linux-kernel - Re: [2.6.20][PATCH] fix mempolicy error check on a system with memory-less-node

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Message-Id: <20070208112629.3a4ce158.akpm@linux-foundation.org>
Date:	Thu, 8 Feb 2007 11:26:29 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Christoph Lameter <clameter@....com>
Cc:	Andi Kleen <ak@...e.de>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	LKML <linux-kernel@...r.kernel.org>,
	GOTO <y-goto@...fujitsu.com>,
	Christoph Lameter <clameter@...r.sgi.com>
Subject: Re: [2.6.20][PATCH] fix mempolicy error check on a system with
 memory-less-node

On Thu, 8 Feb 2007 11:09:40 -0800 (PST) Christoph Lameter <clameter@....com> wrote:

> > > > and to 
> > > > accurately present the machine's topology to the user without us having to
> > > > go adding falsehoods like this?
> > > 
> > > a node is a piece of memory. Without memory it doesn't make sense.
> > 
> > Who said?  I can pick up a piece of circuitry which has four CPUs and no
> > RAM, wave it about then stick it in a computer.  The kernel is just wrong,
> > surely?
> 
> Surely your computer has some memory so attach it to that memory (which 
> in a NUMA system would be one or the other node).

"attach it".  But it _isn't_ attached.  There is no memory on this node. 
We seem to be saying that we should misrepresent the physical topology
because the kernel doesn't handle it appropriately.

> Cpu only "nodes" would mean that all memory would be off node. Meaning 
> whatever interconnect one has would be heavily used. Operating system and 
> application performance will suffer.

>From this a logical step would be to change the kernel to refuse to bring
memoryless nodes online at all.

If that's not an approproate solution, then there must be a legtimate
reason for using memoryless nodes.  

Which is it?
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