With a run-time check you don't have to sacrifice anything, the binary is still portable everywhere, but can also use MAP_TRYFIXED for better performance if it exists in the running kernel.
Except that if you build it on a machine which knows about MAP_TRYFIXED at all, the resulting binary's not likely to run on older machines...
-- Jon Bright Silicon Circus Ltd. http://www.siliconcircus.com
