how to page_cache.max_percent?

hi,

the following scenario:

 * kernel 2.4.9 smp
 * machine with 6GB physical memory
 * multiple processes are relying on a 3GB large data structure
   to be in memory (speed goes down the drain, when some pages 
   are swapped out)
 * not every page in this 3GB data structure is used all the time
 * this data structure is loaded from files, so initially
   i end up having 3GB of used cache (visible in vmstat)

now i start another memory intense process and discover via vmstat
the following sensible behaviour: pagecache shrinks slowly and
memory from the 3GB structure is swapped out at a faster rate...

i don't care about the pagecache, i only care about having those
3GB in memory... 

is there a way to set a maximum size for the pagecache (afaik,
page_cache.max_percent is not used)?

or can i specify to always drain the pagecache before swapping out?

cheers,
-iowa