How do you limit the pagecache size in opensuse 11.4

How do you put a limit in place for file caching in Suse 11.4?

My pc becomes usable on a regular basis with minimum cpu usage because I can’t open new applications
There are no error messages etc, the new apps just don’t open.

free -m shows the vast majority of my memory is used by cache
free -m
total used free shared buffers cached
Mem: 3185 1048 2137 0 38 503 (this becomes max)
-/+ buffers/cache: 506 2679
Swap: 2055 0 2055

I’ve done …
echo 3 > /proc/sys/vm/drop_caches

Sometimes an app will open after this but the system becomes unstable, locking up regularly.

I not sure why the default max is 100% file cache but I’d to put a sane file cache limit in place, like 40% or something.
I’ve put limits in place in the past using a percentage and I’ve poked arround but i don’t see the setting.

Thanks