US 4,730,249 AGranted

Method to operate on large segments of data in a virtual memory data processing system

AssigneeInternational Business Machines Corporation

InventorsJohn T. O'Quin, II, John C. O'Quin, III

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Abstract

A method for use in a virtual memory data processing system employing a pageable External Page Table data structure for recording current status and disk address information for each virtual page in said system, provides improved system performance when a large number of virtual pages are to be operated on in the same manner. In accordance with the method, each page of External Page Table entries can record a predetermined number of entries (512), depending on the byte capacity of each virtual page (2,048) and the size of each entry (4 bytes). One page of 512 entries correspond to 1 megabyte of virtual storage (512.times.2,048) and also appears as one entry in a pinned External Page Table. The pinned External Page Table is referred to as the "XPT of the XPT," and has the same format as the pageable XPT. A 256 megabyte segment of virtual memory is representable in the XPT of the XPT by 256, 4 byte entries, or one-half of a page. Where all virtual pages represented by a page of XPT entries are to be processed in the same way (i.e., created, destroyed), one operation on one entry in the XPT of the XPT is made, rather than 512 operations on the 512 entries of the XPT.

A method used in a data processing system having a virtual memory for performing selected operations on entire large segments including a "create segment" operation, each said segment that is created having a unique address range and a plurality of virtual pages each having a virtual address within said unique address range, each said virtual page having a plurality of different states including a first state where said page is free and unreferenced and a second state where said page is committed, said committed virtual pages being demand paged into said system and stored at a physical location having a real address of a first storage device and paged into another storage location of a second storage device by a page faulting mechanism when required by said system, said system further including a plurality of pageable external page tables (XPTs), each XPT having at least one page of XPT entries, each said page of XPT entries having a virtual address and including k entries, each having n bytes, where k times n is equal to the byte capacity of a virtual page in said system, each said XPT entry having a first field for storing said real address of one of said virtual pages and a second field for storing an indication of said state of said one said virtual page, said "create segment" operation comprising the combination of the following steps,

(A) establishing one virtual segment having pages with virtual page addresses that correspond to real page addresses,
(B) storing said one virtual segment in said second storage device so that said one virtual segment in not pageable,
(C) providing a non-pageable data structure XPT.sup.2 having k' entries, each having n' bytes where k' times n' equals said byte capacity, each of said k' XPT.sup.2 entries having a first field for storing the virtual address of one said page of XPT entries and a second field for storing an indication that all of said pages represented by said XPT entries in said one page of XPT entries are either in said first state or said second state,
(D) establishing a sub-set of real addresses for said one virtual segment for storing a plurality of said XPT.sup.2 data structures, and
(E) changing said indication from said first state to said second state in at least one of said k' XPT.sup.2 entries corresponding to said address range of said newly created segment whereby a new segment is created having at least k virtual pages by changing only one said indication in one XPT.sup.2 entry for each said k pages created.

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Abstract

Claims10