From mboxrd@z Thu Jan  1 00:00:00 1970
From: Peter Staubach <staubach@redhat.com>
Subject: Re: NFSv4/pNFS possible POSIX I/O API standards
Date: Tue, 05 Dec 2006 09:37:39 -0500
Message-ID: <45758433.9050704@redhat.com>
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Cc: Trond Myklebust <trond.myklebust@fys.uio.no>,
	Andreas Dilger <adilger@clusterfs.com>,
	Sage Weil <sage@newdream.net>,
	Christoph Hellwig <hch@infradead.org>,
	Brad Boyer <flar@allandria.com>,
	Anton Altaparmakov <aia21@cam.ac.uk>,
	Gary Grider <ggrider@lanl.gov>, linux-fsdevel@vger.kernel.org
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To: Rob Ross <rross@mcs.anl.gov>
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Rob Ross wrote:
>
> Regarding Peter Staubach's comments about no one ever using the 
> readdirplus() call; well, if people weren't performing this workload 
> in the first place, we wouldn't *need* this sort of call! This call is 
> specifically targeted at improving "ls -l" performance on large 
> directories, and Sage has pointed out quite nicely how that might work. 


I don't think that anyone has shown a *need* for this sort of call yet,
actually.  What application would actually benefit from this call and
where are the measurements?  Simply asserting that "ls -l" will benefit
is not enough without some measurements.  Or mention a different real
world application...

Having developed and prototyped the NFSv3 READDIRPLUS, I can tell you
that the wins were less than expected/hoped for and while it wasn't
all that hard to implement in a simple way, doing so in a high performance
fashion is much harder.  Many implementations that I have heard about
turn off READDIRPLUS when dealing with a large directory.

Caching is what makes things fast and caching means avoiding going
over the network.

       ps