Browse Prior Art Database

Set Management Technique

IP.com Disclosure Number: IPCOM000084600D
Original Publication Date: 1975-Dec-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 5 page(s) / 53K

Publishing Venue

IBM

Related People

Duke, AH: AUTHOR

Abstract

A data storage set management technique is described which provides improved storage efficiency and a reduced number of storage references for a chain type set of storage items, wherein the relative position or order of the items in the chain is immaterial and wherein the items enter the set and leave the set in no particular order. This technique is particularly useful in connection with the operation of a virtual storage data processing system.

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Set Management Technique

A data storage set management technique is described which provides improved storage efficiency and a reduced number of storage references for a chain type set of storage items, wherein the relative position or order of the items in the chain is immaterial and wherein the items enter the set and leave the set in no particular order. This technique is particularly useful in connection with the operation of a virtual storage data processing system.

The technique described herein is an extension of the "Storage Allocation Mechanism" described at pages 2606-2610 of the February 1975 issue (Volume 17, No. 9) of the IBM Technical Disclosure Bulletin. This earlier technical article describes the use of a bit mask or control mask associated with each storage page, for use in maintaining a list for a single set of storage items. The enhanced technique described in this article goes a step farther and enables one and the same bit mask or control mask on each page to be used to maintain separate lists for two separate but related sets of storage space items.

In the earlier described mechanism, the set was a chain structure called the "free list" and included all the storage elements in a given storage space that were free or not in use. In the technique described herein, one set is a chain structure called the "free set" and the other set is a chain structure called the "used set". The free set is the same as the free list of the earlier published article and, as such, includes all the storage elements that are free or not in use. The used set, on the other hand, includes all the storage elements in a storage space that are in use for data storage purposes or the like.

The relationship between sets is that both sets share the same common storage space and each storage element in the space must be in one set or the other, but not both. Thus, one set is the complement of the other in terms of element membership. This relationship enables one and the same control mask to be used for both sets or lists. As will be seen, the control mask for the free set is the complement of the control mask for the used set. Consequently, only one of these control masks need be physically maintained.

Fig. 1 illustrates three typical storage pages in the storage space being considered. The storage space in question is divided into many pages of the same fixed size and each page is subdivided into a fixed number of equal size element spaces. Each element space is capable of holding the same fixed number of data bytes, a byte being the smallest unit of addressable storage in the system. One page is called the header page and contains the customary header type information, together with certain page pointers used in connection with the list structures. The remainder of the pages (only two of which are shown in Fig. 1) are called data pages and are used for storing data.

The lastmost element space or spaces on each data page are used for stor...