US 4,742,447 A · Method to control I/O accesses in a multi-tasking virtual memory virtual machine type data processing system

Abstract

A method for accessing information in a page segmented virtual memory data processing system in which virtual machines running UNIX type operating systems are concurrently established, and in which a memory manager controls the transfer of information between primary and secondary storage devices in response to the occurrence of page faults. The method establishes a plurality of data structures in a dynamic manner in response to a Supervisor call to "map" a file. The mapping process assigns a new segment of virtual memory to the mapped file and correlates, in one data structure, the virtual address of each page of data in the new segment to a disk file address where that page is actually stored. A UNIX system call by an application program for a specific virtual page is handled by the page fault hanger, and not the UNIX kernel, since the application can supply the real address of the page on the disk file from the data structure that was created by the mapped page range Supervisor call. Simple load and store type of instructions are employed for the data transfer, which avoids much of the overhead that normally accompanies conventional UNIX read and write system calls to the storage subsystem.

A method for a page segmented virtual memory data processing system having

(1) a main memory including
a first plurality of byte addressable storage locations each of which functions to store one byte of data,
(2) a secondary storage device including
a second plurality of block addressable storage locations each of which functions to store at least one virtual page of data,
(3) a resource manager for creating at least one machine having a UNIX type Operating System {UOS} program which includes,
(a) conventional Unix commands for opening and creating new Unix files,
(b) I/O commands for transferring Unix file data between said device and said main memory, said I/O commands each including,
(i) a file descriptor parameter,
(ii) a buffer pointer parameter, and
(iii) a parameter specifying the number of bytes of data that is to be transferred by each of said commands,
(c) means for storing a Unix offset pointer which designates a byte location in said device from which or to which said file data is transferred by each of said I/O commands, and
(d) I/O subroutines which are run when said I/O commands are executed,
(4) an application program which includes conventional Unix I/O system calls to said I/O commands, and
(5) a memory manager program having,
(a) Load and Store type of instructions each employing a virtual page address for transferring a page of data between said device and said main memory,
(b) a pageable External Page Table {XPT} for relating each said virtual page address to a different one of said block addressable locations,
(c) a non-pageable Internal Page Table {IPT} for relating virtual page addresses to byte addressable locations in said device,
(d) a page fault handling mechanism for resolving a page fault that occurs as a result of said application program executing an instruction involving a virtual page which is not currently stored in said main memory, said mechanism causing said one involved virtual page to be transferred to said device by referencing said XPT to relate said involved virtual page address to a block address where said page is stored,
said method causing said data transfers defined in said I/O system calls to be made under the control of said memory manager and said page fault handling mechanism, rather than said I/O subroutines of said UOS, said method comprising the steps of,
(A) creating a new instruction for said operating system which functions to map a specified Unix file stored in said device to new virtual page addresses in another segment of said virtual memory so as to relate the newly assigned virtual page addresses in said another segment to said corresponding block address in said device,
(B) mapping said specified Unix file to assign said new virtual page addresses in said another segment by executing said new instruction, including the steps of;
(a) establishing a first data structure for storing said map, said first data structure having an entry for each active page of said specified Unix file, each entry including a first field which stores said block address of one said active page and a second field which stores one of said new virtual page addresses in said another segment,
(b) assigning a virtual address to said first data structure from a predetermined segment of said virtual memory,
(c) storing said first data structure in said device, and
(C) dynamically generating another virtual page address within the address range of said another segment during execution of each said I/O commands by translating at least one of said command parameters and said offset point for said specified file to said another virtual page address which is then employed with said first data structure by said memory manager and fault handling mechanism to transfer the virtual pages containing said file data specified by at least one of said parameters, between said main memory and said storage device.

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Method to control I/O accesses in a multi-tasking virtual memory virtual machine type data processing system

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Method to control I/O accesses in a multi-tasking virtual memory virtual machine type data processing system

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Abstract

Claims17