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From: Daniel Phillips <phillips@bonn-fries.net>
To: Larry McVoy <lm@bitmover.com>
Subject: Re: SMP/cc Cluster description
Date: Thu, 6 Dec 2001 21:10:51 +0100
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Cc: Larry McVoy <lm@bitmover.com>, "David S. Miller" <davem@redhat.com>,
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On December 6, 2001 08:53 pm, Larry McVoy wrote:
> On Thu, Dec 06, 2001 at 08:42:05PM +0100, Daniel Phillips wrote:
> > On December 6, 2001 09:02 am, Larry McVoy wrote:
> > > On Wed, Dec 05, 2001 at 11:56:17PM -0800, David S. Miller wrote:
> > > > These lockless algorithms, instructions like CAS, DCAS, "infinite
> > > > consensus number", it's all crap.  You have to seperate out the access
> > > > areas amongst different cpus so they don't collide, and none of these
> > > > mechanisms do that.
> > > 
> > > Err, Dave, that's *exactly* the point of the ccCluster stuff.  You get
> > > all that seperation for every data structure for free.  Think about
> > > it a bit.  Aren't you going to feel a little bit stupid if you do all
> > > this work, one object at a time, and someone can come along and do the
> > > whole OS in one swoop?  Yeah, I'm spouting crap, it isn't that easy,
> > > but it is much easier than the route you are taking.  
> > 
> > What I don't get after looking at your material, is how you intend to do the 
> > locking.  Sharing a mmap across OS instances is fine, but how do processes on 
> > the two different OS's avoid stepping on each other when they access the same 
> > file?
> 
> Exactly the same way they would if they were two processes on a traditional
> SMP OS.

They'd use locks internal to the VFS and fs, plus Posix-style locks and
assorted other userland serializers, which don't come for free.  As davem 
said, you'll have to present a coherent namespace, that's just one of the 
annoying details.  So far you haven't said much about how such things are 
going to be handled.

--
Daniel
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