Browse Prior Art Database

Segment Space Support

IP.com Disclosure Number: IPCOM000100110D
Original Publication Date: 1990-Mar-01
Included in the Prior Art Database: 2005-Mar-15
Document File: 3 page(s) / 92K

Publishing Venue

IBM

Related People

Good, CE: AUTHOR [+5]

Abstract

A saved segment shares pages on an architected segment boundary. A saved segment is defined such that its definition indicates that it contains the whole segment for its domain. Its data does not necessarily have to occupy the whole segment area, but its name implies that it owns the whole segment. This form of implementation has a one to one relationship with the definition of an architected segment by the respective architecture. In IBM System/370 Extended Architecture, a segment size is defined as one megabyte (Mb) or 256 pages. In IBM System/370 Architecture, a segment size is defined as 64 Kilobytes (Kb) or 16 pages.

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Segment Space Support

       A saved segment shares pages on an architected segment
boundary.  A saved segment is defined such that its definition
indicates that it contains the whole segment for its domain.  Its
data does not necessarily have to occupy the whole segment area, but
its name implies that it owns the whole segment.  This form of
implementation has a one to one relationship with the definition of
an architected segment by the respective architecture.  In IBM
System/370 Extended Architecture, a segment size is defined as one
megabyte (Mb) or 256 pages.  In IBM System/370 Architecture, a
segment size is defined as 64 Kilobytes (Kb) or 16 pages.

      In the prior-art applications that were restricted to a segment
boundary, only a single product or application could exist in the
same architected segment, even if the page ranges of the individual
products did not overlap.  Since only a single product code/data
could occupy an architected segment, use of only a small portion of
the pages within the segment results in a large amount of wasted
space.  It should be noted that the same is true with System/370
Architecture 64Kb segments; however, the effect of wasted space is
not as great as with the System/370 Extended Architecture (Fig. 1).

      The benefit of using saved segments is to save on system
resources (Fig. 2).  Segments can be shared, meaning that more than
one virtual machine user can share the same real storage pages with
another virtual machine user.  The following real system resources
are saved:
1.   Direct-Access Storage Device (DASD) paging slots (DASD slot -
4Kb records).
2.   System paging space (real storage).
3.   Number of control blocks allocated for page and ASA tables.
(ASA means Auxiliary Storage Address + Maintains Storage Pages on
DASD). Sharing on a page table means:
1.   Saving on the number of control blocks needed for page tabl...