Re: memory management weirdness

[Andi Kleen]

Martin MOKREJ© <mmokrejs@xxxxxxxxxxxxxxxxxxxxxx> writes:

> Hi,
>   I have received no answer to my former question
> (see http://marc.theaimsgroup.com/?l=linux-kernel&m=110827143716215&w=2).

That's because it's a BIOS problem.

There are limits on how much Linux can work around BIOS breakage.


>   Although I've not re-tested this today again, it used to help a bit to specify
> mem=3548M to decrease memory used by linux (tested with AGP card plugged in, when
> bios reported 3556MB RAM only).
>
>   I found that removing the AGP based videoc card and using an old PCI based
> video card results in bios detecting 4072MB of RAM. But still, the machine was
> slow. I've tried to "cat >| /proc/mtrr" to alter the memory settings, but the
> result was only a partial speedup.
>
>   I'm not sure how to convince linux kernel to run fast again.

It's most likely a MTRR problem. Play more with them.


>   Finally, I put back two 512MB memory modules to have only 3GB RAM physically,
> and the result is at http://www.natur.cuni.cz/~mmokrejs/tmp/128MB/only_phys_3GB/.


The cheaper Intel chipsets don't support >4GB at all, and you always
need some space below 4GB for PCI memory mappings/AGP aperture etc.


>   About a week ago I tried to contact ASUS, but no answer so far from their
> techinical support through some web robot.
> http://vip.asus.com/eservice/techmailstatus.aspx?ID=WTM200502111723398547
> I do not recommend their "greatest" and real "flag-ship" P4C800-E-Deluxe
> motherboard for use with memory sizes above 3GB (although they claim 4GB
> is possible). BIOS is the latest release 1.19, although 1.20.001 was tested
> as well.

In general non server boards tend to be not very well or not at all
tested with a lot of memory ("a lot" is defined as >2GB for higher end
desktop boards, or >1GB on very cheap desktop boards). That is a
common problem on other motherboards too; Asus is not alone with this.

-Andi
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