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Scalable paging space block allocator for a deferred storage computer operating system

IP.com Disclosure Number: IPCOM000020135D
Original Publication Date: 2003-Oct-28
Included in the Prior Art Database: 2003-Oct-28
Document File: 1 page(s) / 38K

Publishing Venue

IBM

Abstract

Extensible Method for Allocating Virtual Page State Information

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  Scalable paging space block allocator for a deferred storage computer operating system

Disclosed is an extensible method for dynamically allocating a data structure to record virtual page and disk state information in a Virtual Memory demand paging system. This data structure is called the External Page Table, or XPT. An individual entry in it is referred to as an XPT Entry, or XPTE. Each XPTE holds state information for one virtual page in the system. In order to support a lot of virtual memory, the XPT could get quite large. As a result, the XPT is pageable and also sparse. Sparse refers to the fact that XPTE's are only allocated when a virtual page is first used. In addition to page state information, if a virtual page has been written to a paging space disk, the location on disk, called a disk-block, is stored in its XPTE. The XPT, on a segmented system is partitioned into many segments. One way of creating these segments is, when a Virtual Memory segment is created, to ensure that there is enough XPT space pre-allocated to back all possible virtual pages in that segment. This will inherently over allocate XPT segments and waste resources. To conserve resources, it is desirable to create these segments only on demand, as a prior one fills up. A method for doing this is the subject of this paper.

The major difficulty in dynamically extending the XPT into another segment, is that at the points in time when it is desired to do this, the Virtual Memory Manager (V...