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SubjectRe: x86 patches was Re: -mm merge plans for 2.6.24
> On Tue, 2 Oct 2007 00:43:24 -0700
> Andrew Morton <akpm@linux-foundation.org> wrote:
>
> > On Tue, 2 Oct 2007 16:36:24 +0900 KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.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.

From memory-hotplug view, memory-less node is very helpful.
It can define and arrange some "halfway conditions" of node hot-plug.
I guess that node unpluging code will be simpler by it.


Bye.

--
Yasunori Goto


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