Re: [RFC] 4-level page table directories.

Jack Steiner
2005-11-10T02:54:21Z

On Wed, Nov 09, 2005 at 04:27:48PM -0800, Luck, Tony wrote:
> >Is it possible you are mixing up MAX_NUMALINK_NODES (the maximum
> >system size, i.e., the maximum number of nodes in a numalink domain)
> >with CONFIG_NR_CPUS (the maximum SSI size)?
> >
> >I'm pretty confident SGI has not proposed setting CONFIG_NR_CPUS\x16384
> >to any OSV. ;-)
>
> It's always possible that I'm confused. Here's the message where
> Robin introduced the rationale for 4-level page tables:

You are not confused, but this is a confusing area. A lot of
the terminology that we use to describe these configurations has
been misused or poorly defined.

Altix currently supports a max SSI of 256 nodes (1024p). However, multiple
SSIs can be interconnected via NUMALINK.

XPMEM provides the ability for a single task running within an SSI
to access ALL the memory thruout the NUMALINK fabric, ie. memory
can be exported from a task running within one SSI to a task
running in another SSI.

For example, if you have:

128 GB per SSI
16 SSIs connected via NUMALINK

a task running within an SSI can access all 2TB of memory (excluding memory
used by the kernel)

Note: SSI = fat node = cluster

>
> http://tinyurl.com/bewsk
>
> In that he says "current = 2048" ... which I think is how many
> cpus can be in the whole box ... 512 is the current max cpus in
> a coherence domain (and thus the max that a single instance of
> Linux will see today).
>
> With Montecito (dual core, two threads in each core) the number
> of cpus Linux sees will be quadrupled in a system with the same
> number of sockets. Add more sockets, and the 16384 number may
> not be impossible.
>
> -Tony

--
Thanks

Jack Steiner (steiner@sgi.com) 651-683-5302
Principal Engineer SGI - Silicon Graphics, Inc.