[$] Unaddressable device memory

In a morning plenary session on the first day of the 2017 Linux Storage,Filesystem, and Memory-Management Summit, Ji(C)rime Glisse led a discussion onmemory that cannot be addressed by the CPU because it lives in devices likeGPUs or FPGAs. There is often a substantial pile of memory on thesedevices and it can be accessed much more quickly by the devices than thesystem RAM can be. Making it easier for user-space programmers to use thatmemory transparently is the goal of the heterogeneous memory management (HMM) patchesthat Glisse has been working on.