Except for running out of VM space, all the other issues are still there. And even if you have (for the time being) practically unlimited VM space, you may still not want to mmap a file of unbounded size, since setting up all those mappings takes quite a lot of time if you're using the default 4 kB page size. So you probably want to do some kind of windowing anyway. But then if the access pattern is random and the file is large, you have to continually shift the window (munmap + mmap) and performance goes down the drain. So I don't think going to 64-bit systems tilts the balance in favor of mmap.