Messages in this thread | | | Date | Thu, 25 Oct 2007 14:58:10 -0700 | From | "H. Peter Anvin" <> | Subject | Re: Opteron box and 4Gb memory |
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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.
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