mtrr funnies
Roger Heflin
rogerheflin at gmail.com
Sat Oct 11 23:32:00 UTC 2008
Wolfgang S. Rupprecht wrote:
> I've got a motherboard with a fairly new chipset (Asus M3A78T
> w. AMD/ATI 790GX) and I'm seeing a funny MTRR setting. I have 8GB
> memory and am running a 64-bit kernel, but I'm only seeing ~4GB
> mentioned in the MTRR's. Is this a bug? Do I need to add the upper
> 4+GB by hand?
>
> $ cat /proc/mtrr
> reg00: base=0x00000000 ( 0MB), size=2048MB: write-back, count=1
> reg01: base=0x80000000 (2048MB), size=1024MB: write-back, count=1
> reg02: base=0xc0000000 (3072MB), size= 256MB: write-back, count=1
> reg03: base=0xd0000000 (3328MB), size= 256MB: write-combining, count=1
>
> It does seem like the kernel sees the whole memory, at least at times,
> but it isn't clear if that high memory is being cached the right way.
>
> Oct 7 10:54:30 poblano kernel: Memory: 7678940k/8650752k available (2699k kernel code, 184672k reserved, 1485k data, 980k init)
>
> -wolfgang
On the AMD's I remember one of the AMD experts mentioning that the >4GB memory
stuff is automagic so is not listed as a MTRR at all. It is just there.
Does "cat /proc/meminfo" and top both show around 8GB like expected?
Roger
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