We have a Linux server for which Cacti's memory usage graph reports decreasing cache size until the server eventually runs out of memory. Free memory remains low throughout, which is normal for Linux. I would expect cache size to remain roughly constant over time, and I'm trying to think of what might possibly be going on with this.
I assume that a kernel memory leak is not a likely issue.
I also saw this, which says that saving to a tmpfs filesystem is a possibility:
Any others I should be looking at?