Virtual memory structure

Details Virtual memory structure Virtual memory structure

2001-02-28

2003-09-16

Sparks, Donald (Department: 2186)

Electrical computers and digital processing systems: memory

Address formation

Address mapping

C711S205000, C711S206000, C711S207000

Reexamination Certificate

active

06622229

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention relates generally to memory management in computer systems and in particular to a virtual memory space that includes a separate space for a page frame table (PFT). For any computer system supporting multiple address spaces, it is necessary for the operating system to manage each allocatable unit of real storage. Such an allocatable unit of real storage may be referred to as a frame. To manage frames of real memory, some data structure is typically used to represent the status of each frame. Status information may include the process currently using the frame, the virtual address that the frame is backing (if applicable), when the frame was last referenced and whether the frame is online. Backing refers to a virtual storage concept where a frame contains the data that a virtual address refers to and the connection between the virtual address and the frame is through segment and page tables, usually referred to as dynamic address translation (DAT) structures.
For example, in the OS/390® operating system, a page frame table entry (PFTE) represents a real frame in the system. The aggregate of the PFTEs is referred to as the page frame table or PFT.
FIG. 1
depicts a conventional placement of the PFT in a virtual memory space
10
. As shown in
FIG. 1
, the PFT
12
resides within the common area
14
of every virtual address space in the system so that it is readily accessible to every process. Also included in the virtual address space
10
are private areas
16
used by specific processes in the system. A drawback to this approach is that as the size of real storage grows, the size of the PFT and the common area grows with it, effectively reducing the amount of virtual storage left for private areas in each virtual address space.
SUMMARY OF THE INVENTION
An exemplary embodiment of the invention is a virtual memory structure having a first virtual memory space and a virtual page frame table space. The first virtual memory space includes at least one private area and at least one common area. The virtual page frame table space is separate from the first virtual memory space. The virtual page frame table space includes at least one page frame table entry representing a frame of real memory.


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