Derivation: PAGE FRAME SIZE
PAGEFRAMESIZE
specifies the preferred page frame size in virtual storage for HEAP,
ANYHEAP, and STACK storage that is obtained during application initialization
and runtime.
The default value for non-CICS applications is
PAGEFRAMESIZE(4K,4K,4K).
PAGEFRAMESIZE is ignored under CICS®.
Syntax
.-4K--------------.
>>-PAGeframesize--(--+-----------------+--,--------------------->
'-heap_frame_size-'
.-4K-----------------. .-4K---------------.
>--+--------------------+--,--+------------------+--)----------><
'-anyheap_frame_size-' '-stack_frame_size-'
- heap_frame_size
- Specifies the preferred page frame size in virtual storage for
initial heap storage allocation and any subsequent heap increments.
The page frame size can be specified as one of the following values:
- 4K
- Requests the default value of 4-KB pages.
- 1M
- Requests that 1-MB large pages be used, if available.
- anyheap_frame_size
- Specifies the preferred page frame size in virtual storage for
initial anywhere heap storage allocation and any subsequent anywhere
heap increments. The page frame size can be specified as one of the
following values:
- 4K
- Requests the default value of 4-KB pages.
- 1M
- Requests that 1-MB large pages be used, if available.
- stack_frame_size
- Specifies the preferred page frame size in virtual storage for
initial stack storage allocation and any subsequent stack increments.
The page frame size can be specified as one of the following values:
- 4K
- Requests the default value of 4-KB pages.
- 1M
- Requests that 1-MB large pages be used, if available.
Usage notes
- You cannot set PAGEFRAMESIZE at the system level or
region level.
- You cannot specify PAGEFRAMESIZE with the CEEBXITA assembler user
exit interface.
- In an XPLINK environment, the stack_frame_size suboption
only applies to the upward-growing stack.
- If 1-MB page frames are not available, the default 4-KB page frame
size will be used. No message is issued to indicate this behavior.
- Page frame sizes larger than 4 KB are not allowed below the 16-MB
line. If a PAGEFRAMESIZE parameter specifies 1 MB but that storage
type is allocated below the 16-MB line, then the default 4-KB page
frames is used. No message is issued to indicate this behavior; however,
the runtime options report will show the value that was specified.
- If any PAGEFRAMESIZE parameter specifies 1M, then all of the storage
preallocated to the enclave will request 1-MB page frames. The previous
two usage notes apply as well.
- By default, THREADSTACK storage comes from the library heap storage
that is allocated with the ANYHEAP runtime option. To use 1-MB page
frames for the THREADSTACK, ensure the anyheap_frame_size suboption
specifies 1M.
- When running in a preinitialized environment with an @GETSTORE
service routine, a flag is passed to indicate that storage was requested
to be backed by 1-MB page frames. For more information about using
1-MB page frames with an @GETSTORE service routine, see z/OS Language Environment Programming Guide.
Performance considerations
Large pages
are a special-purpose feature to improve performance; therefore, using
large pages is not recommended for all types of workloads. For more
information about large pages, see the following publications: