“With mmap, you just point to the data you want. If it’s bigger than memory …. so what?”
And if it’s bigger than your address space…? (“My solution scales so much better than your solution, right up to the point where it catastrophically stops scaling.”) I feel the rant tag is appropriate here, if only for comparing best case apples to worst case oranges.
I’d worry about the data being distributed even more than swamping a 64-bit address space.
Although, IIRC, the APL-family of languages have more to offer than just mmap — I wouldn’t adopt or abandon the languages on such a trivial analysis.