Adaptive Address Space Whitepaper

Adaptive Address Space
introduction
executive
summary
The Adaptive Address Space (AAS) feature is introduced in HP-UX 11i V2. AAS
provides a new address space layout, MPAS (Mostly Private Address Space),
which helps applications targeted for HP-UX running on Intel® Itanium ®
Processor Family (IPF) machines. MPAS can also be used to aid application
portability to HP-UX.
This paper describes the features AAS provides, how applications can use these
features and impacts thereof.
The memory model traditionally used by HP-UX trades off an application’s
flexibility in using its address space for performance. This means that 32-bit
applications coded for HP-UX that share a lot of data among processes enjoy
certain performance advantages that they would not on other operating
systems. However, these applications are restricted by certain limitations of HP-
UX’s memory model.
AAS removes all such limitations from HP-UX for applications that choose to use
the feature. The removal of these limitations means that applications have
greater control of their own address space and have memory-management
features that did not exist on HP-UX but were provided by several other
operating systems (e.g. Solaris® and Linux®). This aids portability of applications
to HP-UX from these other operating systems. However, this may cause the
application to loose some of the performance advantages typically enjoyed
by HP-UX applications.
Application vendors coding for HP-UX can also use the flexibility and features
offered by AAS to simplify their design.
This applies only to HP-UX applications compiled and linked for IPF platforms.
2