Re: [PATCH 1/4] x86_64: Switch to SPARSE_VIRTUAL

[Martin Bligh]

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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