linux-kernel - Re: x86 patches was Re: -mm merge plans for 2.6.24

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Message-Id: <20071002171631.46888326.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Tue, 2 Oct 2007 17:16:31 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org,
	mpm@...enic.com, "Huang, Ying" <ying.huang@...el.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Christoph Lameter <clameter@....com>, apw@...dowen.org,
	"Lee.Schermerhorn@...com" <Lee.Schermerhorn@...com>
Subject: Re: x86 patches was Re: -mm merge plans for 2.6.24

On Tue, 2 Oct 2007 00:43:24 -0700
Andrew Morton <akpm@...ux-foundation.org> wrote:

> On Tue, 2 Oct 2007 16:36:24 +0900 KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> 
> > > Don't think so.  A node is a lump of circuitry which can have zero or more
> > > CPUs, IO and memory.
> > > 
> > > It may initially have been conceived as a memory-only concept in the Linux
> > > kernel, but that doesn't fully map onto reality (does it?)
> > > 
> > > There was a real-world need for this, I think from the Fujitsu guys.  That
> > > should be spelled out in the changelog but isn't.
> > 
> > Yes, Fujitsu and HP guys really need this memory-less-node support. 
> > 
> 
> For what reason, please?
> 

For fujitsu, problem is called "empty" node.

When ACPI's SRAT table includes "possible nodes", ia64 bootstrap(acpi_numa_init)
creates nodes, which includes no memory, no cpu.

I tried to remove empty-node in past, but that was denied.
It was because we can hot-add cpu to the empty node.
(node-hotplug triggered by cpu is not implemented now. and it will be ugly.)


For HP, (Lee can comment on this later), they have memory-less-node.
As far as I hear, HP's machine can have following configration.

(example)
Node0: CPU0   memory AAA MB
Node1: CPU1   memory AAA MB
Node2: CPU2   memory AAA MB
Node3: CPU3   memory AAA MB
Node4: Memory XXX GB

AAA is very small value (below 16MB)  and will be omitted by ia64 bootstrap.
After boot, only Node 4 has valid memory (but have no cpu.)

Maybe this is memory-interleave by firmware config.

Thanks,
-Kame

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