It sounds as though you do indeed have a memory leak somewhere rather than just a misunderstanding of the memory statistic numbers. However, I'm quite certain that the problem has nothing to do with the kernel, but rather a leak in one of the apps you are running. If you say that even after shutting down all the apps you are still thrashing, then I would suspect the problem is probably with KDE or one of the libraries it uses or something with X. Also, occassionally when closing an app that has a problem, even though the window disappears, sometimes the program continues running and using your memory. Use top to check this. Rebooting should not be necessary. See if restarting X solves the memory problem.
Gerry > In theory, this is fine. But on my system (512 MB RAM) it's not always like > that. After a few hours of work with a lot of opening apps and documents and > images, it dips into swap, and it does that even when I close most apps. So > before I can continue working I have to reboot. This shouldn't be necessary. > Is it because I have a 'pre' kernel? I wondered why they made the 2.2.18pre21 > the default kernel for potato when they otherwise put software in it that are > sometimes not usable because they're so ancient.