the full simulation. Once the IPL sequence has completed, CCW translation can be bypassed by issuing the SET NOTRANS ON command. When the virtual machine demands a page frame through normal use of CP's page tables, the paging routine recognizes the virtual=real
capability. It then assigns the virtual page to the equivalent real pageframe and does not perform a paging operation, because all these pages
are resident a nd are ne ve r swa pped out.
Note: The virtual machine running with virtual=real is still run inSystem/310 relocate mode.
Virtual210x lines and sense operations from the virtual machine do
not use the virtual=real function. These invokeCCW translation for the
virtual enable/disable lines and the transfer of the sense bytes.The UNLOCK command has a VIRT=REiL operand that essentially releases
the virtual=real area fornormal system paging use. Once the area has
been released, it can only be reclaimed for additional virtual=real
operations only by anIPL of the VM/310 system. The size of the
virtual=real area is an installation specification that is part of the
special nucleus generation procedure that is outlined in theV!/3IQ Rlanni.D.9 and Syste,! Generati2!! Guide. The size of the area must be
large enough to contain the entire addressing space of whatever virtual
aachine wishes to occupy thatspacee A virtual machine can use a smaller
space than is provided but cannot use a larger space without
regenerating theCP nucleus. DASD STORAGE !ANAGE!ENT Any virtual machine's virtual storage pages that have been referenced
but are not resident in real storage must be kept in slots on theDASD paging device. DASD page space is assigned only when the page is
selected for a page-out. CertainDASD pages may also be marked read-only. Thus, the DASD address slot initially associated with the
page should be considered to be the source of the page only. If the
page is changed after it has been read into real storage, a new slotmust be obtained when .it is paged out. Examples of read-only pages are those which contain portions of pageable saved systems and pages which
are part of asystem spool file. Slots can be reassigned when DMKPTRAN finds that it must swap a page out to a movable-head DASD device. In
this case, the old slot is released and the new slot is obtained.
If a new slot is required,DMKPGT is called to supply the address of an
available slot.DMKPGT maintains a chain of cylinder allocation aaps for
each cylinder that has been assigned for either virtual storage or spool
file paging. The allocation chains for spooling are kept separately
from those used for paging so that they can be check pointed in case of a
system failure. However, in other respects they are thesaae. The
allocation blocks for a givenvolume are chained from the RDEVBLOK for
the device on which thevolume is aounted. The chains of cylinder and
slot allocation blocks are initialized byD!KCPI. Each block on an
allocation chain represents oneCYlinder of space assigned to paging,
and contains a bitaap indicating which slots have been allocated and
which are available. Each block also has a pointer to the next
allocation block on the chain, a cylindernumber, and a record count. D!KPGT searches this list sequentially until an available slot is found; CP Introduction 1-111
capability. It then assigns the virtual page to the equivalent real page
are resident a nd are ne ve r swa pped out.
Note: The virtual machine running with virtual=real is still run in
Virtual
not use the virtual=real function. These invoke
virtual enable/disable lines and the transfer of the sense bytes.
the virtual=real area for
been released, it can only be reclaimed for additional virtual=real
operations only by an
virtual=real area is an installation specification that is part of the
special nucleus generation procedure that is outlined in the
large enough to contain the entire addressing space of whatever virtual
aachine wishes to occupy that
space than is provided but cannot use a larger space without
regenerating the
but are not resident in real storage must be kept in slots on the
selected for a page-out. Certain
page should be considered to be the source of the page only. If the
page is changed after it has been read into real storage, a new slot
are part of a
this case, the old slot is released and the new slot is obtained.
If a new slot is required,
available slot.
each cylinder that has been assigned for either virtual storage or spool
file paging. The allocation chains for spooling are kept separately
from those used for paging so that they can be check pointed in case of a
system failure. However, in other respects they are the
allocation blocks for a given
the device on which the
slot allocation blocks are initialized by
allocation chain represents one
and contains a bit
which are available. Each block also has a pointer to the next
allocation block on the chain, a cylinder