Re: lost memory on a 4GB amd64

[Andi Kleen <ak@muc.de>]

[cc'ed to discuss@x86-64.org for future reference. If you find
this message in google and you have the same problem, talk
to your BIOS vendor, not to your Linux vendor]

On Sat, Oct 23, 2004 at 12:02:10PM +0200, Andreas Klein wrote:
> - Tyan S2885 pre-production model with a 1.01 pre-release bios
> 6 mb ram (4x512mb, 4x1gb)
> The machine is running SuSE Linux Enterprise Server 8 (32bit).
> We use this machine as our primary mail-server without problems for over a 
> year.
> 
> - Now we ordered 45 Tyan S2885 and 4 S2875S board.
> Both board do not run stable with more than 2GB ram usable.
> 4GB will only be recognized if the MTRR setting is set to Continuous and 
> the Adjust Memory setting is set to Auto.
> If the bios is configured this way and two 1gb ram modules are installed 
> for each CPU on the 2885, the machine will not even load and unpack a 
> SLES 9 kernel. Memtest sees 0-2GB mem usable and 4-6GB unusable (complains 
> about each memory address).
> If all four modules are installed for CPU0, then memtest seems to work 
> without problems (0-2GB, 4-6GB), but SLES9 will crash during boot-up.
> If all four modules are installed for CPU1, then memtest seems to work 
> without problems too. SLES 9 will run a few minutes before a crash.
> I will try to install SLES 8 (32bit) on the new boxes to see if it runs 
> stable. If yes, there is something broken in the 2.6 kernels for amd64, if 
> not, the pre-production bios is better that the final ones.

It all sounds very much like a BIOS problem. I doubt 2.4 will
run stable on this setup - if memtest86 doesn't like the memory, Linux 
won't like it neither. All I can recommend is to talk to Tyan or
live with the lost memory. 

-Andi