POWERVM - AME, AMS

Active Memory Expansion

Active Memory Expansion is the ability to expand the memory available to an AIX partition beyond the amount of assigned physical memory. Active Memory Expansion compresses memory pages to provide additional memory capacity for a partition. (It is a Power7 feature.)

AIX is currently the only opreating system that supports AME.

Planning considerations:
- Data that is already compressed will not compressed further with AME
- workloads that tend to frequently access only a small portion of memory will perform best with AME
- Active Memory Expansion will not compress file pages that are cached in memory
- Active Memory Expansion will not compress pinned virtual memory pages


AME config:
1. amepat <min>                <--run during peak times, i.e. amepat 120 will run for 2 hours and it will suggest an expansion factor
2. HMC -> profile -> memory        <--here the Act. Mem. Expansion factor should be ticked and the value entered
3. Partition Deactivate - Activate
4. lparstat -i                <--it will show the settings (once it has been enabled, the valuse can be changed dynamically (DLPAR))

Later if you want more fine tuning you can run 'amepat <min>' again.


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Active Memory Sharing

Active Memory Sharing (AMS) enables the sharing of a pool of physical memory among partitions on a single IBM Power Systems server Power 6 or later, helping to increase memory utilization and drive down system costs.

The memory is dynamically allocated amongst the partitions as needed, to optimize the overall physical memory usage in the pool. Instead of assigning a dedicated amount of physical memory to each logical partition, the POWER Hypervisor constantly provides the physical memory from the Shared Memory Pool as needed.

Logical memory:
Quantity of memory that the operating system manages and can access. Logical memory pages that are in use may be backed up by either physical memory or a pool’s paging device.

For example, four logical partitions with 10 GB of dedicated memory each can be configured to share a memory pool of 40 GB, each with 15 GB of logical memory assigned.


Paging:
A Paging Virtual I/O Server is a partition that provides paging services for a shared memory pool and manages the paging spaces for shared memory partitions associated with a shared memory pool. A Virtual I/O Server enabled as a Paging Virtual I/O Server is designed to serve one shared memory pool.

This new configuration does not change the global memory requirements, and every logical partition can have the same amount of physical memory it had before. However, memory allocation is highly improved since an unexpected memory demand due to unplanned peak of one logical partition can be satisfied by the shared pool. In deed unused memory pages from shared-memory partitions can be automatically assigned to the more demanding one automatically

The hypervisor has to use a paging device to back up the excess memory that it cannot back up using the physical memory.

A paging device is required for each shared memory partition. The size of the paging device must be equal to or larger than the maximum logical memory defined in the partition profile. The paging devices are owned by a Virtual I/O Server. A paging device can be a logical volume or a whole physical disk. Disks can be local or provided by an external storage subsystem through a SAN.

Reserved storage device pool will be created automatically if AMS will be used, it will need for shared memory paging device.
(Ensure that PVIDs for paging devices for physical volumes set up by the HMC are cleared before use.)

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A Virtual Asynchronous Service Interface (VASI) is a virtual device that allows communications between the Virtual I/O Server and the hypervisor. In AMS environment, this device is used for handling hypervisor paging activity.

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