Dave Hansen announced a new kernel tree focused on the development of support for hot-pluggable memory in the Linux kernel. The latest patchset is 2.6.9-rc1-mm1-mhp1, about which Dave explains:

"The main aim of this patch set (other than having the longest possible version name) is to give the memory hotplug developers a common base to work from. It is hopefully split up in such a way that it is easy to replace an implementation in the middle of the stack without disturbing too much other stuff."

Future discussion of and this tree will be found on the lhms-devel mailing list, part of the lhms project. The latest patches are against Andrew Morton [interview]'s -mm tree [story].