[duped]

I once improved a parser's performance a huge amount (iirc, something like 500x) when parsing large (>1GB) text files by mmap'ing the files instead of reading them into a byte array. It's not a magic bullet but it was alright for that application.

Another technique that can only be done with mmap is to map two contiguous regions of virtual memory to the same underlying buffer. This allows you to use a ring buffer but only read from/write to what looks like a contiguous region of memory.