The attached patch is a prototype implementation of memory hot-add.  It
allows you to boot your system, and add memory to it later.  Why would
you want to do this?  Well, it's a step before memory removal which can
help cope with things like bad RAM.  This is primarily useful for a
machine that you don't want to reboot during an upgrade.

For instance, on my 1GB laptop, I booted with mem=512M on the kernel
command-line.  Once I had booted, I did the following:

cd /sys/devices/system/memory
echo 0x20000000 > probe
echo 0x30000000 > probe
echo online > memory2/state
echo online > memory3/state

and the last 512MB of my laptop's memory was onlined.  The onlining
operations can occur from an /etc/hotplug script if desired.

Here's the config file that I used:
http://www.sr71.net/patches/2.6.11/2.6.11-rc3-mhp1/configs/config-i386-T41-laptop

The important config options are:
CONFIG_MEMORY_HOTPLUG=y 
CONFIG_SPARSEMEM=y
CONFIG_SIMULATED_MEM_HOTPLUG=y

This patch depends on the previously posed "Sparse Memory Handling
(hot-add foundation)" patch.

There are a number of individual patches (with descriptions) which are
rolled up in the attached patch: all of the files listed after
"G2-no-memory-at-high_memory-ppc64.patch" from this directory:
http://www.sr71.net/patches/2.6.11/2.6.11-rc3-mhp1/broken-out/

I can post individual patches if anyone would like to comment on them.

-- Dave