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Increased Swap Group Size with Extended Swap

IP.com Disclosure Number: IPCOM000045123D
Original Publication Date: 1983-Feb-01
Included in the Prior Art Database: 2005-Feb-06
Document File: 2 page(s) / 14K

Publishing Venue

IBM

Related People

Beretvas, T: AUTHOR [+2]

Abstract

This article describes an increased swap group size improvement in the extended swap control program described in another article. Extended swap writes out the entire swap-in set, i.e., all the referenced pages (changed or unchanged), and LSQA (local system queue area) pages to swap datasets, so that at swap-in time the entire swap-in set can be read from the swap datasets as an entity (or more precisely, several swapset entities) in a single stage operation.

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Increased Swap Group Size with Extended Swap

This article describes an increased swap group size improvement in the extended swap control program described in another article. Extended swap writes out the entire swap-in set, i.e., all the referenced pages (changed or unchanged), and LSQA (local system queue area) pages to swap datasets, so that at swap-in time the entire swap-in set can be read from the swap datasets as an entity (or more precisely, several swapset entities) in a single stage operation.

Changed unreferenced pages are trimmed from the working set at swap-out time, and they are written onto the local page datasets. The swap-out process is therefore still a two-stage process: the trimmed changed pages are written to local page datasets, and upon completion of these operations the swap-in set is written to swap datasets. The swap-in process is a one-stage process, the swap-in set is retrieved from the swap datasets.

Both extended swap-out and swap-in processes are illustrated in (T. Beretvas, R.S. Clark and S. Friesenborg, "Extended Swap Control for Paged Data," IBM Technical Disclosure Bulletin 25, 4529-4532 (February 1983, this issue).

System performance can be improved in a system with extended swap by providing increased swap group size. It is well known that page faulting by a user can be decreased if the pages in the working set are increased as long as the pages in the working set are relevant to the user.

This concept forms the basis for increasing the swap group size. The IBM MVS/370 system control program presently has a feature called protected minimum working set size (PWSS), the intention of which is to guarantee a minimum number of real storage frames for an address space. The specified number of frames are guaranteed for the address space in main storage as long as the user has sufficient frames to fill up the protected size. This feature also guarantees that if the user...