pa_maxssiz(5)

NAME

pa_maxssiz: pa_maxssiz_32bit, pa_maxssiz_64bit — maximum size (in bytes) of the stack for a user process running under the PA-RISC emulator on an Integrity system

VALUES

Default

32 bit default: 0x04FC6000 (79Mb)

64 bit default: 0x20000000 (512Mb)

Allowed values

32 bit minimum: 0x04FC6000 (79Mb)

32 bit maximum: 0x1BF00000 (447Mb)

64 bit minimum: 0x20000000 (512Mb)

64 bit maximum: 0xA0000000 (2.5Gb)

DESCRIPTION

User programs on HP-UX systems are composed of five discrete segments of virtual memory: text (or code), data, stack, shared, and I/O.

PA-RISC binaries running under Itanium-based system using the PA-RISC emulator have their stack segment size (which includes both the memory stack and the RSE stack) determined by pa_maxssiz_32bit or pa_maxssiz_64bit.

The emulated stack from the process perspective is the same as the stack if the process were executed on a PA-RISC machine without the emulator. The actual (non-emulated) process stack (both memory and RSE) for an emulated process are of a non-configurable size and are used solely for the internal use of the emulator for a PA-RISC process on Itanium-based system. This tunable therefore represents the required value of maxssiz or maxssiz_64bit on a corresponding PA-RISC machine to execute the emulated process plus working space for the emulator itself.

As with the stack address space sized by maxssiz, the address space used by the emulator is both private to the process and not usable for other purposes regardless of whether the emulator stack grows to encompass the full range or not. As a consequence, the tunable value may be viewed as an amount of process data address space which will be unavailable to this PA-RISC process. Caution is advised especially for 32 bit processes since the default address space model only provides 1 Gb of private data space. Setting this tunable too high will result in execution failure when other allocations (private mmap() calls or sbrk() calls) fail due to insufficient available address space. If this occurs, revise the address space model of the failing PA-RISC executable using chatr to allow more private data virtual address space or lower the tunable.

Who is Expected to Change This Tunable?

Anyone.

Restrictions on Changing

Changes to this tunable only take effect after a reboot of the system.

Given that the user memory stack size is not modifiable by this tunable, it is expected that detailed knowledge of the PA-RISC emulator memory usage is needed before modifying this tunable.

When Should the Value of This Tunable Be Raised?

This tunable should be raised if the PA-RISC emulator on Itanium-based system requires additional space for stack emulation.

What Are the Side Effects of Raising the Value?

The PA-RISC emulator will use more of the virtual address space for stack, leaving less virtual address space for data allocations. Raising the value too high will result in application failure when data allocations fail due to insufficient virtual address space.

Since it may not be known which processes are based off of PA-RISC binaries and which off Itanium-based binaries, arbitrary raising of this tunable is discouraged.

When Should the Value of This Tunable Be Lowered?

This tunable should only be lowered if the workload for the PA-RISC emulator is known on the system, more space than is needed is currently used for stack emulation, and swap space (either reserved or allocated) is at a premium on the system.

What Are the Side Effects of Lowering the Value?

Lowering this tunable will decrease the available stack space for emulated PA-RISC binary executions. Emulated processes needing larger stacks will fail stack growth requests (just as lowering maxssiz or maxssiz_64bit may cause process termination due to failure to grow stack).

What Other Tunable Values Should Be Changed at the Same Time?

None.

WARNINGS

All HP-UX kernel tunable parameters are release specific. This parameter may be removed or have its meaning changed in future releases of HP-UX.

Installation of optional kernel software, from HP or other vendors, may cause changes to tunable parameter values. After installation, some tunable parameters may no longer be at the default or recommended values. For information about the effects of installation on tunable values, consult the documentation for the kernel software being installed. For information about optional kernel software that was factory installed on your system, see HP-UX Release Notes at http://docs.hp.com.

AUTHOR

pa_maxssiz was developed by HP.