HP-UX Workload Manager User's Guide

Understanding how PRM manages resources
Management of real memory
Appendix F450
Capping memory use
You can optionally specify a memory cap (upper bound) for a workload
group using the gmaxmem keyword in your WLM configuration, as
explained in “Specifying a group’s maximum memory (optional)” on
page 184. Typically, you might choose to assign a memory cap to a
workload group of relatively low priority, so that it does not place
excessive memory demands on the system.
NOTE Processes in the PRM_SYS group (ID 0) and the kernel are not subject to
memory capping.
Management of locked memory
Real memory can be locked (that is, its pages kept in memory for the
lifetime of a process) by the kernel, by the plock() system call, or by the
mlock() system call.
Locked memory cannot be paged or swapped out. Typically, locked real
memory holds frequently accessed programs or data structures, such as
critical sections of application code. Keeping them memory-resident
improves system performance. Locked memory is extensively used in
real-time environments, like hospitals, where some processes require
immediate response and must be constantly available.
With the prm2d memory manager, locked memory is distributed based on
the assigned memory allocations. For example, assume a system has 200
Mbytes of available memory, 170 Mbytes of which is lockable. Lockable
memory divided by available memory is 85%. If GroupA has a 50%
memory allocation, it gets 100 Mbytes of real memory. Of that amount,
85% (or 85 Mbytes) is lockable. Notice that 85 Mbytes/170 Mbytes is
50%, which is the group’s memory allocation. Figure F-1 illustrates this
idea.