linux-kernel - Re: [PATCH 1/4] x86_64: Switch to SPARSE

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Date:	Mon, 02 Apr 2007 15:41:43 -0700
From:	Martin Bligh <mbligh@...gle.com>
To:	Christoph Lameter <clameter@....com>
CC:	Andi Kleen <ak@...e.de>, Dave Hansen <hansendc@...ibm.com>,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	linux-mm@...ck.org,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [PATCH 1/4] x86_64: Switch to SPARSE_VIRTUAL

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.
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