"high memory" issue

[Karl Hegbloom]

On Sat, 2006-03-18 at 13:12 +0100, Colin Brace wrote:
> I added a second 521 MB SIMM to my Pentium M laptop, but it adversely
> affected peformance; it slowed the system way down. Vendor says it has
> something to do with "a high memory conflict", and he advised adding
> 'mem=512' to the grub kernel parameters as a temporary measure while
> he investigates further. After doing so, system runs normally again
> but of course only sees 512MB. A Google search returns some hits but
> mostly from three or four years ago with older kernels, ie, 2.4 and
> earlier. Anyone have any ideas on how to solve this? I am running
> Breezy with the 2.6.12-10 kernel

You don't need mem=512M, but rather mem=1008M, if you've 1024M of RAM
installed.  My laptop has the same problem.  You can press ESC when the
grub message is printed, to get a menu.  There, press 'e' over the entry
you want to boot, and then arrow down to the 'kernel' line, and press
'e' again.  At the end of the command line, type a space, and then the
mem=1008M, and press Enter.  'b' will boot the computer.

After it's booted, edit /boot/grub/menu.lst to add that to the command
line, OR, if you want to get the use of that last few megabytes of RAM,
you can drop the attached script into /etc/mkinitramfs/scripts/init-top,
and then rebuild the initramfs image with:

 sudo mkinitramfs -o /boot/initrd.img-$(uname -r) $(uname -r)

Reboot _without_ the mem= option, and you should have full-speed and all
of the available RAM (minus the amount used for the kernel itself).

I wish that somebody who can understand the MTRR code in the Linux
kernel would fix it for us... but for now, that script makes it work.
What it does is tell the system to cache all of the RAM.  Without it, it
was not using the cache for some of it, slowing the machine to a crawl.

Another option is to patch the linux-source with the "1g_lowmem.patch":

 http://kerneltrap.org/node/6067

... then run 'make menuconfig', set it to use 1G Lowmem, and rebuild,
then reinstall.  There are probably instructions on the Ubuntu Wiki.

Please forward this to your vendor.

-- 
Karl Hegbloom <hegbloom at pdx.edu>
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