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Date: Mon, 02 Apr 2007 15:41:43 -0700
From: Martin Bligh <mbligh@google.com>
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To: Christoph Lameter <clameter@sgi.com>
CC: Andi Kleen <ak@suse.de>, Dave Hansen <hansendc@us.ibm.com>,
       linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org,
       linux-mm@kvack.org, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Subject: Re: [PATCH 1/4] x86_64: Switch to SPARSE_VIRTUAL
References: <20070401071024.23757.4113.sendpatchset@schroedinger.engr.sgi.com> <Pine.LNX.4.64.0704021422040.2272@schroedinger.engr.sgi.com> <1175550968.22373.122.camel@localhost.localdomain> <200704030031.24898.ak@suse.de> <Pine.LNX.4.64.0704021534100.25602@schroedinger.engr.sgi.com>
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Christoph Lameter wrote:
> On Tue, 3 Apr 2007, Andi Kleen wrote:
> 
>> If it works I would be inclined to replaced old sparsemem with Christoph's
>> new one on x86-64. Perhaps that could cut down the bewildering sparsemem
>> ifdef jungle that is there currently.
>>
>> But I presume it won't work on 32bit because of the limited address space?
> 
> Not in general but it will work in non PAE mode. 4GB need 2^(32-21+4) = 
> 16MB pages. This would require the mapping on 4 4MB pages.

IIRC NUMA isn't supported (or useful anyway) without PAE.

> For 64GB you'd need 256M which would be a quarter of low mem. Probably 
> takes up too much of low mem.

Yup.


M.