Balancing allocated cache pages among storage devices in a flash cache
View Patent ↗Described herein are techniques for use in balancing allocated cache pages among storage devices in a flash cache. The techniques comprise determining an expected number of allocated cache pages in connection with a non-volatile storage device that forms at least part of a flash cache. The techniques also comprise performing a comparison between the expected number of allocated cache pages and an actual number of allocated or free cache pages in connection with the non-volatile storage device. The techniques further comprise selecting, based on the comparison, a free cache page in connection with the non-volatile storage device to allocate as a cache page.
1. A computer-implemented method, comprising:
determining an expected number of allocated cache pages in connection with a non-volatile storage device that forms at least part of a flash cache;
performing a comparison between the expected number of allocated cache pages and an actual number of allocated or free cache pages in connection with the non-volatile storage device; and
based on the comparison, selecting a free cache page in connection with the non-volatile storage device to allocate as a cache page, to balance the allocated or free cache pages among a plurality of non-volatile storage devices that form the flash cache, wherein the non-volatile storage device is one of the plurality of non-volatile storage devices that forms the flash cache; and wherein determining the expected number of allocated cache pages in connection with the non-volatile storage device comprises: forming a first value relating to available cache storage associated with the non-volatile storage device; forming a second value relating to available cache storage associated with the flash cache; forming a ratio of the first value to the second value to produce a third value; forming a fourth value relating to an actual number of allocated cache pages in connection with the flash cache; and forming a product of the third and fourth values to produce the expected number of allocated cache pages in connection with the non-volatile storage device.
2. The method as claimed in claim 1 , wherein the non-volatile storage device is one of the plurality of non-volatile storage devices that forms the flash cache; and
wherein the method further comprises:
receiving a write I/O relating to a cache page in connection with another non-volatile storage device of the plurality of non-volatile storage devices that forms the flash cache;
performing a second comparison between the expected number of allocated cache pages and an actual number of allocated or free cache pages in connection with the another non-volatile storage device;
based on the second comparison, writing data associated with the write I/O to the selected cache page in connection with the non-volatile storage device; and
sending a command to free the cache page in connection with the another non-volatile storage device.
3. The method as claimed in claim 1 , wherein the non-volatile storage device is one of the plurality of non-volatile storage devices that forms the flash cache; and
wherein the method further comprises:
receiving data that is one of promoted or demoted to the flash cache; and
storing the data in the selected cache page in connection with the non-volatile storage device of the plurality of non-volatile storage devices that forms the flash cache.
4. The method as claimed in claim 1 , wherein the non-volatile storage device is one of the plurality of non-volatile storage devices that forms the flash cache; and
wherein the method further comprises:
detecting an intention to remove one of the plurality of non-volatile storage devices from the flash cache; and
moving data associated with a cache page in connection with the one of the plurality of non-volatile storage devices to the selected cache page.
5. The method as claimed in claim 1 , wherein the actual number corresponds to the amount of allocated cache pages in connection with the non-volatile storage device; and
wherein performing the comparison, comprises:
determining if the expected number of allocated cache pages is greater or less than the actual number of allocated cache pages in connection with the non-volatile storage device; and
in response to determining the expected number is greater than the actual number, determining to select a free cache page in connection with the non-volatile storage device to allocate as a cache page.
6. The method as claimed in claim 1 , wherein the actual number corresponds to the amount of free cache pages in connection with the non-volatile storage device; and
wherein performing the comparison, comprises:
determining if the expected number of allocated cache pages is greater or less than the actual number of free cache pages in connection with the non-volatile storage device; and
in response to determining the expected number is less than the actual number, determining to select a free cache page in connection with the non-volatile storage device to allocate as a cache page.
7. An apparatus, comprising:
memory; and
processing circuitry coupled to the memory, the memory storing program code which, when executed by the processing circuitry, cause the processing circuitry to:
determine an expected number of allocated cache pages in connection with a non-volatile storage device that forms at least part of a flash cache;
perform a comparison between the expected number of allocated cache pages and an actual number of allocated or free cache pages in connection with the non-volatile storage device; and
based on the comparison, select a free cache page in connection with the non-volatile storage device to allocate as a cache page, to balance the allocated or free cache pages among a plurality of non-volatile storage devices that form the flash cache, wherein the non-volatile storage device is one of the plurality of non-volatile storage devices that forms the flash cache; and wherein determining the expected number of allocated cache pages in connection with the non-volatile storage device comprises: forming a first value relating to available cache storage associated with the non-volatile storage device; forming a second value relating to available cache storage associated with the flash cache; forming a ratio of the first value to the second value to produce a third value; forming a fourth value relating to an actual number of allocated cache pages in connection with the flash cache; and forming a product of the third and fourth values to produce the expected number of allocated cache pages in connection with the non-volatile storage device.
