pmem device dax mode; cuda pin with pmem

CONFIGURING PERSISTENT MEMORY FOR USE IN DEVICE DAX MODE

device-dax for 5.1: PMEM as RAM

"Device DAX" for persistent memory

https://pmem.io/glossary/#device-dax

https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/drivers/dax/device.c?h=v5.13.10

https://gist.github.com/edawson/a75b7e49e05ce8412f0d7fe7cb828e9c

https://docs.nvidia.com/cuda/cuda-runtime-api/group__CUDART__MEMORY.html#group__CUDART__MEMORY_1ge8d5c17670f16ac4fc8fcb4181cb490c

https://developer.nvidia.com/blog/how-optimize-data-transfers-cuda-cc/

https://www.cnblogs.com/xuyaowen/p/pinning-the-pages.html

https://sc18.supercomputing.org/proceedings/tech_paper/tech_paper_files/pap194s5.pdf (对比试验部分)

Tips: 

1. pmem+device-dax+mmap(MAP_LOCKED)+cudaHostRegister

2. pmem+fsdax+mmap(MAP_LOCKED)+cudaHostRegister