Method for reducing disk I/O accesses in a multi-processor clustered type data processing system

• US 5,239,643 A
• Filed: 07/19/1991
• Issued: 08/24/1993
• Est. Priority Date: 11/30/1987
• Status: Expired due to Term

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Morgan, Stephen P., Blount, Marion L., Rader, Katalin A. V.
• Primary Examiner(s): Kulik, Paul V.
• Application Number:
  US07/732,949
• Time in Patent Office: 767 Days
• Field of Search: 364/DIG. 1, 364/DIG. 2, 364/132, 364/133, 364/134, 395/425, 395/600, 395/650, 395/200, 395/800, 395/275, 371/10, 371/13
• US Class Current: 1/1
• CPC Class Codes: G06F 12/08 in hierarchically structured memory systems, e.g. virtual memory systems
• CPC Class Codes: Y10S 707/99943 Generating database or data structure, e.g. via user interface

Abstract

A method for minimizing I/O mechanical assess operations on secondary storage devices in a data processing system having a plurality of processor units interconnected in a cluster configuration to permit each processor unit to request and obtain data that is resident only on a secondary storage device of one processor unit. The method involves the steps of maintaining at each processor unit information about each copy of data that has been sent from the unit to another unit to permit a second request to the unit to be serviced by transferring a copy of the data from the main memory which is storing the data to the requesting unit rather than servicing the request with a relatively slow I/O accessing operation to a secondary storage device.

Claims

1. A method to minimize I/O access operations in a data processing system having

A) a plurality of processor units comprising a first processor unit with a first main memory, first operating systems, and first secondary storage device;

a second processor unit with a second main memory and second operating system; and

a third processor unit with a third main memory and third operating system; and

B) a switch for selectively interconnecting any pair of said units in a data transferring relationship to permit data that is stored in said first memory to be transferred to said third main memory in response to request from said third unit to said first unit, said method comprising the following steps in combination;

A) maintaining by each said first, second and third operating system,

(a) a list of each of the files stored in said data processing system, and

(b) an indication of which of said processor units is the access coordinator for said each of said files,

B) opening one of said files, stored at said first processor unit as identified by said indication in response to a request to said first processor unit for specified information from said second said processor unit,

C) transferring from said first secondary storage device of said first processor unit to said first main memory and thereafter transferring from said first main memory to said second main memory said specified information from said one of said files in response to said request by said second processor unit, and discarding said specified information from said first main memory, and

D) thereafter transferring said specified information from said second main memory to said third main memory in response to a request from said first operating system to said second operating system, that was prompted by a request to said first operating system from said third operating system for said specified information.

2. The method set forth in claim 1 in which said step of maintaining by each said first, second and third operating system further comprises the step of

(a) maintaining by said each first, second, and third operating system a corresponding Virtual Shared Memory (VSM) Table one said VSM Table identifying which of said processor units has a copy of said specified information that is being coordinated by said access coordinator.

3. The method set forth in claim 2 in which said step of transferring from said first main memory to said second main memory further comprises the step of

(a) updating said VSM Table of said first operating system to reflect that said specified information is stored in said second main memory.

4. The method set forth in claim 3 in which said step of transferring said specified information from said second main memory to said third main memory included the further step of

(a) updating sad VSM Table of said first processor unit to indicate that a copy of said specified information is stored in said third main memory.

5. A method in a data processing system having

a first processor unit with a first main memory, first operating system, and first secondary storage device;

a second processor unit with a second main memory and second operating system; and

a third processor unit with a third main memory and third operating system, said first, second, and third processing units being interconnected by a communication link, said method comprising the following steps;

A) maintaining by each said first, second, and third operating system indications of which of said processor units coordinates access for a file in the data processing system;

B) maintaining by said first operating system information which indicates that a copy of said file is currently maintained in said second main memory and is not currently maintained in said first main memory, and

C) servicing a request by said third processor unit to said first processor unit for a copy of said file, said request being directed to said first processor unit by one of said indications indicating at said third processor unit that said first processor unit coordinates access to the identified data, said servicing causing said second processor unit to transfer a copy of said file to said third main memory, rather than said first unit servicing said request by an I/O operation to said first secondary storage device if said file is not in said first main memory.

6. The method recited in claim 5 in which said system further includes a second and third secondary storage device for said second and third processor unit respectively, and wherein

(a) said first, second, and third main memory and said respective first, second, and third secondary storage device of each said respective first, second, and third processor unit comprise a virtual memory for said respective first, second, and third processor unit, each said virtual memory having the same virtual address range, that includes a plurality of contiguous segments, each of which includes a plurality of virtual page addresses,

(b) said first, second, and third secondary storage device comprises, respectively, a plurality of block addressable storage locations each of which stores a page of data,

(c) said first, second, and third main memory comprises, respectively, a plurality of page frames for storing a page of data,

(d) each of said first, second, and third processor units having the same operating system including a memory manager having a page fault handling mechanism for resolving page faults that occur in response to requests from an application program to process a page of data that is not in main memory, and

(e) a switch is activated by said first, second and third processing units for selectively interconnecting any two of said first, second, and third processor units, said method including the further steps of

storing in each said respective virtual memory a copy of said same operating system and further storing at least one application program in a corresponding said virtual memory of at least one of said first, second, and third processor units, and

coordinating access requests to said at least one application program from other of said first, second, and third processor units by one of said first, second, an third processor units controlling one of said segments of said corresponding said virtual memory where said at least one application program is stored.

7. The method recite in claim 6 in which said step of maintaining information by said first operating system includes the further steps of

(a) establishing a first data structure having a plurality of entries for storing a unique identifier for each said at least one application program stored in said system, and a processor unit ID to designate an Accessor Coordinator (AC) for each said stored at least one application program, and

(b) storing said first data structure in said first, second, and third main memory.

8. The method recited in claim 7 in which said step of maintaining information by said first operating system includes the further steps of

(a) establishing a second data structure having a plurality of entries, each of which stores an indication of the virtual address of a page of data transferred from a file being coordinated by said first processor unit, and the identity of a remaining said second or third processor unit that has a copy of said transferred page.

(b) storing said second data structure in said first, second and third main memory, and

(c) updating said first and second data structures as pages of data are transferred between said first, second, and third processing unit during said step of servicing.

9. The method recited in claim 8 including the further step of

(a) resolving local page faults in one of said first, second, and third processor units with said memory manager by first determining from said second data structure whether a copy of the page which caused the local fault is stored in a corresponding first, second or third main memory of another of said first, second or third processor units before resoling said fault with said page fault handling mechanism of said first, second, or third one of said processor units.