may complicate the log writer.
> 
>     The current log writer is designed on the basis that every data
>     and meta data is a file.  In NILFS, inodes, segment usage state,
>     and checkpoints, are managed with correponding meta-data files.
> 
>     The true "b-tree directory management" may break this uniformity.
> 
>  2) A disk format change is required.
>     (We can deem this a trade-off at this stage)
> 
> This may be a -v3 material.  But anyway, patch proposals are welcome.
> 
> Thank you,
> Ryusuke Konishi
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> 