Specifications

146 IBM Power 770 and 780 Technical Overview and Introduction
Figure 3-15 shows two pages being written in the AMS memory pool and having their
signatures matched on the deduplication table.
Figure 3-15 Memory pages having their signatures matched by Active Memory Deduplication
From the LPAR point of view, the AMD feature is completely transparent. If an LPAR attempts
to modify a deduplicated page, the hypervisor grabs a free page from the AMS 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.
System administrators can dynamically configure the size of the deduplication table, ranging
from 1/8192 up to 1/256 of the configured maximum AMS memory pool size. Having this table
too small might lead to missed deduplication opportunities. Conversely, having a table that is
too large might waste a small amount of overhead space.
The management of the Active Memory Deduplication feature is done via managed console,
allowing administrators to take the following steps:
򐂰 Enable and disable Active Memory Deduplication at an AMS Pool level.
򐂰 Display deduplication metrics.
򐂰 Display and modify the deduplication table size.
AMS
Memory
Pool
Page A
Dedup
Table
Sign A
Signature
Function
AMS
Memory
Pool
Page A
Dedup
Table
Sign A
Signature
Function
Page B
S
i
g
n
a
t
u
r
e
F
u
n
c
t
i
o
n
Signature of Page A being written
on the Deduplication Table
Signature of Page B matching
Sign A on the Deduplication Table