Specifications

5102ch03.fm Draft Document for Review May 12, 2014 12:46 pm
96 IBM Power System S822 Technical Overview and Introduction
Active Memory Deduplication allows the POWER Hypervisor to dynamically map identical
partition memory pages to a single physical memory page within a shared memory pool. This
way enables a better utilization of the Active Memory Sharing shared memory pool,
increasing the system’s overall performance by avoiding paging. Deduplication can cause the
hardware to incur fewer cache misses, which also leads to improved performance.
Active Memory Deduplication depends on the Active Memory Sharing feature to be available,
and consumes CPU cycles donated by the Active Memory Sharing pool’s Virtual I/O Server
(VIOS) partitions to identify deduplicated pages. The operating systems that are running on
the Active Memory Sharing partitions can “hint” to the POWER Hypervisor that some pages
(such as frequently referenced read-only code pages) are particularly good for deduplication.
To perform deduplication, the hypervisor cannot compare every memory page in the Active
Memory Sharing pool with every other page. Instead, it computes a small signature for each
page that it visits and stores the signatures in an internal table. Each time that a page is
inspected, a look-up of its signature is done in the known signatures in the table. If a match is
found, the memory pages are compared to be sure that the pages are really duplicates. When
a duplicate is found, the hypervisor remaps the partition memory to the existing memory page
and returns the duplicate page to the Active Memory Sharing pool.
From the LPAR perspective, the Active Memory Deduplication feature is completely
transparent. If an LPAR attempts to modify a deduplicated page, the hypervisor grabs a free
page from the Active Memory Sharing pool, copies the duplicate page contents into the new
page, and maps the LPAR’s reference to the new page so that the LPAR can modify its own
unique page.
For additional information regarding Active Memory Dedupliation, see Power Systems
Memory Deduplication, REDP-4827.
3.4.8 Operating system support for PowerVM
At the time of writing all PowerVM features are supported by the operating systems
compatible with the POWER8 servers, except the Active Memory Expansion which is not
supported with Linux.
Table 3-4 summarizes the PowerVM features that are supported by the operating systems
compatible with the POWER8 processor-based servers.
Table 3-4 Virtualization features supported by AIX, and Linux
Feature AIX 6.1 TL8 AIX 7.1 RHEL 6.5 SLES 11 SP3
Virtual SCSI Yes Yes Yes Yes
Virtual Ethernet Yes Yes Yes Yes
Shared Ethernet Adapter Yes Yes Yes Yes
Virtual Fibre Channel Yes Yes Yes Yes
Virtual Tape Yes Yes Yes Yes
Logical partitioning Yes Yes Yes Yes
DLPAR I/O adapter add/remove Yes Yes Yes Yes
DLPAR processor add/remove Yes Yes Yes Yes
DLPAR memory add Yes Yes Yes Yes