Browse Prior Art Database

Blocked Page Input/Output in VSE/ESA

IP.com Disclosure Number: IPCOM000111580D
Original Publication Date: 1994-Mar-01
Included in the Prior Art Database: 2005-Mar-26
Document File: 4 page(s) / 154K

Publishing Venue

IBM

Related People

Beck, V: AUTHOR

Abstract

The concept of the 370/ESA architecture provides n virtual address and data spaces, each up to 2 GB. The virtual address space is separated in areas of 4K bytes, the so-called pages. The real storage is organized in areas of 4K bytes, the-so called frames. The pages not currently used by VSE/ESA are saved in an external storage medium which is called the Page Data Set (PDS). That means that all of the pages of the virtual address spaces are uniquely mapped on 4K-byte blocks of the PDS. The PDS is allocated in units of 8 blocks. This area is contiguous and may be read or written with a single Channel Command Word (CCW) program. Any reference to a page not yet in real storage causes a page fault.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 43% of the total text.

Blocked Page Input/Output in VSE/ESA

      The concept of the 370/ESA architecture provides n virtual
address and data spaces, each up to 2 GB.  The virtual address space
is separated in areas of 4K bytes, the so-called pages.  The real
storage is organized in areas of 4K bytes, the-so called frames.  The
pages not currently used by VSE/ESA are saved in an external storage
medium which is called the Page Data Set (PDS).  That means that all
of the pages of the virtual address spaces are uniquely mapped on
4K-byte blocks of the PDS.  The PDS is allocated in units of 8
blocks.  This area is contiguous and may be read or written with a
single Channel Command Word (CCW) program.  Any reference to a page
not yet in real storage causes a page fault.  VSE/ESA page management
selects a free frame to keep the referenced page in real storage and
reads the page from the PDS into the provided frame (page-in).  In
order to get a free frame, it might be necessary to save the
currently associated page on PDS (unconditional page-out) before
using the frame for the referenced page.  The intention of
pre-page-out is to make frames available for page replacement without
any unconditional page-out activity.

      Blocked paging is based on the allocation units of the PDS.
Whenever feasible, the page input/output (I/O) activities are carried
out in blocks of up to 8 pages in order to avoid single page I/O.
Blocked paging is carried out for pre-page-out, unconditional
page-out and page-in operations.

      The states of pages of an allocation unit are described by the
Page State List (PSL) of which there are two:  the Page-Out State
List (POSL) which is available for each address and data space and
indicates whether a page must be paged-out or not, and the Page-In
State List (PISL) which is available for one allocation unit only and
indicates whether page must be paged-in or not.  The POSL is provided
by the page selection algorithm.  The PISL is provided by the page-in
supervisor call (SVC) routine.

      The state descriptor of the PSL is implemented as a bit string,
indicating whether the condition is satisfied or not.  Its value can
be used as index into tables provided to control blocked page I/O.
The states of the total allocation unit are called the PISL value and
the POSL value, respectively.  The corresponding state of one page is
called the PISL / POSL mask.

      Blocked page I/O is triggered by the value of the actual
allocation unit in the PISL and the POSL, respectively.  Blocked
pre-page-out is started if the minimal blocking factor is reached.
Whenever possible, an unconditional page-out operation is combined
with a pre-page-out operation in order to do blocked page I/O
operation.  This is achieved by inspecting the POSL of the related
allocation unit.  Depending on the value of the PISL, blocked page-in
is performed.  The value of the PISL is supplied by the PAGE-IN SVC
routine.

      A blocked pre-...