From: Greg Banks <gnb@melbourne.sgi.com>
Subject: Re: Different NFSSVC_MAXBLKSIZE for udp and tcp clients?
Date: Thu, 27 Nov 2003 12:33:50 +1100
Sender: nfs-admin@lists.sourceforge.net
Message-ID: <3FC5547E.7EBF817@melbourne.sgi.com>
References: <3FC3929C.EFFE5CDF@moving-picture.com>
		<3FC3FD0C.B2DD2183@melbourne.sgi.com>
		<3FC483D6.6753DCA3@moving-picture.com>
		<16325.9710.935587.140271@notabene.cse.unsw.edu.au>
		<3FC54373.EC448BB1@melbourne.sgi.com> <16325.18142.376089.406722@notabene.cse.unsw.edu.au>
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Cc: James Pearson <james-p@moving-picture.com>,
   Trond Myklebust <trond.myklebust@fys.uio.no>, nfs@lists.sourceforge.net
To: Neil Brown <neilb@cse.unsw.edu.au>
Errors-To: nfs-admin@lists.sourceforge.net

Neil Brown wrote:
> 
> On Thursday November 27, gnb@melbourne.sgi.com wrote:
> > Neil Brown wrote:
> >
> > The point is that the server's maximum is too low, [...]
> 
> Why didn't you say so then (or did you and I missed it?).

Sorry, just being obscure ;-)

> The code in 2.4 is not ready to cope well with larger NFS packets. [...]
> For a 32k write, that means a
> kmalloc(32768) has to succeed, and very often free memory is too
> fragmented for it to succeed.
> 
> For tcp, the request will be copied into a pre-allocated buffer.  The
> (large) buffer is allocated when the nfsd thread is started,[...]

Ok, so if physical memory fragmentation is the only issue I'll just
try it.  With 16K pages the allocation orders will be more reasonable.

> 2.6 copes with page-lists and so can handle requests and replies that
> are not cntiguous in memory, so this is not an issue and MAXBLKSIZE
> can safely be increased.

Excellent, this sounds like it deals with my long-term issue.

> I suggest that you simply recompile the kernel with a larger
> NFSSVC_MAXBLKSIZE and see how well it works.
> I can see no reasonable for having different values for udp and tcp
> though.  Just make it uniformly 32768 and see how it goes.

How about I conditionally define NFSSVC_MAXBLKSIZE to 32k if the
page size is sufficently large?  Would such a patch make it into 2.4?

Greg.
-- 
Greg Banks, R&D Software Engineer, SGI Australian Software Group.
I don't speak for SGI.


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