Why this paper
pSeries® nodes with large memories are often used for applications that expect
to use all the available real memory, either for one serial application or in
aggregate for the tasks of a parallel MPI job running on the node.
If an application accesses real memory beyond the amount available, AIX® 5L™
provides support for paging out less frequently used pages. However, paging is
relatively slow compared to central processing unit (CPU) speeds, and adversely
affects the critical performance requirement of these applications. Excessive
paging can disrupt efficient application execution.
This paper describes mechanisms to help applications use maximum available
real memory while protecting the integrity of the node. We achieve this by
reducing the risk of paging by applications that demand more real memory than
© Copyright IBM Corp. 2006. All rights reserved.
In this Redpaper we address the following items:
We describe how to determine the base amount of real memory available on
a node that is operational with all required system daemons and devices
initialized, but no application work running. There are some differences
between the procedure for AIX 5L Version 5.2 and AIX 5L Version 5.3.
We describe the characteristics of the Workload Manager (WLM) component
in AIX 5L that relate to real memory control.
We discuss the control of parallel MPI jobs using the Parallel Environment for
AIX 5L and LoadLeveler® products. There is a subsection on configuring
LoadLeveler to use the WLM absolute real memory limit to control memory
used by LoadLeveler jobs. There is also a subsection on how to specify
memory requirements for LoadLeveler jobs.
We discuss related topics and suggestions for future investigations.
Determining available real memory
This section describes the process for determining th