Comment by zozbot234

> If the file is mmap'd, and the string view points into that, presumably decent performance depends on the page cache having those strings in RAM.

Not so much, because you only need some fraction of that memory when the program is actually running; the OS is free to evict it as soon as it needs the RAM for something else. Non-file-backed memory can only be evicted by swapping it out and that's way more expensive,