Dismiss
InnovationQ will be updated on Sunday, Oct. 22, from 10am ET - noon. You may experience brief service interruptions during that time.
Browse Prior Art Database

Disable Reference Storage

IP.com Disclosure Number: IPCOM000107527D
Original Publication Date: 1992-Mar-01
Included in the Prior Art Database: 2005-Mar-21
Document File: 2 page(s) / 89K

Publishing Venue

IBM

Related People

Eilert, CK: AUTHOR [+3]

Abstract

In MVS programs that must run disabled, fixed virtual storage is used in order to avoid taking page faults. Global fixed virtual storage must always be valid in central storage. Local fixed virtual storage must be valid in central storage when the associated address space is swapped in. These attributes of fixed virtual storage are overkill for the needs of disabled programs and can adversely affect system performance by making the central storage backing the fixed virtual unavailable for other uses.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Disable Reference Storage

       In MVS programs that must run disabled, fixed virtual
storage is used in order to avoid taking page faults. Global fixed
virtual storage must always be valid in central storage.  Local fixed
virtual storage must be valid in central storage when the associated
address space is swapped in.  These attributes of fixed virtual
storage are overkill for the needs of disabled programs and can
adversely affect system performance by making the central storage
backing the fixed virtual unavailable for other uses.

      Disabled Reference (DREF) storage solves the problem with a new
type of virtual storage.  DREF storage in MVS has some of the
attributes of fixed storage (i.e., it can be referenced by disabled
programs), without the major drawback of fixed storage (permanent
occupancy in central storage). DREF virtual storage can reside in
central storage or on expanded storage which frees up central storage
for other uses.

      The expanded storage feature in the IBM System/390* (S/390)
systems provided the base for the new MVS paging capabilities.  The
operations from/to expanded storage are synchronous in nature.  There
is no starting a channel program and then waiting for an interruption
to signal its end.  Also, the operations from/to expanded storage are
fast enough to be performed synchronously for most disabled routines.

      DREF storage is allowed to move to expanded storage, but not to
auxiliary storage (DASD).  This allows a disabled routine to take a
page fault and have it resolved immediately, without suspending the
running program.  DREF storage is also not brought in to central
storage until it is first referenced by a program.

      This article describes how DREF storage can be implemented.
VIRTUAL STORAGE OBTAIN

      When the virtual storage is obtained (via GETMAIN, for
example), the page tables are marked to indicate that the virtual
storage has the DREF attribute (can be referenced disabled).  When
the virtual storage i...