linux-kernel - Re: [PATCH -V14 0/11] Generic name to handle and open by handle syscalls

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Date:	Wed, 7 Jul 2010 17:49:50 -0600
From:	Andreas Dilger <andreas.dilger@...cle.com>
To:	Nick Piggin <npiggin@...e.de>
Cc:	"J. Bruce Fields" <bfields@...ldses.org>,
	"Aneesh Kumar K. V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Neil Brown <neilb@...e.de>,
	Christoph Hellwig <hch@...radead.org>,
	"viro@...iv.linux.org.uk Viro" <viro@...iv.linux.org.uk>,
	"corbet@....net Corbet" <corbet@....net>,
	"hooanon05@...oo.co.jp Okajima" <hooanon05@...oo.co.jp>,
	linux-fsdevel@...r.kernel.org,
	"sfrench@...ibm.com French" <sfrench@...ibm.com>,
	"philippe.deniel@....FR Deniel" <philippe.deniel@....FR>,
	"linux-kernel@...r.kernel.org Mailinglist" 
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -V14 0/11] Generic name to handle and open by handle syscalls

On 2010-07-07, at 12:05, Nick Piggin wrote:
> On Wed, Jul 07, 2010 at 11:02:47AM -0600, Andreas Dilger wrote:
>> I think you are assuming too much about the use of the file handle.  What I'm interested in is not a userspace file server, but rather a more efficient way to have 10000's to millions of clients to be able to open the same regular file, without having to do full path traversal for each one.
> 
> Really? What kind of clients? What sort of speedups do you hope to see?
> Path traversal can get vastly cheaper in both single threaded and parallel
> cases with my locking changes.

This is for Lustre clients, but really any kind of network filesystem is equally affected.  This isn't really an issue of the local dcache performance, but rather network latency for each component of the path traversal, and for a large number of clients the metadata server is the bottleneck for doing the traversal.

> It is not acceptable to work around fixable deficiencies in our critical
> infrastructure like path walking with hacks like this. If path walking
> is still much too expensive, that's another story...

Two different problems, I'm afraid.

Cheers, Andreas
--
Andreas Dilger
Lustre Technical Lead
Oracle Corporation Canada Inc.

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