Electrical computers and digital processing systems: memory – Storage accessing and control – Memory configuring
Reexamination Certificate
2001-09-11
2004-12-14
Nguyen, T. N. (Department: 2187)
Electrical computers and digital processing systems: memory
Storage accessing and control
Memory configuring
C711S161000, C711S162000, C711S165000, C711S205000, C711S206000, C711S207000, C714S004110, C714S006130
Reexamination Certificate
active
06832301
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to a method for an operating system to reclaim or recover a subset of the resources of an address space in the case where the resources cannot be removed while the address space is active and more particularly to a more efficient method for an operating system to recover fixed real storage from a swappable address space.
BACKGROUND OF THE INVENTION
As used herein, the term ‘frame’ is meant to refer to a block of information, wherein the block of information may be the smallest allocatable unit of real storage.
As used herein, the term ‘fixed frame’ refers to a frame that cannot be taken or relocated except through the swap process.
As used herein, the term ‘fixed page’ refers to a virtual page backed by a fixed frame.
As used herein, the term ‘secondary storage’ refers to a location of a page when not residing in real memory.
As used herein, the term ‘frame table element’ or ‘frame element’ refers to the data structure representing a real frame, wherein each real frame has a frame table element.
Typically, in operating systems that support multiple virtual address spaces and that have the ability to fix certain blocks of information, or frames, in an address space in real memory for future use, the operating system is sometimes required to move fixed frames to an alternate memory location, such as a secondary memory or an expanded memory. This technique is called swapping and allows the operating system to reclaim a subset of the resource of the address space and use that subset for more immediate operations. The real memory for a page is allocated and the dynamic address translation tables for that page are updated using a process called ‘backing’, which indicates the real memory associated with that page.
Referring to
FIG. 1
, an operating system
300
is shown having multiple address spaces. Normally, each address space
302
contains a Region Control Task (RCT)
304
which controls various functions in the address space
302
, including the swapping process. In addition, each operating system includes a Real Storage Manager (RSM)
306
and a Systems Resource Manager (SRM)
308
which coordinate actions between the RCT
304
and any programs or applications
310
that are active. As an example, when stored information needs to be recovered from an address space
302
, the RSM
306
notifies the SRM
308
and the SRM
308
coordinates this action by communicating with the RCT
304
of the address space
302
. As another example, when a swappable address space
302
is to become non-swappable, the application
310
that initiates this action notifies the SRM
308
and the SRM
308
coordinates this by communicating with the RCT
304
and requesting that a swappable address space
302
become non-swappable.
In an operating system, real memory is categorized into preferred and non-preferred memory. Non-preferred memory is memory that can be made available on demand and preferred memory is memory that may hold long term fixed pages and that cannot be made available on demand. Swappable address spaces can fix pages in the preferred or non-preferred area of real memory and non-swappable address spaces can fix pages in the preferred area of real memory. Because non-preferred memory must be made available on demand the operating system must be able to recover (i.e. retrieve memory from an application using the memory) non-preferred memory when needed for more immediate operations. Typically, non-preferred memory must be recovered because the storage is to be configured offline or the address space owning the non-preferred memory is becoming long term non-swappable and hence all of its fixed frames must become preferred. Using current swapping methods, two processes, REQSWAP and TRANSWAP, are usually employed. The REQSWAP process is utilized for recovering fixed non-preferred memory from a swappable address space and the TRANSWAP process is utilized in systems which support the capability for the conversion of a swappable address space into non-swappable address space. Both the REQSWAP process and the TRANSWAP process facilitate the swapping action and are discussed in more detail below.
Referring to
FIG. 2
, the existing method for recovering swappable fixed non-preferred memory using the REQSWAP process is illustrated. If the operating system needs to configure a specific area of real memory, then the operating system sends a request to the Real Storage Manager (RSM) to configure an area of real memory offline as in step
100
. The RSM receives this request and determines which area of real memory will be configured as in step
102
. The RSM then indicates that this area of real memory has been ‘intercepted’ or ‘flagged’ to go offline as in step
104
. The RSM then determines if there are any fixed pages belonging to swappable address spaces contained within the range of real storage as in step
106
. If so, the operating system then swaps the entire address space to a secondary, or auxiliary storage, then back into real memory as in step
108
. This process of swapping the address space to an auxiliary storage will free the memory, thus allowing the ‘flagged’ frames to be available and thus configured offline.
One problem with this process is that every address space that contains fixed intercepted frames is swapped into a secondary memory storage or an external memory storage area which requires the need to perform Input/Output (I/O) operations. These I/O operations can be expensive in both time and cost.
Referring to
FIG. 3
, the existing method for recovering swappable fixed non-preferred memory where the originally swappable address space has been converted into non-swappable address space using the TRANSWAP process is illustrated. The operating system sends a request to the RSM to convert the address space with intercepted frames to non-swappable address space as in step
200
. The operating system then swaps the entire address space to a secondary or auxiliary memory storage area as in step
202
. The SRM will then send a request to the RSM to swap in the address space as in step
204
. In swapping the address space back into real memory, the operating system will detect that the address space is now non-swappable and will allocate preferred memory for all fixed pages with the address space as in step
206
. The entire address space is swapped which is a time consuming and expensive process.
Currently, the only method for recovering fixed non-preferred frames is to swap the entire owning address space to secondary storage. However, two problems exist with these methods. First, in an operating system that doesn't support expanded storage (such as an electronic volatile storage comparable to real storage), all swapped non-preferred memory is required to be relocated to a secondary or auxiliary memory location. This is undesirable because a swap out to a secondary or auxiliary storage location is much more expensive than a swap out to an expanded storage location. Second, all of the frames in the address space must be processed in order to perform the swap even though only a subset of the frames actually need to be replaced. In effect, the way the REQSWAP and TRANSWAP processes perform their tasks is inherently costly and inefficient. Thus, it is desirable to provide a method which is capable of performing the tasks of REQSWAP and TRANSWAP, yet that is more efficient and less expensive to implement.
Therefore, the need remains for a method of recovering fixed non-preferred memory whereby the method is more efficient and less expensive to implement than current swapping methods.
SUMMARY OF THE INVENTION
In a computing system having swappable and non-swappable address spaces, wherein the computing system includes an operating system that includes a Real Storage Manager (RSM), a Systems Resource Manager (SRM) and a Region Control Task (RCT), a method for recovering swappable fixed non-preferred memory comprising: receiving a request from the operating system to configure an area of real memory to create an int
Bobak Roman A.
Mari Charles E.
Morgenstern Harris
Mulder Jim H.
Rogers Robert R.
Cantor & Colburn LLP
International Business Machines - Corporation
Kinnaman, Jr. William A.
Nguyen T. N.
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