Kernel-Managed Swap Facility (KMSF) Manual

Configuring KMSF
Kernel-Managed Swap Facility (KMSF) Manual—425824-005
2-3
Amount of Swap Space to Allocate
Configuration Guidelines
Follow these guidelines in planning your configuration:
•
In general, systems used for application development require more swap space
than systems running applications in a production environment because
application development tools often require more swap space.
•
The amount of swap space you need to configure for a processor is based on the
peak load, where load is defined as the amount of swapable memory pages. (Not
all memory pages are swapable.) In most cases, the amount of swap space to
configure is a multiple of the physical memory size. The actual requirement scales
with the number of processes you run. The load is based on the following:
•
The total number of processes.
•
The amount of memory a process uses in addition to the minimum required.
For example, if the program allocates segments on its own beyond the
minimum requirement, then you need to increase the swap space.
•
If you create additional processes, you might need to allocate additional swap
space and monitor it frequently to ensure that you have sufficient space.
•
Increasing the physical memory might not reduce your swap space requirements.
For example, if you increase the physical memory to increase system performance
by allowing you to run more processes, those additional processes might require
KMSF swap space.
•
On large systems, consider dedicating entire disks to be used for KMS files.
•
In general, systems running H-series RVUs require more KMS space for each
processor than systems running G-series RVUs:
°
Processors in systems running H-series RVUs have significantly better
performance than processors in systems running G-series RVUs, allowing a
greater number of processes to be run in each processor.
°
Because of differences in the data mapping and data alignment requirements
of the processor, data allocated from heaps or pools has grown in size.
°
Because of the difference in processor architecture and its software calling
conventions, the amount of stack space needed on a per process basis has
grown.
°
The way the compilers are invoked by the application developer has a greater
impact on the size of the applications data space requirements on systems
running H-series RVUs than they do on systems running G-series RVUs. For
example, both the epTAL and the C compilers have compile-time directives for
the level of code (and data) optimization that the programmer is requesting as
part of this compile step. When a module is compiled at the lowest level of
optimization it typically uses much more stack space than when the same
module is compiled at the highest level of optimization.