APPARATUS, SYSTEM, AND METHOD FOR MANAGING CONTENTS OF A CACHE

• US 20120221774A1
• Filed: 02/27/2012
• Published: 08/30/2012
• Est. Priority Date: 02/25/2011
• Status: Active Grant

• Current Assignee: SanDisk Technologies LLC (Western Digital Corporation)
• Original Assignee: Fusion-IO Incorporated (Western Digital Corporation)
• Inventors: Atkisson, David, Flynn, David
• Granted Patent: US 9,141,527 B2
• Time in Patent Office: Days
• US Class Current: 711/103
• CPC Class Codes: G06F 12/0246 in block erasable memory, e.g. flash memory
• CPC Class Codes: G06F 12/0802 Addressing of a memory level in which the access to the desired data or data block requires associative addressing means, e.g. caches
• CPC Class Codes: G06F 12/0895 of parts of caches, e.g. directory or tag array
• CPC Class Codes: G06F 12/126 with special data handling, e.g. priority of data or instructions, handling errors or pinning
• CPC Class Codes: G06F 2212/601 Reconfiguration of cache memory

Abstract

An apparatus, system, and method are disclosed for managing contents of a cache. A storage request module monitors storage requests received by a cache. The storage requests include read requests and write requests. A read pool module adjusts a size of a read pool of the cache to maximize a read hit rate of the storage requests. A dirty write pool module adjusts a size of a dirty write pool of the cache to maximize a dirty write hit rate of the storage requests.

Claims

1. A method for managing contents of a cache, the method comprising:

monitoring storage requests received by a cache, the storage requests comprising read requests and write requests;

adjusting a size of a read pool of the cache to maximize a read hit rate of the storage requests; and

adjusting a size of a dirty write pool of the cache to maximize a dirty write hit rate of the storage requests.

2. The method of claim 1, further comprising determining a target read pool size for the read pool and a target dirty write pool size for the dirty write pool based on the monitored storage requests received by the cache.

3. The method of claim 2, wherein adjusting the size of the read pool comprises selecting data for eviction from the cache based at least partially on a difference between an actual read pool size and the target read pool size.

4. The method of claim 3, wherein the read pool of the cache comprises a recent read pool and a frequent read pool and adjusting the size of the read pool further comprises increasing a target recent read pool size of the recent read pool in response to a read hit in the recent read pool, requested data transitioning from the recent read pool to the frequent read pool in response to a frequent read threshold number of read hits for the requested data in the recent read pool.

5. The method of claim 3, wherein adjusting the size of the read pool further comprises reducing the target read pool size in response to a read miss, the actual size of the read pool increasing in response to caching data of the read miss in the cache.

6. The method of claim 2, wherein adjusting the size of the dirty write pool of the cache comprises destaging dirty write data from the dirty write pool of the cache at a destage rate, the destage rate based on a difference between an actual dirty write pool size and the target dirty write pool size.

7. The method of claim 6, further comprising setting the destage rate such that the size of the dirty write pool remains within a maximum dirty write pool size of the dirty write pool.

8. The method of claim 6, wherein adjusting the size of the dirty write pool further comprises increasing the target dirty write pool size in response to a dirty write hit.

9. The method of claim 6, wherein adjusting the size of the dirty write pool further comprises increasing the target dirty write pool size in response to a clean write hit.

10. The method of claim 6, wherein adjusting the size of the dirty write pool further comprises decreasing the target dirty write pool size in response to a write miss, the actual size of the dirty write pool increasing in response to servicing a write request of the write miss.

11. The method of claim 1, wherein the read pool of the cache comprises a recent read pool and a frequent read pool and adjusting the size of the read pool comprises adjusting a size of the recent read pool to maximize the read hit rate of the storage requests.

12. The method of claim 11, wherein adjusting the size of the read pool further comprises adjusting a size of the frequent read pool to maximize the read hit rate of the storage requests.

13. The method of claim 1, further comprising adjusting a size of a clean write pool of the cache to maximize the read hit rate and the dirty write hit rate of the storage requests.

14. The method of claim 13, wherein adjusting the size of the clean write pool of the cache comprises adjusting a destage rate at which data is moved from the dirty write pool to the clean write pool to maximize the dirty write hit rate and adjusting an eviction rate at which data is evicted from the clean write pool to maximize the read hit rate.

15. The method of claim 1, further comprising,

reading requested data from the cache to service a read request;

and

writing the requested data forward on a sequential log-based writing structure of the cache in response to the read request.

16. The method of claim 15, wherein the read request satisfies a frequent read threshold number of read hits for the requested data, the requested data transitioning from a recent read pool of the read pool to a frequent read pool of the read pool in response to the read request.

17. The method of claim 1, further comprising maintaining metadata for evicted data, the evicted data comprising read data from the read pool and clean write data destaged from the dirty write pool.

18. The method of claim 17, wherein the metadata comprises one or more entries for the evicted data in a mapping structure, the mapping structure mapping logical addresses of the cache to locations on physical storage media of the cache.

19. The method of claim 18, wherein the metadata for the evicted data indicates that the physical storage media of the cache does not currently store the evicted data.

20. The method of claim 17, further comprising adding the evicted data to a frequent read pool of the read pool of the cache, based on the metadata for the evicted data, in response to a subsequent read request for the evicted data.

21. An apparatus for managing contents of a cache, the apparatus comprising:

a storage request module that monitors storage requests received by a cache, the storage requests comprising read requests and write requests;

a read pool module that determines a target read pool size for a read pool of the cache based on the monitored storage requests;

an eviction module that selects data for eviction from the cache based at least partially on a difference between an actual read pool size and the target read pool size;

a dirty write pool module that determines a target dirty write pool size for a dirty write pool of the cache based on the monitored storage requests; and

a destage module that adjusts a destage rate for destaging dirty write data from the dirty write pool of the cache, the destage module adjusting the destage rate based on a difference between an actual dirty write pool size and the target dirty write pool size.

22. The apparatus of claim 21, further comprising a clean write pool module that determines a target clean write pool size for a clean write pool of the cache based on the monitored storage requests, wherein the eviction module selects the data for eviction from the cache based at least partially on a difference between an actual clean write pool size and the target clean write pool size.

23. The apparatus of claim 21, wherein the read pool comprises a recent read pool and a frequent read pool, the target read pool size comprises a target recent read pool size and a target frequent read pool size, and the eviction module selects the data for eviction from the cache based at least partially on a difference between an actual recent read pool size and the target recent read pool size and a difference between an actual frequent read pool size and the target frequent read pool size.

24. A system for managing contents of a cache, the system comprising:

a processor;

a storage controller for a nonvolatile solid-state storage device, the nonvolatile solid-state storage device in communication with the processor over one or more communications buses;

a cache controller in communication with the storage controller, the cache controller comprising,

a storage request module that monitors storage requests received by the cache controller, the storage requests comprising read requests and write requests;

a read pool module that adjusts a size of a read pool of the cache to maximize a read hit rate of the storage requests; and

a dirty write pool module that adjusts a size of a dirty write pool of the cache to maximize a dirty write hit rate of the storage requests.

25. The system of claim 24, further comprising a host computer system, the host computer system comprising the processor, wherein the storage controller and the cache controller comprise one or more device drivers executing on the processor of the host computer system.