[magicalhippo]

If your memory is paged out and you then access it, using your definition, it would block.

So, in the context of async code, there's no difference from the application perspective between reading mmap'ed data and reading "regular" data (ie memory from the regular paged pool), as both could incur blocking IO.

If you're lucky and the mmap'ed data is in the system cache, then reading that data will not block and is fast. If you're unlucky and your process has been swapped out, then doing a regular memory read will block and is slow.