Browse Prior Art Database

Swapping of Partitions in VSE/ESA

IP.com Disclosure Number: IPCOM000115604D
Original Publication Date: 1995-May-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 4 page(s) / 127K

Publishing Venue

IBM

Related People

Beck, V: AUTHOR

Abstract

Disclosed is a determination method for the "working set" and its corresponding usage for the "swap-in"/"swap-out" processing implemented and used within the VSE/ESA operating system. The method is based on the change and reference information made available per page by the underlying hardware (/390(*) architecture in this case)

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This is the abbreviated version, containing approximately 49% of the total text.

Swapping of Partitions in VSE/ESA

      Disclosed is a determination method for the "working set" and
its corresponding usage for the "swap-in"/"swap-out" processing
implemented and used within the VSE/ESA operating system.  The method
is based on the change and reference information made available per
page by the underlying hardware (/390(*)  architecture in this case)

      In VSE/ESA the pages of the virtual address areas are saved
onto an external storage medium which is called the Page Data Set
(PDS).  The PDS is allocated in units of 8 blocks on one or more data
extents residing on one or more disk devices.  The page input/output
(I/O) requests are queued in the related device queues.  The pages
currently used by VSE/ESA are associated to frames of the real
storage; these pages are called the working set of the system.
Accordingly, the working set of a partition consists of the pages
which belongs to the partition and are currently addressable in the
real storage.

The essential mechanisms for the VSE/ESA page management are:
  1.  Reference and Change Bits:
      An addressable page is characterized by the reference and
change
       bits.  The change bit is set to ON by the hardware whenever a
       page has been changed and it is reset to OFF by VSE/ESA when
the
       page is saved on the PDS.  Whenever a page has been referenced
       the hardware sets the reference bit to ON; VSE/ESA does the
same
       after the page has been made addressable.  The reference bit
is
       reset to OFF by VSE/ESA page selection and page management
       services.
  2.  Maintenance of Page State Lists (PSLs):
      The Page State List (PSL) describes the states of contiguous
       pages of the corresponding virtual address areas.  The state
       descriptor of the PSL is implemented as a bit string,
indicating
       whether the condition of interest is satisfied or not.
  3.  Page Selection and Page Replacement:
      If a page fault occurs, VSE/ESA page management selects a frame
       from the Invalid Page Frame Queue (IPFQ), or in case of an
empty
       IPFQ, from the Page Frame Selection Queue (PSQ).  The IPFQ
       consists of all currently unused frames.  The PSQ consists of
the
       frames associated to pages which are currently available for
the
       page selection.
      The page replacement strategy is an approximation of the Last
       Recently Used (LRU) algorithms.

      When in VSE/ESA the currently active partition is made unready
the working set of this partition remains untouched by the
dispatching algorithms and is reduced afterwards page by page until
it is consumed completely.  On the other hand, the working set of the
recently active partition must be reestablished page by page whenever
the partition is made ready again.  It is much more efficient to
release the work...