COMBINING MEMORY PAGES HAVING IDENTICAL CONTENT

• US 20120246436A1
• Filed: 03/21/2011
• Published: 09/27/2012
• Est. Priority Date: 03/21/2011
• Status: Active Grant

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Corporation
• Inventors: Wang, Landy, Iyigun, Mehmet, Bak, Yevgeniy, Sundaram, Vijay, Lebedynskiy, Pavlo L.
• Granted Patent: US 9,058,212 B2
• Time in Patent Office: Days
• US Class Current: 711/170
• CPC Class Codes: G06F 12/109 for multiple virtual address spaces, e.g. segmentation G06F12/1036 takes precedence
• CPC Class Codes: G06F 9/5016 the resource being the memory

Abstract

In a device having a memory accessed as multiple pages, two or more pages of the multiple pages having identical content are identified. While the two or more pages are being identified, other processes running in the device are allowed to use the two or more pages, including being allowed to change cache attributes of each of the two or more pages. The two or more pages are combined into a single combined page (e.g., a newly allocated page of the multiple pages), and a process page record having multiple entries pointing to the multiple pages is updated so that entries that previously pointed to one of the two or more pages instead point to the single page.

Claims

1. A method in a device having a memory accessed as multiple pages, the method comprising:

identifying two or more pages of the multiple pages having identical content;

allowing, while the two or more pages are being identified, other processes running on the device to use the two or more pages including allowing the other processes to change cache attributes of each of the two or more pages;

combining the two or more pages into a single combined page; and

updating a process page record having multiple entries pointing to the multiple pages so that entries that previously pointed to one of the two or more pages instead point to the single combined page.

2. A method as recited in claim 1, the other processes being unaware of the identifying, combining, and updating.

3. A method as recited in claim 1, the allowing comprising:

ceasing analyzing a page to determine whether the page may have identical content as one or more other pages of the multiple pages in response to a request that can potentially result in a memory coherency or corruption situation being received while analyzing the page; and

allowing the request to be performed.

4. A method as recited in claim 1, further comprising performing the identifying, allowing, combining, and updating in response to an indication from a user mode page combine policy module to analyze the multiple pages.

5. A method as recited in claim 4, the user mode page combine policy module generating the indication based at least in part on various aspects of the device that are monitored by the page combine policy module.

6. A method as recited in claim 1, the combining comprising allocating a new page of the memory as the single combined page, and the updating the process page record comprising updating the process page record so that each entry that previously pointed to one of the two or more pages instead points to the new page.

7. A method as recited in claim 6, the new page being allocated in a way that reduces physical memory fragmentation.

8. A method as recited in claim 1, the identifying comprising:

generating, for each of the multiple pages, a cyclic redundancy check (CRC) value;

identifying ones of the multiple pages having matching CRC values; and

comparing the ones of the multiple pages having matching CRC values to determine which of the ones, if any, have identical content.

9. A method as recited in claim 8, the multiple pages including previously combined pages.

10. A method as recited in claim 9, the previously combined pages including one or more previously combined pages that have been transferred to a storage device.

11. A method as recited in claim 1, further comprising, in response to a request from one of the other processes to write to a memory address included in one of the two or more pages:

allocating a new page in the memory;

copying the content of the single combined page to the new page; and

updating the process page record so that an entry for the process from which the request was received that previously pointed to the combined page instead points to the new page.

12. A method as recited in claim 11, further comprising

repeating the allocating, copying, and updating the process page record in response to each of multiple additional write requests to memory addresses included in one of the two or more pages;

and

de-allocating the combined page when a reference count indicates that no more process page record entries point to the combined page.

13. One or more computer storage media having stored thereon multiple instructions that, when executed by one or more processors of a device having a memory accessed as multiple pages, implement a page combination procedure by causing the one or more processors to:

identify two or more pages of the multiple pages having identical content;

allocate a new page of the multiple pages, the new page having the identical content as the two or more pages; and

update a process page record having multiple entries pointing to the multiple pages so that entries that previously pointed to one of the two or more pages instead point to the new page.

14. One or more computer storage media as recited in claim 13, one or more additional processes running on the device other than a process implementing the page combination procedure being unaware of the identification, allocation, and updating.

15. One or more computer storage media as recited in claim 13, wherein to identify two or more pages is to:

generate, for each of the multiple pages, a cyclic redundancy check (CRC) value;

identify ones of the multiple pages having matching CRC values; and

compare the ones of the multiple pages having matching CRC values to determine which of the ones, if any, have identical content.

16. One or more computer storage media as recited in claim 15, the multiple pages including previously combined pages.

17. One or more computer storage media as recited in claim 16, the previously combined pages including one or more previously combined pages that have been transferred to a storage device.

18. One or more computer storage media as recited in claim 13, wherein the instructions further cause the one or more processors to, in response to a request to write to a memory address included in one of the two or more pages:

allocate an additional new page in the memory;

copy the content of the new page to the additional new page; and

update the process page record so that an entry for a process from which the request was received that previously pointed to the new page instead points to the additional new page.

19. One or more computer storage media as recited in claim 13, the new page being allocated in a way that reduces physical memory fragmentation.

20. A method in a device having a memory accessed as multiple pages, the method comprising:

determining, in response to an indication received from a user mode page combine policy module, to perform a page combination procedure;

identifying, as part of the page combination procedure, two or more pages of the multiple pages having identical content, the multiple pages including previously combined pages that have been transferred to a storage device;

allowing, while the two or more pages are being identified, other processes running on the device to use the two or more pages including allowing the other processes to change cache attributes of each of the two or more pages;

combining, as part of the page combination procedure, the two or more pages into a single combined page by allocating a new page of the multiple pages and copying the content of one of the two or more pages to the new page; and

updating, as part of the page combination procedure, a process page record having multiple entries pointing to the multiple pages so that entries that previously pointed to one of the two or more pages instead point to the single combined page.