All computers have a limited amount of random access memory (RAM) in which to run programs. Therefore, one of the perennial design issues for all computer systems is how to make the best use of the entire RAM that is physically available in the system, in order to run as many programs concurrently as possible, in the limited space available.
Active Memory Expansion, originally a POWER7 feature, supplies a new technique for making better use of RAM: Portions of programs that are infrequently used are compressed into a smaller space in RAM. This, in turn, expands the amount of RAM available for the same or other programs. Starting with POWER7+, Active Memory Expansion memory page compression and decompression is offloaded to a hardware accelerator.
This white paper describes the process of Active Memory Expansion in more detail in the next sections, and then reports measurements on a typical workload which illustrates the beneficial effects. Among the benefits of Active Memory Expansion, this paper shows the following scenarios and their performance results:
- Reducing the physical memory requirement of an logical partition (LPAR) resulting in 125% memory expansion on a POWER7+ system
- Increasing the effective memory capacity and throughput of a memory-constrained LPAR, resulting in a 54% increase in application throughput on a POWER7+ system