The first implementation of this algorithm was actually a file system, done in assembler using 5-hole ``Baudot'' paper tape for a drum storage device attached to a 20 bit germanium transistor computer with 2000 words of memory, but that was many years ago.
Peter Wemm <peter@FreeBSD.org> came up with the idea to store the page-directory in mmap(2)'ed memory instead of in the heap. This has proven to be a good move.
Lars Fredriksen <fredriks@mcs.com> found and identified a fence-post bug in the code.