Active Memory Expansion (AME)

To enable AME, you first need to verify if the managed system supports Active Memory Expansion.

1. From the Hardware Management Console, select the managed system you want to check.
2. Open the 'Properties' for the selected system.
3. Go to the 'Capabilities' tab.
4. Look for the entry "Active Memory Expansion Capable."
5. If it shows "True", the system supports Active Memory Expansion.

There are no limits on the number of logical partitions that can use AME within a system. You can enable AME for a specific partition while leaving others disabled.

Active Memory Expansion requires a charge for permanent enablement per managed system, or you can opt for a 60-day trial via Capacity on Demand to test in your environment.

The screenshot above shows a system that is not capable of supporting Active Memory Expansion.

Active Memory Expansion (AME) should be activated through the Hardware Management Console.

1. To enable AME for an LPAR, edit the partition's profile.
2. Navigate to the Memory tab.
3. Look for the "Activate Memory Expansion" option.
4. Check the box to enable AME.
5. You can also specify the active memory expansion factor in the provided text box.

A hard reboot is required to complete the activation of AME. This involves shutting down the LPAR and then restarting it through the Hardware Management Console to apply the changes made to the LPAR's profile.

Once the logical partition is back up, AME will become enabled. To confirm, use the command lparstat -i, which will display "Memory Mode: Dedicated-Expanded."

The expansion factor can range from 1.00 to 10.00. 

Setting the expansion factor to 1.00 is not recommended, as it will not result in any memory expansion. Additionally, a factor of 10.00 has not been commonly used.

You can adjust the expansion factor using the dynamic logical partitioning (DLPAR) feature. Through DLPAR, you can modify the expansion factor when adding or removing memory.

To dynamically adjust the Active Memory Expansion factor for a logical partition, follow these steps using the HMC:

1. In the navigation pane, go to Systems Management > Servers and select the managed system where the logical partition is located.
2. In the contents pane, choose the logical partition for which you want to change the Active Memory Expansion factor.
3. From the Tasks menu, select Dynamic Partitioning > Memory > Add or Remove. This will open the Add/Remove Memory Resources window.
4. In the Active Memory Expansion field, enter a value between 1.00 and 10.00.
5. Click OK to apply the changes.

The Active Memory Expansion Planning Tool is required to complete the configuration. This tool can also be used later to assess the performance of Active Memory Expansion. It recommends the optimal expansion factor for the partition to handle peak workload times effectively.

The Active Memory Expansion Planning Tool, known as amepat, performs several key functions:

• It scans current memory usage to determine if a workload could benefit from the AME feature.
• It provides a list of possible expansion configurations for the workload.
• It records expected CPU utilization for each expansion factor.
• It aims to maximize memory savings while minimizing additional CPU usage.
• It monitors and analyzes system configuration, workload, and performance statistics with AME.
• It logs system configurations and various performance statistics into a file.
• It generates workload utilization and planning reports.

amepat can be executed on both partitions with AME enabled or disabled. If AME is disabled, it can suggest an appropriate expansion factor.

This tool is compatible with all IBM Power Systems servers running AIX 6.1 or later.

It helps suggest the best expansion factor based on peak workload times and provides insights into the CPU cycles needed to work with AME. Additionally, it displays detailed memory information, including pinned memory, file cache, virtual memory, and true memory.

By default, ame_mpsize_support tunable is set to 0. This value enables legacy behavior in an AME environment, where only the 4 KB and 16 MB page sizes are supported. Setting the value to 1 enables all supported page sizes in an AME environment. This tunable parameter can only be modified on POWER8 or later processor-based servers, which support the 64 KB page size accelerator.

To enable 64 KB pages, you can run the following command:

# vmo -ro ame_mpsize_support=1

Note: This change requires a bosboot and a reboot.

Active Memory Expansion can compress memory pages used by applications on the system. However, it will not work for certain memory pages. Specifically, Active Memory Expansion does not compress or apply to the following memory pages:

• AIX kernel
• Filesystem cache
• Pinned memory

Use the command # vmstat -P all to check for the presence of different page sizes.

Use the amepat tool to determine the appropriate and suggested expansion factor. Run amepat for one hour to record Active Memory Expansion data into the specified recording file.

It is recommended to execute amepat during periods of high workload in your environment. Use the -R flag to record Active Memory Expansion data into the specified file. This recorded data can later be processed using the -P option.

To run amepat in the background for one hour, use the command:
# amepat -R ame.int 60

You will see the message: "Continuing Recording through background process..."

To check if the amepat process is running, use the command:
# ps -ef | grep amepat

The output will be written to the ame.int file, which can be processed later.

We recommend running multiple reports during other high-workload periods. If the workload is low, the report may suggest shrinking the memory.

Once the amepat command completes (typically after one hour or slightly longer), use the command # amepat -P ame.int to process the ame.int file and generate a report.

You can also use the -t flag to specify a target size for modeling instead of relying on the calculated one. For example, if you specify a target size of 4.00 GB in the ame.int file, the tool might recommend increasing the assigned memory to 2.50 GB with an expansion factor of 1.6, which would bring the total memory to 4.00 GB, as specified with the -t flag.

Use lparstat -c 1 to monitor CPU usage by Active Memory Expansion (AME). The following statistics are shown only when the -c flag is used:

• %xcpu: Indicates the percentage of CPU utilization dedicated to Active Memory Expansion (AME) relative to the total CPU consumption by the logical partition.
• xphysc: Displays the number of physical processors being used for the Active Memory Expansion activity.
• dxm: Shows the size of the expanded memory deficit for the LPAR, measured in MB.

Use the svmon command with the following syntax:
# svmon -G -O summary=ame -O pgsz=on

The output will display memory usage information, and if no 64K pages are present, it will indicate that.

To disable Active Memory Expansion (AME), follow these steps:

1. Edit the logical partition profile and open the Memory tab.
2. Uncheck the box next to 'Activate Memory Expansion.'
3. Shut down the logical partition.
4. Reactivate the logical partition from the HMC through its profile.
5. Confirm that AME is disabled by running the command lparstat -i; the Memory Mode will display as "Dedicated."

• AIX Performance Management article on AME, detailed insights and useful commands for monitoring AME
• AIX 7.2 AMEPAT command manual page for the Active Memory Expansion Planning Tool