AIX Tip of the Week: Improving AIX Memory Utilization on Large Systems

Audience: AIX Systems Administrators, Data Base Administrators

Date: January 1999

The default AIX memory configuration may not be optimum for systems with large memories. AIX divides memory into "file" and "working" pages. "File" pages are reserved for executables, while "working" pages are reserved for data, such as databases. The default AIX setting is appropriate for systems with smaller memories. However, in systems with larger memories, AIX can be overgenerous with memory allocated to "file" pages.

AIX can be customized to improve memory utilization. The AIX memory tuning parameter is maxperm. If the system is paging, then start looking at this setting. The following algorithm was presented in a AIX performance tuning class.

• Calculate initial setting for maxperm: (100% Memory) - %Cache - 5%
  • Assume: Real Memory = 4GB (100%)
  • Assume: Desired Cache Size = 1GB (25%)
  • maxperm= 100% - 25% -5%=70%
• Set maxperm: /usr/samples/kernel/vmtune - P70

This setting is effective until the next boot. It can be set at boot time by placing the command in /etc/rc.local.