Power 7 - Active Memory Expansion

Active Memory Expansion (AME)

Introduction:

IBM’s POWER7™ systems with AIX® feature Active Memory™ Expansion, a new technology for expanding a system’s effective memory capacity. Active Memory Expansion employs memory compression technology to transparently compress in-memory data, allowing more data to be placed into memory and thus expanding the memory capacity of POWER7 systems. Utilizing Active Memory Expansion can improve system utilization and increase a system’s throughput.

Active Memory Expansion Overview:

Active Memory Expansion relies on compression of in-memory data to increase the amount of data that can be placed into memory and thus expand the effective memory capacity of a POWER7 system. The in-memory data compression is managed by the operating system, and this compression is transparent to applications and users.

Active Memory Expansion is configurable on a per-logical partition (LPAR) basis. Thus, Active Memory Expansion can be selectively enabled for one or more LPAR’s on a system.

When Active Memory Expansion is enabled for a LPAR, the operating system will compress a portion of the LPAR’s memory and leave the remaining portion of memory uncompressed. This results in memory effectively being broken up into two pools – a compressed pool and an uncompressed pool. The operating system will dynamically vary the amount of memory that is compressed based on the workload and the configuration of the LPAR.

The operating system will move data between the compressed and uncompressed memory pools based on the memory access patterns of applications. When an application needs to access data that is compressed, the operating system will automatically decompress the data and move it from the compressed pool to the uncompressed pool, making it available to the application. When the uncompressed pool is full, the operating system will compress data and move it from the uncompressed pool to the compressed pool. This compression and decompression activity is transparent to the application.

Because Active Memory Expansion relies on memory compression, some additional CPU utilization will be consumed when Active Memory Expansion is in-use. The amount of additional CPU utilization needed for Active Memory Expansion will vary based on the workload and the level of memory expansion being used.

System Requirements:

Active Memory Expansion is supported across all POWER7 systems. In order to use Active Memory Expansion, the following minimum levels of software are required:

• HMC: V7R7.1.0.0
• eFW: 7.1
• AIX: 6.1 TL4 SP2