Specifications

Chapter 3. Virtualization 125
sample work loads, showed excellent results for many workloads in terms of memory
expansion per additional CPU utilized. Other test workloads had more modest results.
Clients have much control over Active Memory Expansion usage. Each individual AIX
partition can turn on or turn off Active Memory Expansion. Control parameters set the amount
of expansion desired in each partition to help control the amount of CPU used by the Active
Memory Expansion function. An initial program load (IPL) is required for the specific partition
that is turning memory expansion on or off. After turned on, monitoring capabilities are
available in standard AIX performance tools, such as lparstat, vmstat, topas, and svmon.
Figure 3-3 represents the percentage of CPU that is used to compress memory for two
partitions with separate profiles. The green curve corresponds to a partition that has spare
processing power capacity. The blue curve corresponds to a partition constrained in
processing power.
Figure 3-3 CPU usage versus memory expansion effectiveness
Both cases show that there is a knee-of-curve relationship for CPU resource required for
memory expansion:
򐂰 Busy processor cores do not have resources to spare for expansion.
򐂰 The more memory expansion done, the more CPU resource required.
The knee varies depending on how compressible that the memory contents are. This
example demonstrates the need for a case-by-case study of whether memory expansion can
provide a positive return on investment.
% CPU
utilization
for
expansion
Amount of memory expansion
1 = Plenty of spare
CPU resource
available
2 = Constrained
CPU resource –
already running at
significant utilization
1
2
Very cost effective