Re: [patch 2/2] enables booting a NUMA system where some nodes have no memory

Jack Steiner
2006-11-16T01:35:51Z

On Wed, Nov 15, 2006 at 02:40:36PM -0800, Christoph Lameter wrote:
> On Wed, 15 Nov 2006, Jack Steiner wrote:
>
> > A lot of the core infrastructure is currently missing that is required
> > to describe IO nodes as regular nodes, but in principle, I don't
> > see anything wrong with nodes w/o memory.
>
> Every processor has a local node on which it runs. The kernel places
> memory used by the processor on the local node. Even if we allow
> nodes without memory: We still need to associate a "local" node to the
> processor. If that is across some NUMA interlink then it is going to be
> slower but it will work.

True.

>
> AFAIK It seems to be better to explicitly associate a memory node with a
> processor during bootup in arch code.
>
> Various kernel optimizations rely on local memory. Would we create
> a special case here of a pglist_data structure without a zones structure?
>
> It seems that the contents of pglist_data are targeted to a memory node.
> If we do not have a pglist_data structure then the node would not exist
> for the kernel.
>
> What would the benefit or difference be of having nodes without memory?

I doubt that there is a demand for systems with memoryless nodes. However, if the
DIMM(s) on a node fails, I think the system may perform better
with the cpus on the node enabled than it will if they have to be
disabled.

-- jack