HP-UX 11i v3 Installation and Update Guide, September 2007 (Update 1 Release)

Conclusion
VxFS uses in-memory caches for objects that result in improved file system performance.
The cache sizes are controlled by tunables that are auto-tuned at boot time by the driver.
For situations where the auto-tuned values are not optimal, you can set these tunables.
134 Controlling Memory Utilization of VxFS 4.1