fc1_x86_64 preview on tyan thunder k8w (S2885ANRF REV .03)

[Alan Cox]

On Thu, Dec 11, 2003 at 04:11:26PM -0600, Thomas Dodd wrote:
> It was sort of explained before by Mark. What was ment is you _cannot_ 
> use the last .5G because it's mapped to PCI.

Thats the physical memory map. Because PCI is 32bit for some cards you 
end up with a PCI hole (remember the ISA hole.. now we have two 8))

So its

  0-639K		RAM
  640K-1Mb		ISA + ROM window
  1Mb-3.5Gb		RAM
  3.5Gb-4Gb		PCI plus ROM plus APIC etc
  4Gb->...		RAM
  

> There may be some trick to move that though. I remember this was a 
> problem for 32bit too. PCI+kernel took the last 1GB on a 4GB box, so 
> processes only got 3GB. There were sopme hack to get 3.5GB on those, so 
> it might be posible to get more on 64bit systems. Maybe only loose 0.25GB?

Thats different. You end up needing some mappings for kernel and user
space to be efficient when dealing with user mappings. Whether you can
get your .5Gb back depends if the chipset can remap it higher up in memory
so that the 3.5-4Gb RAM masked by PCI is remapped at the top of memory.

Alan