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Swap Faulting and Partial Swap

IP.com Disclosure Number: IPCOM000043236D
Original Publication Date: 1984-Aug-01
Included in the Prior Art Database: 2005-Feb-04
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Beretvas, T: AUTHOR [+6]

Abstract

A new concept of "swap-faulting" and "partial swap" is described as part of a virtual machine control program (CP). CP swapping involves a new page-selection mechanism. The new concept results in replacing the large majority of demand paging operations by blocked (swap) paging, i.e., moving multiple pages per start I/O instruction. The new selection relies on the page reference bits being set by a virtual machine in its execution. When the virtual machine finishes its (dispatch) Q-stay, i.e., is Q-dropped, then the working set for this virtual machine is identified. Pages not belonging in the working set are "trimmed"; they are moved onto the flush list, being made available. The working set of the Q-dropped user is broken up into groups of pages, called swapsets.

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Swap Faulting and Partial Swap

A new concept of "swap-faulting" and "partial swap" is described as part of a virtual machine control program (CP). CP swapping involves a new page- selection mechanism. The new concept results in replacing the large majority of demand paging operations by blocked (swap) paging, i.e., moving multiple pages per start I/O instruction. The new selection relies on the page reference bits being set by a virtual machine in its execution. When the virtual machine finishes its (dispatch) Q-stay, i.e., is Q-dropped, then the working set for this virtual machine is identified. Pages not belonging in the working set are "trimmed"; they are moved onto the flush list, being made available. The working set of the Q- dropped user is broken up into groups of pages, called swapsets. These pages are chained together, and they are (conceptually) moved onto a new list called "swap list", which points at swappable swapsets. Whenever the free list falls below its threshold value, one (or more) swapsets are removed from the swap list, the pages in the swapset are written out to a swap (paging) DASD (direct- access storage device), subsequent to which the frames can be freed up. The result is that a group of pages (a swapset) is written into consecutive locations on the DASD, instead of a single page. The pages are retrieved from the swap DASD also in swapset form (i.e., multiple pages). This retrieval is prompted by swap-faulting, which means that a page-...