Derivation: STACK storage for AMODE 64

STACK64 controls the allocation of the thread's stack storage for AMODE 64 applications.

AMODE 64 default

STACK64=((1M,1M,128M),OVR)

Syntax

>>-STACK64--=--(--(--initial--,--increment--,--maximum--)--,---->

   .-OVR----.      
>--+-NONOVR-+--)-----------------------------------------------><

initial

Determines the size of the initial stack segment. The storage is contiguous. This value is specified as nM bytes of storage.

increment

Determines the minimum size of any subsequent increment to the downward-growing stack area. This value is specified as nM bytes of storage. The actual amount of allocated storage is the larger of two values— increment or the requested size—rounded up to the nearest 1MB.

If you specify increment as 0, only the amount of the storage needed at the time of the request, rounded up to the nearest multiple of 1MB, is obtained.

The requested size is the amount of storage a routine needs for a stack frame.

maximum

Specifies the maximum stack size. This value is specified as nM bytes of storage. When the maximum size is less than the initial size, initial is used as the maximum stack size.

OVR

Specifies that the option can be overridden.

NONOVR

Specifies that the option cannot be overridden.

Usage notes

• The 1 MB guard area is not included in any of the sizes.
• The maximum stack segment is the maximum of STACK64 initial and maximum sizes.
• When a multithreaded application that creates many pthreads is run, the default value of 128MB for the maximum stack size of the STACK64 and THREADSTACK64 runtime options might cause excessive use of system resources, such as real storage. For such applications, you need to use the Language Environment® Storage Report (RPTSTG runtime option) to determine the actual pthread stack storage usage of your application, and then use the THREADSTACK64 runtime option to set the maximum stack size to a value closer to the actual usage.

Performance considerations

To improve performance, use the storage report numbers generated by the RPTSTG runtime option as an aid in setting the initial and increment sizes for STACK64.

For more information

• See RPTSTG for more information about the RPTSTG runtime option.
• For more information about using the storage reports generated by the RPTSTG runtime option to tune the stacks for AMODE 64 applications, see z/OS Language Environment Programming Guide for 64-bit Virtual Addressing Mode.