z/VM: CP Commands and Utilities Reference - z/VM - IBM

SET RESERVED
SET RESERVED
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Set
Authorization
Purpose
REServed
Operands
Usage Notes
userid
*
nn
OFF
Privilege Class: A
1370 z/VM: CP Commands and Utilities Reference
Use SET RESERVED to establish the number of real storage pages available to a
specified virtual machine.
userid
*
identifies the virtual machine for which you want to establish the reserved page
performance option. To specify your own virtual machine, enter an asterisk (*).
nn
OFF
is the number of pages that the user is entitled to have resident in real storage
at all times. Normal system stealing procedures may take any resident private
page in any private address space owned by the user’s virtual machine, down
to the number of pages that are reserved (nn). Unlike the CP LOCK command,
there is no guarantee that a specific resident page will remain resident. While
the number of resident pages in a virtual machine is less than or equal to nn,
normal system steal procedures will not affect it.
The maximum number of pages that you can reserve is limited by the number
of private addressable pages in all private address spaces owned by the user’s
virtual machine.
Specify OFF to reset to zero the number of pages reserved for the specified
user.
1. Although you can enable the reserved-page performance option for more than
one user, you should use the SET RESERVED command sparingly, because
system performance can diminish.
2. The user should be in CP mode if the full syntax for SET RESERVED is used.
3. CP maintains a count of the total number of pages allowed to be reserved due
to SET RESERVED commands.
When a SET RESERVED command is issued, if the command is increasing the
reserved limit for the user then the new total is compared to the current
pageable DPA (dynamic paging area). If the new total exceeds the pageable
DPA, a message is issued and the user’s reserved pages value is not changed.
If the command is decreasing the reserved limit for the user and the new total is
above the current pageable DPA, the command succeeds but the message is
still issued as a warning that the reserved limit is set too high.
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