Using MMAP to optimize I/O access

[hariharan-devarajan]

Here are some places where we could optimize data access using MMap.

1. Producer writes
2. Broker read_all
3. consumer reading.

Additionally, we can switch the consumer file to a dyad-specific cache file on SSD so that external apps do not access it by mistake. This is because the consistency of that cache file is only known by DYAD.

[ilumsden]

Now that we are using UCX buffers, we need to make sure of the following:

• UCX-allocated buffers are page aligned
• UCX-allocated buffers comply with requirements for POSIX mmap
• UCX supports transferring data to/from specialized memory allocators (e.g., hipMalloc on El Cap)