Re: How does NILFS2 handle directory management

[Ryusuke Konishi <ryusuke-sG5X7nlA6pw@public.gmane.org>]

On Fri, 11 Sep 2009 12:48:37 +0900, Jiro SEKIBA wrote:
> 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?

Yeah, it sounds nice.  The approach seems to be able to avoid both
problems I mentioned.

Thanks,
Ryusuke Konishi

> 
> 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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> > 
> > 
> > 
> 
> 
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