[$] NUMA nodes for persistent-memory management

While persistent memory is normally valued for its persistence, there is
also a subcurrent of interest in using it in settings where persistence is
not important. In particular, the fact that this memory is relatively
inexpensive makes it appealing to use instead of ordinary RAM in
budget-conscious settings. At the 2019 Linux Storage, Filesystem, and
Memory-Management Summit, two sessions in the memory-management track
looked at how the kernel's NUMA mechanism could be pressed into service to
manage non-persistent uses of persistent memory.