linux-kernel - Re: [RFC] [PATCH] more support for memory-less-node.

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Date:	Tue, 13 Feb 2007 10:16:07 -0800
From:	"Martin J. Bligh" <mbligh@...igh.org>
To:	Christoph Lameter <clameter@....com>
Cc:	Andi Kleen <ak@...e.de>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...l.org>, bob.picco@...com
Subject: Re: [RFC] [PATCH] more support for memory-less-node.

Christoph Lameter wrote:
> On Tue, 13 Feb 2007, Andi Kleen wrote:
> 
>> Adding NULL tests all over mm for this would seem like a clear case
>> of this to me.
> 
> Maybe there is an alternative. We are free to number the nodes right? 
> How about requiring the low node number to have memory and the high ones 
> do not?
> 
> F.e. have a boundary like
> 
> nr_mem_nodes ?
> 
> Everything above nr_mem_nodes has no memory and cannot be specified in a 
> nodemask. Those nodes would not be visible to user space via memory 
> policies and page migration. So the core mempolicy logic could be left 
> untouched.
> 
> The nodes above nr_mem_nodes would exist purely within the kernel. They 
> would have proximity information (which can be used to determine 
> neighboring memory. More flexible then the current attachment 
> to one fixed memory node) but those node numbers could not be specified as 
> node masks in any memory operations. This would then allow memory less nodes 
> with I/O or cpus. The user would not be aware of these.

What's wrong with just setting the existing counters like
node_spanned_pages / node_present_pages to zero?

M.
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