Adaptive Address Space Whitepaper

alternatives to
Reasons for not using the MPAS layout could include:
MPAS
1. Application is targeted for the PA-RISC architecture.
2. Application is targeted for a version of HP-UX preceding HP-UX 11i V2.
3. Application vendor wants to retain performance advantages provided
to non-MPAS applications.
Applications that cannot use MPAS can get some of the advantages that
MPAS layouts provide by choosing one of several address space layouts
provided by HP-UX as described earlier.
Limitation number 3 in the section “limitations of traditional HP-UX address
space models” can be addressed by using the memory-windows functionality.
performance
Using MPAS layouts may incur costs in terms of performance. The performance
cost comes mainly from using aliases. This performance cost becomes a factor
if the application has a large amount of data that is shared between
processes.
On the other hand, 32-bit processes using MPAS layouts gain the advantage of
a flexible virtual address space. This flexibility translates to a performance
advantage to processes that can use larger address space to do more work,
faster. For example, the Java Virtual Machine is very sensitive to the amount of
heap space it has. Since MPAS allows processes to have up to 4GB of address
space for the heap, this can translate to a performance advantage.
The performance difference thus seen will vary from application to application.
The following factors can aid in deciding whether or not to use the feature. In
terms of performance, MPAS should be a good alternative for:
o processes whose performance is sensitive to the amount of private data
space available.
o processes that do a lot of mprotect(2) operations on shared data
MPAS could lower performance for applications that:
o share a lot of data between processes
compatibility/
AAS provides binary and API compatibility for applications that do not use the
feature.
interoperability
configuration
An application that wants to use MPAS layouts needs to link with a special flag.
Details are mentioned in the section “how to get MPAS?”
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