Active Memory Expansion - IBM Power7 Optimization And Tuning Manual

If a pair of LPARs is created with the intent of one being a failover to another partition, and
one partition fails, the other partition (which is placed in the same node, if both are in the
same affinity group) uses all of the resources that were freed up from the failed LPAR.
The following HMC CLI command adds or removes a partition from an affinity group:
chsyscfg -r prof -m <
lpar_name=<
group_id is a number 1 - 255 (255 groups can be defined), and affinity_group_id=none
removes a partition from the group.
When the hypervisor places resources at frame reboot, it first places all the LPARs in group
255, then the LPARs in group 254, and so on. Place the most important partitions regarding
affinity in the highest configured group.
PowerVM resource consumption for capacity planning considerations
PowerVM hypervisor consumes a portion of the memory resources in the system. During
your planning stage, consider the layout of LPARs. Factors that affect the amount of memory
that is consumed are the size of the hardware page tables in the partitions, HEA resources,
HCA resources, the number of I/O devices, hypervisor memory mirroring, and other factors.
Use the IBM System Planning Tool (available at
http://www.ibm.com/systems/support/tools/systemplanningtool/) to estimate the amount
of memory that is reserved by the hypervisor.
Licensing resources and Capacity Upgrade on Demand (CUoD)
Power Systems support capacity on demand so that customers can license capacity on
demand as business needs for compute capacity grows. Therefore, a Power System might
not have all resources that are licensed, which poses a challenge to allocate both cores and
memory from a local domain. PowerVM (eFW 7.3 level firmware) correlates customer
configurations and licensed resources to allocated cores and memory from the local domain
to each of the LPARs. During a CEC reboot, the hypervisor places all defined partitions as
optimally as possible and then unlicenses the unused resources.
For more information about this topic, see 3.3, "Related publications" on page 65.

3.2.4 Active memory expansion

Active memory expansion (AME) is a capability that is supported on POWER7 and later
servers that employs memory compression technology to expand the effective memory
capacity of an LPAR. The operating system identifies the least frequently used memory pages
and compresses them. The result is that more memory capacity within the LPAR is available
to sustain more load, or the ability to remove memory from the LPAR to be used to deploy
more LPARs. The POWER7+ processor provides enhanced support of AME with the
inclusion of on-chip accelerators onto which the work of compression and decompression
is offloaded.
AME is deployed by first using the amepat tool to model the projected expansion factor and
CPU usage of a workload. This modeling looks at the compressibility of the data, the memory
reference patterns, and current CPU usage of the workload. AME can then be enabled for the
LPAR by setting the expansion factor. The operating system then reports the physical
memory available to applications as
transparently, the operating system locates and compresses cold pages to maintain the
appearance of expanded memory.
64
POWER7 and POWER7+ Optimization and Tuning Guide
system_name
partition_name
>,affinity_group_id=<
actual memory
profile_name
> -i name=<
group_id
>
times the
>
expansion factor . Then,