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CP/370 to Page Cache Performance Extension

IP.com Disclosure Number: IPCOM000034193D
Original Publication Date: 1989-Jan-01
Included in the Prior Art Database: 2005-Jan-27
Document File: 1 page(s) / 13K

Publishing Venue

IBM

Related People

Bloom, MA: AUTHOR [+3]

Abstract

The IBM Control Program/370 (CP/370) extension provides a link between the page cache and the IBM System/370 (S/370) operating system. With this link, CP can pass information to the cache that was previously unavailable. The information can increase the cache hit ratio, which will increase performance. In Virtual Machine/Personal Computer (VM/PC), the local S/370 operating system is not aware if Page Cache is present. The page file response times will often be faster, but there is no change in the way CP requests page file activity. This isolation from CP means that the benefits of cache may be obtained without changing CP. But it also implies that the cache must work without any information from CP.

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CP/370 to Page Cache Performance Extension

The IBM Control Program/370 (CP/370) extension provides a link between the page cache and the IBM System/370 (S/370) operating system. With this link, CP can pass information to the cache that was previously unavailable. The information can increase the cache hit ratio, which will increase performance. In Virtual Machine/Personal Computer (VM/PC), the local S/370 operating system is not aware if Page Cache is present. The page file response times will often be faster, but there is no change in the way CP requests page file activity. This isolation from CP means that the benefits of cache may be obtained without changing CP. But it also implies that the cache must work without any information from CP. If a page is written to the page file, the cache software retains that page in random-access memory (RAM), or disk, until another page with the same virtual address overwrites it. By writing over the page, CP signifies that it is no longer needed. But this release of pages occurs one page at a time. The cache performance will suffer from maintaining pages that CP and Conversational Monitoring System (CMS) no longer need. An unneeded page may even be backed out to the hard disk if it becomes the least recently used page before CP re-uses its virtual page number. Because page cache does not know which pages are valid to CP, and which are not, it must manage all pages as if they are valid. The CP extension provides the page cache software with the information needed to get rid of pages that CP has invalidated. The cache software can then improve its management of the limited RAM and increase local S/370 performance. CP often releases large blocks of pages, so the performance gain will be significant. The only return code for a "page file creat...