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Browse Prior Art Database

Release Page Service

IP.com Disclosure Number: IPCOM000081982D
Original Publication Date: 1974-Sep-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 4 page(s) / 58K

Publishing Venue

IBM

Related People

Lubart, BP: AUTHOR

Abstract

Release page is a supervisor service, which functions to make available all real and auxiliary storage wholly associated with an area of virtual address space. The virtual address space remains allocated, i.e., the area remains addressable, but the contents of the address space are released.

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Release Page Service

Release page is a supervisor service, which functions to make available all real and auxiliary storage wholly associated with an area of virtual address space. The virtual address space remains allocated, i.e., the area remains addressable, but the contents of the address space are released.

In a virtual storage system when a program refers to a virtual address, the address is translated by dynamic address translation into its corresponding real storage address. To facilitate address translation, virtual storage is logically divided into segment blocks each of which, in turn, is divided into page blocks.

The address translation arrangement uses a two-level table look-up process to determine the real storage address. The first level table, the segment table, contains an entry for each segment of virtual storage. Each segment table entry points to a second level table, the page table, which contains an entry for each page in the corresponding segment. The page table entry contains the base address of the page in real storage.

A specific virtual page, as represented by a page table entry, has at least two attributes. The first deals with the fact that the address space represented by that page table entry has been allocated or not by GETMAIN. This attribute is indicated by the presence (1) or absence (0) of a page assigned flag (PAF) associated with the page table entry. The second refers to the fact that a page represented by the page table entry resides or not in real storage. This attribute is indicated by the absence (0) or presence (1) of a page validity flag (PVF) associated with the page table entry.

Because a program's virtual address space may be larger than real storage, it must exist partly in real storage and partly in auxiliary storage. The part of auxiliary storage used to store pages is called the external page storage. An external page table is maintained to keep track of all pages on the external page storage. For every page table entry, there is a corresponding external page table entry which contains the external page storage address, at which that page is recorded on a paging device.

A specific virtual page, as represented by an external page table entry, has an attribute similar to that represented by a page table entry, namely, that the page represented by the external page table entry resides or not on external storage. This attribute is indicated by the presence (1) or absence (0) of an external storage validity flag (ESVF) associated with the external page table entry.

Real storage is subdivided into blocks of storage termed page frames, with each real storage page frame being the same size as a page. Thus, when pages are loaded into real storage from a program's address space, they are placed into page frames of real storage. The status of each page frame, whether it is in use, i.e., contains an active page or whether it is available for use, is indicated by an entry in a page frame tabl...