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Pageable Nucleus Page Fault Minimization Algorithm

IP.com Disclosure Number: IPCOM000079006D
Original Publication Date: 1973-Apr-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 3 page(s) / 86K

Publishing Venue

IBM

Related People

Brannon, TL: AUTHOR [+2]

Abstract

Page faults contribute to performance degradation in a virtual storage system. This algorithm is used to arrange pageable nucleus control sections so as to minimize the paging required for their execution. The process is called pageable control section (CSECT) packaging.

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Pageable Nucleus Page Fault Minimization Algorithm

Page faults contribute to performance degradation in a virtual storage system. This algorithm is used to arrange pageable nucleus control sections so as to minimize the paging required for their execution. The process is called pageable control section (CSECT) packaging.

The packaging algorithm is sensitive to the logical association of particular CSECT groups. For instance, if CSECT A is likely to be executed when CSECT B is executed, then A and B should be packaged together on one virtual page. Only one page fault occurs if the CSECTs must be paged into real storage. If their combined size is such that one of the CSECTs must overlap a page boundary in order to be packaged with the other CSECTs, the pages on which the CSECTs are packaged are contiguous. The result is fewer page faults than if the CSECTs are scattered at random in the pageable nucleus. Logical association in the primary consideration of the packaging algorithm, and address assignment on this basis is called forced packaging. Fig. 1 shows that CSECTs A, B, C, and D are forced packaged onto two virtual pages. CSECTs E and F are also logically associated and therefore packaged together on a page.

A second consideration is CSECT size. No CSECT smaller than the system page size (2K bytes assumed in Fig. 1) should overlap a page boundary, since a page fault can occur for each page that the CSECT occupies. The packaging algorithm dynamically assigns addresses to these CSECTs on a best fit basis. Some virtual pages may not be completely, filled because of the gaps resulting when page boundary overlaps are prevented; but that loss of virtual space i...