Heterogeneous Memory Management Still Being Worked On For Nouveau / Radeon / Intel
Heterogeneous Memory Management was merged in Linux 4.14 as one of the kernel pieces sought after by NVIDIA and other vendors. HMM allows a process address space to be mirrored and system memory to be transparently used by any device process.
NVIDIA has worked out the support for their proprietary driver but since its merger to mainline we haven't seen much other mainline code adapted to make use of this... But Jerome still has out-of-tree code. He had been focusing a lot on the Nouveau HMM support but now he also has working branches of the Intel and Radeon drivers supporting this functionality as well, which is important for compute/OpenCL and other purposes.
The latest code work he's prepping to HMM itself is improving the synchronization callback and various fixes. For the next kernel cycle, Linux 4.20~5.0, he is hoping to merge more prep work but is going to wait on landing the actual driver support until these patches have been merged upstream.