linux-kernel - Re: [PATCH v2] d_ino considered harmful

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Date:	Thu, 17 Jun 2010 14:17:17 -0400
From:	David Dillow <dillowda@...l.gov>
To:	"J. R. Okajima" <hooanon05@...oo.co.jp>
Cc:	Valerie Aurora <vaurora@...hat.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Christoph Hellwig <hch@...radead.org>,
	Miklos Szeredi <miklos@...redi.hu>,
	Jan Blunck <jblunck@...e.de>,
	Jamie Lokier <jamie@...reable.org>,
	David Woodhouse <dwmw2@...radead.org>,
	Arnd Bergmann <arnd@...db.de>,
	Andreas Dilger <adilger@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH v2] d_ino considered harmful

On Thu, 2010-06-17 at 14:04 -0400, J. R. Okajima wrote:
> David Dillow:
> > For example, our main Lustre scratch space has over 285 million files in
> > it, and using find -inum takes over 72 hours to walk the tree using
> 	:::
> > Using ne2scan -- which uses libext2fs and combines the inode scan and
> > the name lookup -- takes over 48 hours to generate a list of candidate
> > files for the purge example. With an optimized inode scan and the custom
> 	:::
> 
> While I've never heard of ne2scan, I am interested in this simplified
> problem such as "find the pathname(s) from an inum in a huge fs."
> Is ne2scan essentially equivalent to "debugfs ncheck inum"?

Yes, except it does that for every live inode in the system. ne2scan is
extended for use on Lustre's backing store -- it parses the LOV object
map and displays the information -- so I'm not sure how usable it will
be on an plain ext{2,3,4} file system. It is based off of e2scan in the
Oracle (nee Sun) Lustre version of e2fsprogs, so that could be a
starting point for you.

-- 
Dave Dillow
National Center for Computational Science
Oak Ridge National Laboratory
(865) 241-6602 office


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