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Job Oriented Page Replacement

IP.com Disclosure Number: IPCOM000081762D
Original Publication Date: 1974-Aug-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 3 page(s) / 42K

Publishing Venue

IBM

Related People

Bowen, AJ: AUTHOR

Abstract

This is an improvement to a job-oriented page replacement algorithm for preventing a shift in system equilibrium resulting from real memory contention. The improvement includes a longevity parameter mechanism, which permits the system equilibrium to be made independent of real memory contention.

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Job Oriented Page Replacement

This is an improvement to a job-oriented page replacement algorithm for preventing a shift in system equilibrium resulting from real memory contention. The improvement includes a longevity parameter mechanism, which permits the system equilibrium to be made independent of real memory contention.

In a computer system with virtual storage, the working set concept has been useful in deciding what sort of workload can be effectively processed. The working set may be defined as that number of real memory page frames which, when allocated to a job, will keep nonproductive paging at or below a tolerable level for that job.

As the computer operates, all real memory page frames will eventually become full. When a page fault subsequently occurs, it becomes necessary to reallocate a real memory page frame for the new page. Some systems accomplish this by determining the Least Recently Used page on a global basis, in which all page frames are considered without regard to which active job owns them.

Under conditions of no real memory contention, the system will reach some equilibrium between its ability to load I/O subsystems and its ability to load the CPU. As real memory contention increases, system equilibrium shifts away from loading the CPU.

The equilibrium-shift problem can be solved by defining a number of job- categories, e.g., teleprocessing (TP) or batch. For each category, a longevity parameter is explicitly stated in realtime, i.e., the minimum amount of time that a page must stay in real memory after loading, regardless of reference.

When searching for a page frame to reallocate, the page replacement algorithm must still find an unreferenced frame. However, it must determine whether the time since loading is greater than the minimum specified for the job category. If the time is not greater than the minimum time specified, then the frame may not be reallocated. The longevity parameter mechanism provides the capability to guarantee working set to I/O bound tasks. This provides an ability to effectively drive an I/O subsystem despite vigorous real memory contention between jobs.

Fig. 1 illustrates a hypothetical situation, in which a longevity parameter is utilized to prevent a shift in system equilibrium resulting from real memory contention. Assume that there are 100 frames of pagable real memory and that the paging device is capable of servicing...