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

From: Jack Steiner <>
Date: 2005-11-10 13:54:21
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=16384
> >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 

> 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


Jack Steiner (          651-683-5302
Principal Engineer                      SGI - Silicon Graphics, Inc.

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Received on Thu Nov 10 13:55:06 2005

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