A patch for 2.0.21/22 exists in the contrib section of etherboot-3.0b2
(found on sunsite). I have it running on 4 diskless machines (2 are PPP
servers, 1 is just a web browser, and the fourth is an XDM terminal) with
no problem whatsoever.
If memory serves, it applies cleanly through 2.0.26/27, then you have to
do a little bit of cleanup work. I currently am running with 2.0.28 on
those machines, and don't have any plans to upgrade them until swapping is
in the kernel tree for good.
For conveinance, I've placed the patch & such at:
http://www.vu.union.edu/~hagopiar/linuxnfsswap/
and
ftp://ftp.vu.union.edu/pub/users/hagopiar/linuxnfsswap
-Rob H.