Comment by tialaramex

I actually don't think I agree about mmap. Reading around it seems as though Mitchell had clever ideas for abusing mmap and those didn't work out. Now he's got mmap for the pages and it works so why replace it, but that does not mean you need mmap to deliver this performance and in fact I'd be extremely surprised if that were true as somebody who spent about a decade of his life mostly writing close-to-metal database code in C using mmap...

If you want a whole lot of bytes and you ask your allocator, do you know what almost any popular general purpose allocator will do on a vaguely decent modern Unix? Call mmap to get them for you. So at most you're cutting out a few CPU instructions worth of middle man.