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Accelerated Frame Replacement for Swap In Requests

IP.com Disclosure Number: IPCOM000051162D
Original Publication Date: 1982-Aug-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Pierce, BR: AUTHOR [+3]

Abstract

In a virtual storage operating system such as MVS/System Product Release 3, where group page operations are used to swap users into and out of real storage frames to satisfy swap-in requests. This requirement can be quite variable depending on the system's swap rate and the number of pages in the user's working set. (A user's working set consists of those pages referenced during a variable length interval prior to swap out and all pages that were fixed in real storage at the time the user was swapped out.) The supply of available frames must be enough to also satisfy a normal load of single page-in requests (demand page-ins) from response-sensitive application programs.

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Accelerated Frame Replacement for Swap In Requests

In a virtual storage operating system such as MVS/System Product Release 3, where group page operations are used to swap users into and out of real storage frames to satisfy swap-in requests. This requirement can be quite variable depending on the system's swap rate and the number of pages in the user's working set. (A user's working set consists of those pages referenced during a variable length interval prior to swap out and all pages that were fixed in real storage at the time the user was swapped out.) The supply of available frames must be enough to also satisfy a normal load of single page-in requests (demand page-ins) from response-sensitive application programs.

This article describes how such a system can perform page frame replacement in a way that responds to varying swap-in loads by varying the frame-stealing threshold with the swapping load. Frame replacement, also known as frame stealing, picks currently allocated frames to be made available to other users, writes any changed pages to auxiliary storage, and marks the frames available. The method of frame replacement described here has a two- fold purpose: (1) ensure the successful swap-in of a user, even one with a very large working set, and allow multiple simultaneous swap-ins; and (2) ensure demand page-ins are not delayed waiting for real storage behind swap-in requests.

The above goals are achieved by increasing the rate of frame stealing when necessary to satisfy outstanding swap-in requests. Before a...