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SubjectRe: Opteron box and 4Gb memory
J.A. Magallon wrote:
> Hi...
>
> I have some Quad-Opteron boxes with 4Gb memory and two of them are
> running two different Linux distros.
>
> Box one sees 4Gb of memory, but box two just sees 3.
> Their mtrr setups are different:
>
> Why ? Is it a bios setup problem ? A kernel problem ?
> grep HIGHMEN in configs for both kernels does not give anything, so
> I still understand less this thing...
>

It would depend on how the BIOS programmed the memory controllers. For
32-bit (and lots of device) compatibility, a memory hole is required
below 4 GB. Not all memory controllers can remap memory in the 3-4 GB
range above the 4 GB memory; I'm not sure if that varies with the
different Opteron processors.
Also, if you run a 32-bit distribution, you need to have HIGHMEM_64G
enabled in the kernel.

-hpa
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