Note to the puzzled: skip down to "TTY-based group scheduling" - this explains what the {200|4} line patches are doing.
Thanks, I understand somewhat after i read this.
because a 200 line kernel change is not the same as 4 line shell-script change. fwiw, i had posted that many a moons ago here : http://lwn.net/Articles/414817/.
The linked LWN article does indeed discuss the 4 line shell-script.