vps_ceiling.5 (2010 09)

vps_ceiling(5) vps_ceiling(5)

(Tunable Kernel Parameters)

Therefore, it is best to only raise this tunable if you know precisely the memory usage of the system. In

general, increasing the variable page size on a per application basis for known applications, such as,

databases which scan large amounts of data with only one page fault, is a much better practice.

Modern architectures support very large pages (up to 4 GB for Itanium and up to 1 GB for PA-RISC).

Setting

vps_ceiling to very large sizes (greater than 64 KB) should be done with extreme caution

since it can cause excessive memory consumption and quickly deplete the amount of free memory avail-

able on the machine.

When Should the Value of This Tunable Be Lowered?

The tunable should be lowered if physical memory fragmentation is preventing small memory processes

from running due to waiting on contiguous chunks of memory, or if the overall system usage of memory

displays poor spatial locality (virtual accesses are not close to each other) producing wasted physical

frames.

What Are the Side Effects of Lowering the Value?

Applications such as databases will suffer more page faults to get their working set into memory, but this

can be handled by using

chatr with the appropriate application.

What Other Tunables Should Be Changed at the Same Time?

vps_pagesize should be considered, being the minimum bound on the kernel heuristic range.

WARNINGS

All HP-UX kernel tunable parameters are release speciﬁc. This parameter may be removed or have its

meaning changed in future releases of HP-UX.

Installation of optional kernel software, from HP or other vendors, may cause changes to tunable parame-

ter values. After installation, some tunable parameters may no longer be at the default or recommended

values. For information about the effects of installation on tunable values, consult the documentation for

the kernel software being installed. For information about optional kernel software that was factory

installed on your system, see HP-UX Release Notes at http://www.hp.com/go/hpux-core-docs

AUTHOR

vps_ceiling was developed by HP.