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IBM Power 720 and 740 Technical Overview and Introduction
Figure 3-15 shows two pages being written in the Active Memory Sharing 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 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 LPARs 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 to 1/256 of the configured maximum Active Memory Sharing memory pool size.
Having this table be 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 through a managed
console, allowing administrators to take the following steps:
Enable and disable Active Memory Deduplication at an Active Memory Sharing 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
Sig
nat
ure
Fun
ctio
n
Signature of Page A being written
on the Deduplication Table
Signature of Page B matching
Sign A on the Deduplication Table
