[ggreer]

In my benchmarking, mmap() was about 20% faster than read() on OS X, but the same speed on Ubuntu. Pretty much everything else in the list (pthreads, JIT regex compiler, Boyer-Moore-Horspool strstr(), etc) improves performance more than mmap().

Also, mmap() has the disadvantage that it can segfault your process if something else makes the underlying file smaller. In fact, there have been kernel bugs related to separate processes mmapping and truncating the same file.[1] I mostly use mmap() because my primary computer is a mac.

A side note: Parts of OS X's kernel seem... not very optimized to say the least. See the bar graph at http://geoff.greer.fm/2012/09/07/the-silver-searcher-adding-... for an example.

1. http://lwn.net/Articles/357767/