Method and apparatus for memory-mapped input/output

• US 20050268067A1
• Filed: 05/28/2004
• Published: 12/01/2005
• Est. Priority Date: 05/28/2004
• Status: Active Grant

• Current Assignee: Oracle International Corporation (Oracle Corporation)
• Original Assignee: Oracle International Corporation (Oracle Corporation)
• Inventors: Lee, Robert, Sexton, Harlan
• Granted Patent: US 7,383,414 B2
• Time in Patent Office: Days
• US Class Current: 711/202
• CPC Class Codes: G06F 12/10 Address translation

Abstract

A method of managing memory mapped input/output (I/O) for a run-time environment is disclosed, in which opaque references are used for accessing information blocks included in files used in a dynamic run-time environment. The information block is stored in a shared memory space of pages that are each aligned on respective boundaries having addresses that are each some multiple of two raised to an integer power. The opaque reference used for the dynamic run-time environment includes at least an index, or page number reference into a page map of references to the pages of the shared memory space, and an offset value indicating an offset into the referenced page for the beginning of the storage of the information block. Control bits of the opaque reference indicate information such as the mapping mode, e.g., read-only, read-write, or private. Pages which are modified by a process may be written back to a backing store of the file based on control bits which indicate that a page has been modified.

Claims

1. A method of reading a block of data at a location in a memory-mapped file, comprising the steps of:

receiving a reference indicating the location in the memory-mapped file;

extracting a page number and a page offset from respective portions of the reference;

computing a shared memory address in main memory based on the page number and the page offset; and

reading the block of data from a paged memory indicated at the shared memory address.

2. The method according to claim 1, wherein the memory-mapped file corresponds to a file stored in a secondary storage used by a process, and at least a portion of the file used by the process is copied into the main memory for accessibility by the process.

3. The method according to claim 2, wherein the shared memory address in main memory is accessible to another process.

4. The method according to claim 1, wherein said computing includes:

fetching a memory address of a page from a page map at an index indicated by the page number; and

adding the page offset to the memory address of the page to produce the shared memory address.

5. The method according to claim 4, further comprising loading a portion of the memory-mapped file corresponding to the page from secondary storage into the address space before performing said reading the number of bytes from the shared memory.

6. The method according to claim 5, further comprising loading the portion after said receiving the reference.

7. The method according to claim 1, wherein said reading includes reading the number of bytes from the shared memory from at least two pages of the shared memory.

8. A computer-readable medium bearing instructions for reading a number of bytes at a location in a memory-mapped file, said instructions being arranged, upon execution, to cause one or more processors to perform the step of a method according to claim 1.

9. A method of writing a number of bytes to a location in a memory-mapped file, comprising the steps of:

receiving a reference indicating the location in the memory-mapped file;

extracting a page number and a page offset from respective portions of the reference;

computing a shared memory address based on the page number and the page offset; and

writing the number of bytes to a shared memory indicated at the shared memory address.

10. The method according to claim 9, wherein the memory-mapped file corresponds to a file stored in a secondary storage used by a process, and at least a portion of the file used by the process is copied into the main memory for accessibility by the process.

11. The method according to claim 10, wherein the shared memory address in main memory is accessible to another process.

12. The method according to claim 9, wherein said computing includes:

fetching a memory address of a page from a page map at an index indicated by the page number; and

adding the page offset to the memory address of the page to produce the shared memory address.

13. The method according to claim 12, further comprising loading a portion of the memory-mapped file corresponding to the page from secondary storage into the shared memory before performing said writing the number of bytes to the shared memory.

14. The method according to claim 13, further comprising loading the portion after receiving the reference.

15. The method according to claim 9, wherein said writing includes writing the number of bytes to the shared memory indicated at the shared memory address to at least two pages of the shared memory.

16. A computer-readable medium bearing instructions for writing a number of bytes to a location in a memory-mapped file, said instructions being arranged, upon execution, to cause one or more processors to perform the step of a method according to claim 9.

17. A method of memory-mapping a file, the method comprising the steps of:

determining an available page in a shared memory space for storing at least a portion of the file;

computing a shared page reference to the available page based on a memory address of the available page and control information associated with the available page;

storing the shared page reference in a page map;

storing the at least a portion of the file in the available page; and

computing an opaque reference to the available page indicating a page map index for the location of the shared page reference and an offset value.

18. The method according to claim 17, wherein the memory-mapped file corresponds to a file stored in a secondary storage used by a process, and at least a portion of the file used by the process is copied into the main memory for accessibility by the process.

19. The method according to claim 18, wherein the shared memory address in main memory is accessible to another process.

20. The method according to claim 17, wherein said computing includes:

determining the page map index for the location of the shared page reference in the page map; and

masking the page map index with the offset value to produce the opaque reference.

21. The method according to claim 20, further comprising accessing a portion of the memory-mapped file using the opaque reference.

22. The method according to claim 17, further comprising storing a plurality of portions of the file in a plurality of pages in the shared memory space.

23. The method according to claim 17, further comprising:

determining another available page in the shared memory space for storing another portion of the file;

computing an other shared page reference to the another available page based on a memory address of the another available page and control information associated with the another available page;

storing the other shared page reference in the page map in storage adjacent to storage of the shared page reference; and

storing the another portion of the file in the another available page.

24. A computer-readable medium bearing instructions for memory-mapping a file, said instructions being arranged, upon execution, to cause one or more processors to perform the step of a method according to claim 17.