Electrical computers and digital processing systems: memory – Storage accessing and control – Control technique
Reexamination Certificate
2000-01-04
2002-10-29
Kim, Hong (Department: 2187)
Electrical computers and digital processing systems: memory
Storage accessing and control
Control technique
C711S160000, C711S203000
Reexamination Certificate
active
06473842
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a virtual memory managing system for managing swap-out/swap-in relating to physical memory areas in a main storage device, segments in virtual memory space, and swap files in an auxiliary storage device in a virtual memory system.
2. Description of the Related Art
When swap-out became necessary in a virtual memory system, virtual memory managing systems of this type of the prior art carried out swap-out in page units. (Physical storage areas in a main memory device, segments in virtual memory space, and swap files in an auxiliary storage device are hereinbelow referred to as “memory areas.”)
When carrying out swap-out by page units in a virtual memory managing system of the prior art, a method is commonly adopted in which swap-out is performed by, for example, an algorithm that takes the page in use as LRU (Least Recently Used) to effectively carry out swap-out and swap-in of pages.
A virtual memory managing system of the prior art as described above, however, has the following problems.
First, because swap-out is carried out in page units by an algorithm such as LRU, swap-out of a page is carried out for the first time after page data (data within a page) have gone unused for a long time and have become old. The problem, therefore, is the existence of a certain amount of hold time until a page that actually is no longer used in tasks is swapped out. In other words, there was a problem of inefficient use of time in the memory management in a virtual memory system.
A second problem is that swap-out was carried in page units even when a task required that a memory area of large capacity be reserved, and swap-out of pages therefore had to be carried out repeatedly to reserve the necessary memory area. In other words, there was a problem of inefficient use of space in the memory management in the virtual memory system.
SUMMARY OF THE INVENTION
In view of the above-described problems, it is an object of the present invention to provide a virtual memory management system that enables memory management that is efficient in terms of both time and space in a virtual memory system through a “combination of swap-out in page units and swap-out in task units.”
Patent Gazette publications relating to the prior art of this invention include Japanese Patent Laid-open No. 25645/91, Japanese Patent Laid-open No. 174637/91, and Japanese Patent Laid-open No. 89221/94.
Japanese Patent Laid-open No. 25645/91 (Virtual Space Swapping System) relates to a technique in an information processing system that includes multiple virtual space and that manages this virtual space by segments and pages (pages being subdivided segments), the number of referenced pages (pages referenced in the relevant segment) being counted by segment, and swap-in being carried out while giving priority to segments having a large number of referenced pages so as to limit the total number of swapped-in pages. Although this technique shares with the present invention the object of providing efficient control of swap-out/swap-in, it differs entirely in terms of both viewpoint and constitution because it seeks to improve the swapping efficiency by reducing the number of swapped-in pages based on the count of referenced pages, in contrast to the present invention, which seeks to improve efficiency of swapping through “the combination of swap-out by page units and swap-out by task units.”
The technique of Japanese Patent Laid-open No. 174637/91 (Virtual Storage Control Method and Device) enables the reuse of used areas of a page when swapping out by preventing the erasing of these pages that are once recorded in an auxiliary storage device when swapping-in. This technique also shares with the present invention the object of efficient control of swap-out/swap-in. However, when swapping out, this technique determines whether or not areas of an auxiliary memory device can be reused and then determines whether areas are to be reused or newly reserved, and this technique therefore differs in terms of both viewpoint and constitution from the present invention, which seeks to improve efficiency of swapping out through “the combination of swap-out by page units and swap-out by task units.” In addition, when there is a request from a task to reserve memory areas, the present invention reserves areas within an auxiliary storage device (swap files) and at the same time reserves physical memory areas on a one-to-one basis, and the present invention therefore dues not require determination of whether or not areas of an auxiliary storage device are to be reused, as in the above-described art in the patent gazette.
Finally, Japanese Patent Laid-open No. 89221/94 (Computer System Memory Managing Method and Device) carries out judgments based on history information that has been made a vector (information recorded in a swap vector) when selecting pages that are to be paged out. Although this technique shares with the present invention the objective of efficient control of swap-out/swap-in, this technique seeks this improved efficiency through appropriate selection of pages that are to be paged out and therefore differs entirely in both viewpoint and constitution from the present invention, which seeks to improve efficiency of swapping through the “combination of swap-out in page units and swap-out in task units.”
Each of the above-described cases of the prior art has an entirely different constitution from the present invention as described hereinabove, and it goes without saying that even a combination of these cases of the prior art would not arrive at the technical idea of the present invention.
The virtual memory managing system of the present invention includes in a virtual memory system:
swap management tables provided with the items: page tag, update bit, and copy bit for each page;
memory area reserving means for, based on a memory area reserve request from a task, producing and managing the swap management table that corresponds to that memory area reserve request;
reserving, for that memory area reserve request, physical memory areas in a main storage device, segments in virtual memory space, and swap files in an auxiliary storage device;
and setting information in the swap management tables by means of the reservation of these memory areas;
swap-out control means for, when swap-out becomes necessary, determining whether swap-out should be carried out in page units or batch swap-out should be carried out in task units;
controlling and executing swap-out based on this determination;
and setting information indicating that pages that are subject to swap-out have been copied to swap files in the auxiliary storage device in copy bits for these pages in the swap management tables;
memory writing managing means for, when data within the pages have been updated, setting information indicating update of these pages in update bits for these pages in the swap management tables; and
swap-out object limiting means for effecting control such that, when batch swap-out is carried out in task units under the control of the swap-out control means, swap-out is not carried out for “pages that have been copied without being updated” based on update bits and copy bits in the swap management tables.
In more general terms, the virtual memory managing system of the present invention can be described as a construction in a virtual memory system having: a memory area reserving means for, based on a memory area reserve request from a task, reserving physical memory areas of a main storage device, segments in virtual memory space, and swap files in an auxiliary storage device; and swap-out control means for, when swap-out becomes necessary, determining whether swap-out should be carried out in page units or batch swap-out should be carried out in task units (for example, a determination to carry out swap-out in task units if the memory size of memory areas that are the requested object of the memory area reserve request that has brought about swap-out is greater than a reference va
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