Paging files and paging area
Paging memory is required to provide virtual address space, and this is implemented using paging files. Paging files always have the name SYS.PAGING.<vsn>.
To permit it to be used for paging, a created paging file must be assigned explicitly to the paging memory.
The sum of the paging files in the system which are assigned to the paging memory is called a paging area.
The paging area can be dynamically extended or reduced while the system is running by assigning paging files to the paging area or releasing them from it. A particular size and structure of the paging area is a prerequisite during system initialization (see "Selecting the paging area at startup").
The virtual address space available for a session is determined by the size of the paging area because one block (two 2K PAM pages) must exist in the paging area for each virtual page. The maximum overall size of the paging area is 4 TB.
During system initialization, the parameter service can be used to select the files that are to be used in the subsequent session from the set of the created and available paging files (see section "Selection of the paging area at startup (PAGING)").
Consequently a distinction must be made between initializing paging files (including reserving memory space) and selecting paging files for the session.
General conditions for a paging file:
It may not be a file >= 32 GB
It may not be configured on a private disk
It may not be configured on a shared pubset
Paging disk and paging pubset
A disk is called a paging disk when a paging file has not only been initialized there, but has also been assigned to the paging memory.
As a general rule, any disk type is permissible. The disks of the paging area need not be of the same type.
A paging file may be located on a disk which was created dynamically as a DRV volume. (Paging files which were specified in the parameter file – PAGING parameter record – during system initialization and are not located in the home pubset are not supported by DRV.) However, only one of the two disks is written to.
A pubset is referred to as a paging pubset when at least one disk of the pubset is used as a paging disk.
If a pubset contains only paging files, it is a pure paging pubset. If a pubset is not a pure paging pubset and consists of multiple disks, no paging file should be created on its pubres.
It is recommended that the paging area be implemented predominantly using single-disk pubsets since this simplifies the reconfiguration of the paging area during operation when a paging file is included.
Command | Meaning |
CREATE-PAGING-FILE | Create paging file |
DELETE-PAGING-FILE | Delete paging file (overwrite with binary zeros) |
EXTEND-PAGING-AREA | Dynamically extend paging area |
MODIFY-PAGING-AREA-ATTRIBUTES | Modify attributes of paging files on disk |
REDUCE-PAGING-AREA | Reduce paging area |
SHOW-PAGING-CONFIGURATION | Display information on used and unused paging files |
Table 8: Overview of commands for paging areas
The SHOW-PAGING-CONFIGURATION command outputs the following information:
Which paging files are used
Which paging files (on imported pubsets) are unused
Whether a volume contains a used or unused paging file
The overall size of the used/unused paging files which were found
Examples of the output for the paging files
/SHOW-PAGING-CONFIGURATION VOLUME=*UNUSED,INFORMATION=*ALL
% LIST OF THE FOUND AND UNUSED PAGING-FILES :
%
% VOLUME CAT-ID SIZE RESTRICTION
% 1OSH.0 1OSH 256.00 MB NONE
% 1OSH.2 1OSH 256.00 MB NONE
% -----------------------------------------------------------------------
% SUMMARY 512.00 MB
/SHOW-PAGING-CONFIGURATION VOLUME=*USED,INFORMATION=*ALL
% LIST OF THE USED PAGING-FILES :
%
% VOLUME CAT-ID SIZE FREESIZE UTILIZATION REDUCTION R
% 1OP1.1 * 1OP1 2500.00 MB 1510.99 MB *LOW *NOT-REQ N
% 1OP1.0 * 1OP1 2500.00 MB 2200.00 MB *LOW *NOT-REQ N
% 1OPP.0 * 1OPP 2500.00 MB 395.90 MB *LOW *NOT-REQ N
% 1OSH.1 1OSH 256.00 MB 200.00 MB *LOW *NOT-REQ N
% -----------------------------------------------------------------------
% SUMMARY 7756.01 MB
%
% EMM2317 THE SIZE OF VOLUME(S) - MARKED WITH * - IS INCREASED BY 25%,
BECAUSE THE PAM-KEYS ARE USED AS PAGING-AREA