Asynchronous swap mechanism and page eviction from memory

• US 9,400,754 B2
• Filed: 12/19/2013
• Issued: 07/26/2016
• Est. Priority Date: 12/19/2013
• Status: Active Grant

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Hopper, Jenifer, Peloquin, Mark A., Pratt, Steven L., Rister, Karl M.
• Primary Examiner(s): Bradley, Matthew
• Assistant Examiner(s): Perez-Velez, Rocio Del Mar
• Application Number:
  US14/134,365
• Publication Number:
  US 20150178222A1
• Time in Patent Office: 950 Days
• US Class Current: 1/1
• CPC Class Codes: G06F 12/121 using replacement algorithms
• CPC Class Codes: G06F 2212/401 Compressed data
• CPC Class Codes: G06F 3/0619 in relation to data integrity, e.g. data losses, bit errors
• CPC Class Codes: G06F 3/065 Replication mechanisms
• CPC Class Codes: G06F 3/067 Distributed or networked storage systems, e.g. storage area networks [SAN], network attached storage [NAS]

Abstract

Embodiments of the invention relate to mitigating page eviction from cache memory. Pages of data in the cache are compressed, and are periodically swapped to a physical storage device to create space in the cache for additional pages. To avoid the impact of eviction latencies, an asynchronous thread scanning process scans the cache for any pages that are not committed to the storage device, decompresses a selected one of the pages, and asynchronously writes the decompressed page copy to the physical storage device. The compressed copy of the selected page remains in the cache during the asynchronous write with an indicator for the page set to convey that a replica of the page has been written to physical storage, allowing for efficient eviction from the in-memory pool at a later time.

Claims

1. A method comprising:

scanning a random access memory device for one or more compressed pages of memory uncommitted to a physical storage device;

selecting at least one uncommitted page from the random access memory device;

creating a replica of the selected uncommitted page, including copying the selected uncommitted page, and decompressing the copy; and

asynchronously writing the replica to the physical storage device, and setting a replica indicator on the selected uncommitted page while the selected uncommitted page remains in the random access memory device.

2. The method of claim 1, wherein the selected uncommitted page remains in the random access memory device during the asynchronous writing of the replica to the physical storage device.

3. The method of claim 2, further comprising determining that the random access memory device exceeds a capacity in response to selecting a new page of memory for storage in the random access memory device, and scanning the memory device for at least one eligible page.

4. The method of claim 3, wherein determining that the random access memory device is unable to store the new page comprises determining that the random access memory device has reached capacity.

5. The method of claim 3, further comprising removing the at least one eligible page from the random access memory device, and storing the new page in the random access memory device.

6. The method of claim 5, wherein the new page is uncompressed, and further comprising:

compressing the new page prior to the storage in the random access memory device;

reserving a slot for the new page on the physical storage device.

determining that at least one selected eligible page is uncommitted; and

writing a replica of each uncommitted selected eligible page to the physical storage device prior to the removal from the random access memory device.

7. The method of claim 5, further comprising determining that at least one of the scanned eligible pages has a replica indicator, wherein the removed eligible page is an eligible page determined to have a replica indicator.

8. The method of claim 1, wherein the replica indicator is a flag indicating that the replica is on the physical storage device.

9. A computer program product for managing a random access memory device, the computer program product comprising a computer readable storage device having program code embodied therewith, the program code executable by a processor to:

scan the random access memory device for one or more compressed pages of memory uncommitted to a physical storage device;

select at least one uncommitted page from the random access memory device;

create a replica of the selected uncommitted page, including program code to copy the selected uncommitted page, and decompress the copy;

asynchronously write the replica to the physical storage device, and set a replica indicator on the selected uncommitted page while the selected uncommitted page remains in the random access memory device.

10. The computer program product of claim 9, wherein the selected uncommitted page remains in the random access memory device during the asynchronous writing of the replica to the physical storage device.

11. The computer program product of claim 10, further comprising program code to determine that the random access memory device exceeds a capacity in response to a selection of a new page of memory for storage in the random access memory device, and scan the memory device for at least one eligible page.

12. The computer program product of claim 11, further comprising program code to remove the at least one eligible page from the memory device, and store the new page in the random access memory device.

13. The computer program product of claim 12, wherein the new page is uncompressed, and further comprising program code to:

compress the new page prior to the storage in the random access memory device;

reserve a slot for the new page on the physical storage device;

determine that at least one selected eligible page is uncommitted;

write a replica of each uncommitted selected eligible page to the physical storage device prior to the removal from the random access memory device.

14. The system of claim 12, wherein the new page is uncompressed, and wherein the swap further comprises:

the manager to compress the first page prior to storage in the random access memory device, and reserve a slot for the new page on the physical storage device;

the scanner to determine that at least one selected eligible page is uncommitted; and

the manager to write a replica of each uncommitted selected eligible page to the physical storage device prior to the removal from the random access memory device.

15. The computer program product of claim 9, wherein the replica indicator is a flag indicating that the replica is on the physical storage device.

16. A computer system comprising:

a processing unit operatively coupled to a random access memory device;

a physical storage device in communication with the random access memory device; and

tools in communication with the processing unit to manage the random access memory device, including;

a scanner to scan the random access memory device for one or more compressed pages of memory uncommitted to the physical storage device;

a selector in communication with the scanner, the selector to select at least one uncommitted page from the memory device;

a manager in communication with the selector, the manager to;

create a replica of the selected uncommitted page, including the manager to copy the selected uncommitted page, and decompress the copy; and

asynchronously write the replica to the physical storage device, and set a replica indicator on the selected uncommitted page while the selected page remains in the random access memory device.

17. The system of claim 16, wherein the selected uncommitted page remains in the random access memory device during the asynchronous writing of the replica to the physical storage device.

18. The system of claim 17, further comprising the manager to determine that the random access memory device exceeds a capacity in response to a selection of a new page of memory for storage in the random access memory device, and the scanner scan the random access memory device for at least one eligible page.

19. The system of claim 18, further comprising the manager to remove the at least one eligible page from the random access memory device, and store the new page in the random access memory device.

20. The system of claim 16, wherein the replica indicator is a flag to indicate that the replica is on the physical storage device.