The SYSCOR .acro definition can be found in !AL310 Planning and CP provides three performance options, locked pages, reserved page
fraaes, and a virtual=real area, to reduce the paging requirements of
virtual machines. Generally, these facilities require soae dedication
of real storage to the chosen virtual machine and, therefore, improve its performance at the expense of other virtual .achines. LOCKED PAGES OPTION The LOCK co •• and, which is available to the systea operator (with
privilege class A), can be used to permanently fix or lock specific user
pages of virtual storage into real storage. In so doing, all paging I/O for these page frames is eliminated. Since this facility reduces total real page fraaes) that are available to support other virtual aachines, only
frequently used pages should be locked into real storage. Since page
zero (the first 4096 bytes) of a virtual .achine storage is referred to
and changed frequently (for exaaple, whenever a virtual aachine
interrupt occurs or when a CSW is stored), it should be the first page
of a particular virtual machine that an installation considers locking.
The virtual machine interrupt handler pages aight also be considered
good candidates for locking. Other pages to pe locked depend upon the work being done by the
particular virtual aachine and its usage of virtual storage.
The normal CP paging aechanism selects unreferenced page fraaes in
real storage for replacement by active pages. Page fraaes belonging to
inactive virtual aachines will all eventually be selected and paged out
if the real storage fraaes are needed to support active virtual aachine
pages. When virtual aachine activity is initiated on an infrequent or
irregular basis, such as froa a remote terminal in a teleprocessing
inquiry system, soae or all of its virtual storage aay have been paged
out before the time the virtual machine must begin processing. Soae pages will then have to be paged in so that the virtual aachine can
respond to the teleprocessing request compared with running the saae teleprocessing prograa on a real machine. This paging activity aay cause
an increase in the tiae required to respond to the request coapared with
running the teleprocessing program on a real aachine. Further response tiae is variable, depending upon the number of paging operations that aust occur.
Locking specific pages of the virtual aachine's prograa into real
storage aay ease this problem, but it is not always easy nor possible to
identify which specific pages will always be required. Once a page is locked, it reaains locked until either the user logs
off or the system operator (privilege class A) issues the UNLOCK comaand for that page. If the "locked pages" option is in effect and the user
loads his system again (via IPL) or loads another systea, the locked
pages are refreshed and the virtual machine's locked pages are unlocked by the system. The SYSTEM CLEAR command, when invoked, clears virtual
aachine storage, including the user's locked pages.
1-28 IBM VM/310 System Logic and Problem Determination--Voluae 1

Note: In attached processor mode, no shared pages are locked. If the
system operator attempts to lock a shared page or an address range
containing one or more shared pages, he will receive the message DMKCPV165I PAGE (hexloc) NOT LOCKED, SHARED PAGE
for each of the shared pages within the range. RESERVED PAGE FRAMES OPTION A more flexible approach than locked pages is the reserved page frames option. This option provides a specified virtual machine with an
essentially private set of real page frames, the number of frames being designated by the system operator, when he issues the CP SET RESERVE command line: Pages will not be locked into these frames. They can be
paged out, but only for other active pages of the same virtual machine. When a temporarily inactive virtual machine having this option is
reactivated, these page frames are immediately available. If the
program code or data required to satisfy the request was in real storage
at the time the virtual machine became inactive, no paging activity is
required for the virtual machine to respond.
This option is usually more efficient than locked pages in that the
pages that remain in real storage are those pages with the greatest
aaount of activity at that moment, as determined automatically by the system. Although multiple virtual machines may use the LOCK option,
only one virtual machine at a time may have the reserved page frames option active. Assignment of this option is discussed further in
npreferred Virtual Machines.
n The reserved page frames option provides performance that is
generally consistent from run to run with regard to paging activity.
This can be especially valuable for production-oriented virtual machines
with critical schedules, or those running teleprocessing applications
where response times must be kept as short as possible. YIRTU1L=RE1L OPTION The VM/310 virtual=real option eliminates CP paging for the selected
virtual aachine. 111 pages of virtual machine storage, except page
zero, are locked in the real storage locations they would use on a real
coaputer. CP controls real page zero, but the remainder of the CP
nucleus is relocated and placed beyond the virtual=real machine in real
storage. This option is discussed in more detail in "Preferred Virtual Machines.
n Since the entire address space required by the virtual machine is
locked, these page frames are not available for use by other virtual
aachines except when the virtual=real aachine is not logged on. This
option often increases the paging activity for other virtual machine users, and in some cases for VK/310. (Paging activity on the system .ay
increase substantially, since all other virtual machine storage
requirements aust be aanaged with fewer remaining real page fraaes.)
CP Introduction 1-29