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

Andrew Morton
2007-02-08T19:26:38Z

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