Before AME is activated for the first time, it is advisable to first use the amepat tool (Active Memory Expansion Planning Tool) on the LPAR concerned. The tool analyzes the existing workload on a system and determines how well the data can be compressed. Based on the data collected during the run, some AME factors are listed with the estimated CPU usage and finally a recommendation for a configuration is given:

aix09 # amepat 10
 
Command Invoked                : amepat 10 
 
Date/Time of invocation        : Sun May 30 18:30:25 CEST 2021
Total Monitored time           : 28 mins 19 secs
Total Samples Collected        : 3
 
System Configuration:
---------------------
Partition Name                 : aix09
Processor Implementation Mode  : POWER8 Mode
Number Of Logical CPUs         : 32
Processor Entitled Capacity    : 0.80
Processor Max. Capacity        : 8.00
True Memory                    : 144.00 GB
SMT Threads                    : 4
Shared Processor Mode          : Enabled-Uncapped
Active Memory Sharing          : Disabled
Active Memory Expansion        : Disabled
 
System Resource Statistics:                 Average              Min               Max
---------------------------               -----------        -----------        -----------
CPU Util (Phys. Processors)               0.81 [ 10%]        0.77 [ 10%]        0.87 [ 11%]
Virtual Memory Size (MB)                 73009 [ 50%]       73001 [ 50%]       73013 [ 50%]
True Memory In-Use (MB)                 116923 [ 79%]      116913 [ 79%]      116928 [ 79%]
Pinned Memory (MB)                       16273 [ 11%]       16273 [ 11%]       16273 [ 11%]
File Cache Size (MB)                     43540 [ 30%]       43538 [ 30%]       43542 [ 30%]
Available Memory (MB)                    69757 [ 47%]       69754 [ 47%]       69765 [ 47%]
 
Active Memory Expansion Modeled Statistics:
-------------------------------------------
Modeled Expanded Memory Size   : 144.00 GB
Average Compression Ratio      :   2.78
 
Expansion    Modeled True      Modeled              CPU Usage  
Factor       Memory Size       Memory Gain          Estimate     
---------    -------------     ------------------   -----------     
     1.03        140.00 GB         4.00 GB [  3%]   0.00 [  0%]
     1.22        118.25 GB        25.75 GB [ 22%]   0.00 [  0%]
     1.41        102.25 GB        41.75 GB [ 41%]   0.00 [  0%]
     1.60         90.25 GB        53.75 GB [ 60%]   0.00 [  0%]
     1.79         80.50 GB        63.50 GB [ 79%]   0.00 [  0%]
     1.98         72.75 GB        71.25 GB [ 98%]   0.00 [  0%]
     2.17         66.50 GB        77.50 GB [117%]   0.14 [  2%]
 
Active Memory Expansion Recommendation:
---------------------------------------
The recommended AME configuration for this workload is to configure the LPAR
with a memory size of 66.50 GB and to configure a memory expansion factor
of 2.17.  This will result in a memory gain of 117%. With this 
configuration, the estimated CPU usage due to AME is approximately 0.14 
physical processors, and the estimated overall peak CPU resource required for
the LPAR is 1.01 physical processors.
 
NOTE: amepat's recommendations are based on the workload's utilization level
during the monitored period. If there is a change in the workload's utilization
level or a change in workload itself, amepat should be run again.
 
The modeled Active Memory Expansion CPU usage reported by amepat is just an 
estimate.  The actual CPU usage used for Active Memory Expansion may be lower 
or higher depending on the workload.
aix09 #

The sample output here was only produced over a short period of time and is therefore not meaningful. The decisive factor is the selection of the time to start amepat and the duration of the run. A representative statement can only be made if the period was long enough and typical peak loads occurred during the observation period.

Note: Particular caution is required with cluster systems. In the event of an error, a cluster node may have to take over resource groups from other cluster nodes. This is typically taken into account when configuring the main memory size. It is therefore best to run amepat when the resource groups to failover are currently running on the system.