HP Process Resource Manager User's Guide

Understanding how PRM manages resources
How PRM manages real memory resources
Chapter 2 53
from when needed. So, in this example, the prmavail command would
show 850 Mbytes of available memory before PRM is configured, and 756
Mbytes of available memory after PRM is configured.
How PRM controls memory usage
PRM memory management allows you to prioritize how available
memory is allocated to user and application processes. This control
enables you to ensure that critical users and applications have enough
real memory to make full use of their CPU time.
When PRM first starts and is configuring memory management, the
PRM_SYS group (PRMID 0) is in control of all usable memory on the
system. The memory not needed by processes in PRM_SYS, known as
available memory, is the memory reported by prmavail. This remaining
memory is allocated to the other PRM groups, according to their
entitlements. The amount of available memory may fluctuate up or down
based on the needs of the kernel, buffer cache, daemons, and other
processes in PRM_SYS.
PRM’s memory management is controlled by the daemon prm2d. This
daemon uses an in-kernel memory feature to partition memory (when a
configuration is loaded), with each PRM group getting a partition. Each
partition includes x Mbytes of memory, where x Mbytes is equivalent to
the group’s entitled percent of the available memory or the requested,
fixed-size shared memory allocation. Each partition pages separately.
When system memory use is not at 100%, a PRM group that does not
have its memory use capped or isolated can freely borrow excess memory
pages from other PRM groups. If a process requires memory and its
memory use is capped, processes in the same PRM group as the original
process are forced to page to free up memory.
Table 2-6 Example of available memory on a 1024-Mbyte system
Mbyte Memory type
1024 Physical memory available on the system
912 Memory available for all processes
850 Memory available for user processes
756 Memory available after PRM is configured