vps_pagesize.5 (2010 09)

vps_pagesize(5) vps_pagesize(5)

(Tunable Kernel Parameters)

Modern architectures support very large page sizes (up to 4 GB for Itanium and up to 1 GB for PA-

RISC). Setting the value very high (greater than 64 KB) can cause excessive memory consumption and

quickly deplete the free memory on the system.

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?

vps_ceiling is lowered as well, applications with large data sets (such as databases) may suffer a

performance degradation due to increased page faults. This can be corrected with a

chatr of the

appropriate application. If

vps_ceiling is not modiﬁed, the side effects should be minimal as the ker-

nel will now have a larger range to choose an appropriate page size for each application not changed with

the chatr command.

What Other Tunables Should Be Changed at the Same Time?

vsp_ceiling 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_pagesize was developed by HP.