Mapping to host

[vinser52]

Rationale

Today, the MPI library for Level Zero and CUDA can map the device memory to the host. It is done for performance reasons: In case of short messages mapping to host and calling host memcpy works faster than copying via L0 APIs.

Description

TBD

API Changes

Need to decided on the right API

Implementation details

In case of Level Zero the Level Zero IPC API can be used. Today MPI extracts file descriptor from the IPC handle and use mmap function to map memory to the host.
In case of CUDA the gdrcopy library is used.

Meta

[bratpiorka]

@vinser52 is this needed for 0.11? if so please set the right milestone :)