IBM Power 780, Технический обзор и введение

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Chapter 3. Virtualization
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3.4.6 Active Memory Sharing
Active Memory Sharing is an IBM PowerVM advanced memory virtualization technology that
provides system memory virtualization capabilities to IBM Power Systems, allowing multiple
partitions to share a common pool of physical memory.
Active Memory Sharing is available only with the Enterprise version of PowerVM.
The physical memory of an IBM Power System can be assigned to multiple partitions in either
dedicated or shared mode. The system administrator has the capability to assign some
physical memory to a partition and some physical memory to a pool that is shared by other
partitions. A single partition can have either dedicated or shared memory:
򐂰 With a pure dedicated memory model, the system administrator’s task is to optimize
available memory distribution among partitions. When a partition suffers degradation
because of memory constraints and other partitions have unused memory, the
administrator can manually issue a dynamic memory reconfiguration.
򐂰 With a shared memory model, the system automatically decides the optimal distribution of
the physical memory to partitions and adjusts the memory assignment based on partition
load. The administrator reserves physical memory for the shared memory pool, assigns
partitions to the pool, and provides access limits to the pool.
Active Memory Sharing can be used to increase memory utilization on the system either by
decreasing the global memory requirement or by allowing the creation of additional partitions
on an existing system. Active Memory Sharing can be used in parallel with Active Memory
Expansion on a system running a mixed workload of several operating system. For example,
AIX partitions can take advantage of Active Memory Expansion. Other operating systems
take advantage of Active Memory Sharing also.
For additional information regarding Active Memory Sharing, see PowerVM Virtualization
Active Memory Sharing, REDP-4470.
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 behavior might lead to a shortage of the available memory resources, forcing
paging by the Active Memory Sharing partition operating systems, the Active Memory
Deduplication pool, or both, which might decrease overall system performance.
Figure 3-13 shows the standard behavior of a system without Active Memory Deduplication
enabled on its Active Memory Sharing (shown as AMS in the figure) shared memory pool.