Specifications

144 IBM Power 770 and 780 Technical Overview and Introduction
3.4.7 Active Memory Deduplication
In a virtualized environment, the systems might have a considerable amount of
duplicated information stored on RAM after each partition has its own operating system,
and some of them might even share the same kind of applications. On heavily loaded
systems this might lead to a shortage of the available memory resources, forcing paging by
the AMS partition operating systems, the AMD pool, or both, which might decrease overall
system performance.
Figure 3-13 shows the standard behavior of a system without Active Memory Deduplication
(AMD) enabled on its AMS shared memory pool. Identical pages within the same or different
LPARs each require their own unique physical memory page, consuming space with
repeated information.
Figure 3-13 AMS shared memory pool without AMD enabled
Active Memory Deduplication allows the hypervisor to dynamically map identical partition
memory pages to a single physical memory page within a shared memory pool. This enables
a better utilization of the AMS shared memory pool, increasing the system’s overall
performance by avoiding paging. Deduplication can cause the hardware to incur fewer cache
misses, which will also lead to improved performance.
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Without
Active Memory
Deduplication
Mappings
AMS shared memory pool
LPAR1
Logical Memory
LPAR2
Logical Memory
LPAR3
Logical Memory
D
U
Duplicate pages
Unique pages
KEY: