[Gllug] 4G Memory Restriction

[Steve Nelson]

On 4/10/06, Daniel P. Berrange <dan at berrange.com> wrote:
> ... go with the HugeMem one. Ordinarily Hugemem
> would be a significant performance hit, but the AMD-64 CPUs have some
> magic which means they can avoid (all) of the performance hit associated
> with the page table split required by the 4g/4g split. So you maximise
> your 32-bit address space, giving both kernel & userspace a full 4 GB to
> play with.

Very useful.  Yes, I would like to stay on 32 bit in this instance. 
>From what's been said today, then, it seems that in my example case,
because have a 32 bit system on a 64 bit machine, the PAE and bus
width discussions are moot, as the limiting step is that the system
can only address the memory in 32 bit words.

This being the case, we want to make use of a kernel which can
maximise that addressable space.  The best way to achieve this is with
the hugemem kernels, using a  4g/4g split, which fortunately doesn't
have a performance hit on 64 bit AMD procesors.

Decent summary?

S.
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