LIBHEAP64 (AMODE 64 only)

The LIBHEAP64 runtime option controls the allocation of heap storage that is used by Language Environment for AMODE 64 applications. Storage that is unrestricted can be located anywhere in 64-bit addressable storage.

The default value for AMODE 64 applications is LIBHEAP64(1M,1M,FREE,16K,8K,FREE,8K,4K,FREE).


Syntax

                                                   .-KEEP-.   
>>-+-LIBHEAP64-+--(--+--------+--,--+--------+--,--+------+----->
   '-LH64------'     '-init64-'     '-incr64-'     '-FREE-'   

                                 .-KEEP-.                     
>--,--+--------+--,--+--------+--+------+--,--+--------+--,----->
      '-init31-'     '-incr31-'  '-FREE-'     '-init24-'      

               .-KEEP-.      
>--+--------+--+------+--)-------------------------------------><
   '-incr24-'  '-FREE-'

init64: Determines the initial allocation of library heap storage that is obtained above the 2G bar. Specify this value as nM bytes of storage. If a value of 0 or less is specified, the default is used.
incr64: Determines the minimum size of any subsequent increment to the library heap storage obtained above the 2G bar. Specify this value as nM bytes of storage. If a value less than 0 is specified, the default is used.
KEEP: Specifies that an increment to library heap storage is not released when the last of the storage within that increment is freed.
FREE: Specifies that an increment to library heap storage is released when the last of the storage within that increment is freed.
init31: Determines the minimum initial size of library heap storage that is obtained above the 16M line and below the 2G bar. This value can be specified as n, nK, or nM number of bytes. If 0 is specified, the initial storage is obtained on the first use and is based on the increment size. The amount of allocated storage is rounded up to the nearest multiple of 8 bytes.
incr31: Determines the minimum size of any subsequent increment to library heap storage that is obtained above the 16M line and below the 2G bar. This value can be specified as n, nK, or nM number of bytes. The amount of allocated storage is rounded up to the nearest multiple of 8 bytes.
init24: Determines the minimum initial size of library heap storage that is obtained below the 16M line. This value can be specified as n, nK, or nM number of bytes. If 0 is specified, the initial storage is obtained on the first use and is based on the increment size. The amount of allocated storage is rounded up to the nearest multiple of 8 bytes.
incr24: Determines the minimum size of any subsequent increment to library heap storage that is obtained below the 16M line. This value can be specified as n, nK, or nM number of bytes. The amount of allocated storage is rounded up to the nearest multiple of 8 bytes.

Performance consideration

You can improve performance with the LIBHEAP64 runtime option by specifying values that minimize the number of times the operating system allocates storage. See RPTSTG for information about how to generate a report you can use to determine the optimum values for the LIBHEAP64 runtime option.

For more information

For more information about heap storage and heap storage tuning with storage report numbers, see z/OS Language Environment Programming Guide.