Chapter 3. Virtualization
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3.3 Active Memory Expansion
Active Memory Expansion is a optional feature for the enterprise servers Power E870 and
Power E880.
This feature enables memory expansion on the system. By using compression and
decompression of memory, content can effectively expand the maximum memory capacity,
providing additional server workload capacity and performance.
Active Memory Expansion is a technology that allows the effective maximum memory
capacity to be much larger than the true physical memory maximum. Compression and
decompression of memory content can allow memory expansion up to 125% for AIX
partitions, which in turn enables a partition to perform more work or support more users with
the same physical amount of memory. Similarly, it can allow a server to run more partitions
and do more work for the same physical amount of memory.
Active Memory Expansion uses the CPU resource of a partition to compress and decompress
the memory contents of this same partition. The trade-off of memory capacity for processor
cycles can be an excellent choice, but the degree of expansion varies based on how
compressible the memory content is, and it also depends on having adequate spare CPU
capacity available for this compression and decompression.
The POWER8 processor includes Active Memory Expansion on the processor chip to provide
dramatic improvement in performance and greater processor efficiency. To take advantage of
the hardware compression offload, AIX 6.1 Technology Level 9 or later is required.
Tests in IBM laboratories, using sample work loads, showed excellent results for many
workloads in terms of memory expansion per additional CPU used. Other test workloads had
more modest results. The ideal scenario is when there are many cold pages, that is,
infrequently referenced pages. However, if many memory pages are referenced frequently,
Active Memory Expansion might not be a preferred choice.
64-core and
128-thread scaling
32-core and
128-thread scaling
64-core and
256-thread scaling
128-core and
512-thread scaling
256-core and
1024-thread
scaling
1024-thread
Scaling
Hybrid threads
Transactional
memory
Active system
optimization
hardware assists
Performance and
scalability for large
scale-up single system
image workloads
(such as OLTP, ERP
scale-up, and WPAR
consolidation)
EnergyScale CPU Idle
EnergyScale CPU Idle
and Folding with NAP
and SLEEP
WINKLE, NAP, SLEEP,
and Idle power saver
Improved energy
efficiency
POWER6 and
mode
POWER7 mode
POWER8 mode
Customer value
Note: The Active Memory Expansion feature is not supported by IBM i and the Linux
operating system.
Tip: If the workload is based on Java, the garbage collector must be tuned so that it does
not access the memory pages so often, that is, turning cold pages to hot.