8. The apparatus as claimed in claim 7 , wherein the non-volatile storage device is one of the plurality of non-volatile storage devices that forms the flash cache; and
wherein the memory stores program code which, when executed by the processing circuitry, cause the processing circuitry to:
receive a write I/O relating to a cache page in connection with another non-volatile storage device of the plurality of non-volatile storage devices that forms the flash cache;
perform a second comparison between the expected number of allocated cache pages and an actual number of allocated or free cache pages in connection with the another non-volatile storage device;
based on the second comparison, write data associated with the write I/O to the selected cache page in connection with the non-volatile storage device; and
send a command to free the cache page in connection with the another non-volatile storage device.
9. The apparatus as claimed in claim 7 , wherein the non-volatile storage device is one of the plurality of non-volatile storage devices that forms the flash cache; and
wherein the memory stores program code which, when executed by the processing circuitry, cause the processing circuitry to:
receive data that is one of promoted or demoted to the flash cache; and
store the data in the selected cache page in connection with the non-volatile storage device of the plurality of non-volatile storage devices that forms the flash cache.
10. The apparatus as claimed in claim 7 , wherein the non-volatile storage device is one of the plurality of non-volatile storage devices that forms the flash cache; and
wherein the memory stores program code which, when executed by the processing circuitry, cause the processing circuitry to:
detect an intention to remove one of the plurality of non-volatile storage devices from the flash cache; and
move data associated with a cache page in connection with the one of the plurality of non-volatile storage devices to the selected cache page.
11. The apparatus as claimed in claim 7 , wherein the actual number corresponds to the amount of allocated cache pages in connection with the non-volatile storage device; and
wherein performing the comparison, comprises:
determining if the expected number of allocated cache pages is greater or less than the actual number of allocated cache pages in connection with the non-volatile storage device; and
in response to determining the expected number is greater than the actual number, determining to select a free cache page in connection with the non-volatile storage device to allocate as a cache page.
12. The apparatus as claimed in claim 7 , wherein the actual number corresponds to the amount of free cache pages in connection with the non-volatile storage device; and
wherein performing the comparison, comprises:
determining if the expected number of allocated cache pages is greater or less than the actual number of free cache pages in connection with the non-volatile storage device; and
in response to determining the expected number is less than the actual number, determining to select a free cache page in connection with the non-volatile storage device to allocate as a cache page.
13. A computer program product having a non-transitory computer readable medium which stores a set of instructions, the set of instructions, when carried out by processing circuitry, causing the processing circuitry to perform a method, the method comprising:
determining an expected number of allocated cache pages in connection with a non-volatile storage device that forms at least part of a flash cache;
performing a comparison between the expected number of allocated cache pages and an actual number of allocated or free cache pages in connection with the non-volatile storage device; and
based on the comparison, selecting a free cache page in connection with the non-volatile storage device to allocate as a cache page, to balance the allocated or free cache pages among a plurality of non-volatile storage devices that form the flash cache, wherein the non-volatile storage device is one of the plurality of non-volatile storage devices that forms the flash cache; and wherein determining the expected number of allocated cache pages in connection with the non-volatile storage device comprises: forming a first value relating to available cache storage associated with the non-volatile storage device; forming a second value relating to available cache storage associated with the flash cache; forming a ratio of the first value to the second value to produce a third value; forming a fourth value relating to an actual number of allocated cache pages in connection with the flash cache; and forming a product of the third and fourth values to produce the expected number of allocated cache pages in connection with the non-volatile storage device.
14. The computer program product as claimed in claim 13 , wherein the non-volatile storage device is one of the plurality of non-volatile storage devices that forms the flash cache; and
wherein the method further comprises:
receiving a write I/O relating to a cache page in connection with another non-volatile storage device of the plurality of non-volatile storage devices that forms the flash cache;
performing a second comparison between the expected number of allocated cache pages and an actual number of allocated or free cache pages in connection with the another non-volatile storage device;
based on the second comparison, writing data associated with the write I/O to the selected cache page in connection with the non-volatile storage device; and
sending a command to free the cache page in connection with the another non-volatile storage device.
15. The computer program product as claimed in claim 13 , wherein the non-volatile storage device is one of the plurality of non-volatile storage devices that forms the flash cache; and
wherein the method further comprises:
receiving data that is one of promoted or demoted to the flash cache; and
storing the data in the selected cache page in connection with the non-volatile storage device of the plurality of non-volatile storage devices that forms the flash cache.
16. The computer program product as claimed in claim 13 , wherein the non-volatile storage device is one of the plurality of non-volatile storage devices that forms the flash cache; and
wherein the method further comprises:
detecting an intention to remove one of the plurality of non-volatile storage devices from the flash cache; and
moving data associated with a cache page in connection with the one of the plurality of non-volatile storage devices to the selected cache page.
17. The computer program product as claimed in claim 13 , wherein the actual number corresponds to the amount of allocated cache pages in connection with the non-volatile storage device; and
wherein performing the comparison, comprises:
determining if the expected number of allocated cache pages is greater or less than the actual number of allocated cache pages in connection with the non-volatile storage device; and
in response to determining the expected number is greater than the actual number, determining to select a free cache page in connection with the non-volatile storage device to allocate as a cache page.