How much paging space is needed?

You can use these commands to determine how much paging space is being used on your system:

lsps
Gives a snapshot of the system at the time the command is issued.
topas
Shows how page space changes over the life of a process while a program is running. This command has a column marked PAGING SPACE.
svmon
Shows memory and paging space in use when you specify -G interval. The values are given in page frames. Each page frame is 4096 bytes. You can enter the svmon command once or with a time interval to monitor how paging and memory are changing.
Note: While the vmstat comand shows paging activity, it does not show clearly how much paging space is being used.

To determine how much paging space is needed, it is recommended that the paging space should be double the amount of physical memory. So if a system has 1 gigabyte of memory, the total paging space should be 2 gigabytes (although the 2 gigabytegs can be separated onto more than one disk).

On AIX you should consider the following recommendations when configuring your paging space:

  • Use the disk or disks that are least utilized.
  • Do not allocate more than one paging page logical volume for each physical disk.
  • Avoid sharing the same disk with logical volumes.
  • Make all paging spaces the same size if possible.

To make paging space available to your system, you must add and activate the paging space. The total amount of paging space is often determined by trial and error. One commonly used guideline is to double the RAM size and use that figure as a paging space target. To use the Web-based System Manager wizard, click the Volumes container, then click the Paging Space container. From the Selected menu, select Increase Page Space→Wizard.

If you prefer to use SMIT, type one of these paths on the command line:

  • To list your current paging space, type: smit lsps
  • To add paging space, type: smit mkps
  • To activate paging space, type smit swapon

When is a system thrashing? When page space becomes depleted, the operating system attempts to release resources by first warning processes to release paging space and then by killing the processes. Use the vmtune command to set the thresholds at which this activity occurs. vmtune is part of the bos.adt.smples fileset set, and it can be found in the /usr/samples/kernel directory.

For information and recommendations for changing values for your configuration, see:

  • Optimizing AIX 7.1 Peformance Tuning, which is available at http://www.ibm.com/redbooks.
  • IBM eServer pSeries Information Center, which is available at http://publib.boulder.ibm.com/infocenter/pseries/.