Information processing device including nonvolatile cache memory and processor

1. An information processing device comprising:

a nonvolatile cache memory comprising a first group including a plurality of first erase unit areas, a second group including a plurality of second erase unit areas and a third group including a plurality of third erase unit areas, each of the first to third erase unit areas including a plurality of write unit areas, and data of each of the first to third erase unit areas being collectively erased per erase unit area by executing erase processing on each of the first to third erase unit areas; and

a processor configured to control the nonvolatile cache memory, communicate with an external memory system, and execute cache control for the nonvolatile cache memory having access speed higher than access speed of a nonvolatile memory device included in the external memory system, wherein the processor, in the cache control, is configured to:

write data into the first group;

generate management information including states of uses of data written in the first to third groups;

generate deletion information indicating whether or not the data written in the first to third groups are deletion target data, the deletion target data being a candidate of data to be deleted which is indicated by a program executed by the processor;

determine whether the first group satisfies a first erase condition or not;

select a first area to be erased from the first group if the first group satisfies the first erase condition;

determine, on the basis of the management information and the deletion information, whether first data written in the first area is in a first use state and whether the first data is the deletion target data;

write the first data into the second group if the first data is determined to be in the first use state and not to be the deletion target data;

write the first data into the third group if the first data is determined not to be in the first use state and not to be the deletion target data;

execute the erase processing on the first area in which the first data is written;

determine whether the second group satisfies a second erase condition or not;

select a second area to be erased from the second group if the second group satisfies the second erase condition;

determine, on the basis of the management information and the deletion information, whether second data written in the second area is in a second use state and whether the second data is the deletion target data;

write the second data into the third group if the second data is determined not to be in the second use state and not to be the deletion target data; and

execute the erase processing on the second area in which the second data is written.

2. The information processing device according to claim 1 , wherein

the nonvolatile cache memory further comprises a fourth group including a plurality of fourth erase unit areas, and

the processor, in the cache control, is further configured to

determine whether the third group satisfies a third erase condition or not;

select a third area to be erased from the third group if the third group satisfies the third erase condition;

determine, on the basis of the management information and the deletion information, whether third data written in the third area is in a third use state and whether the third data is the deletion target data;

write the third data written in the third area into the fourth group if the third data written in the third area is determined to be in the third use state and not to be the deletion target data;

write the third data written in the third area into the third group again if the third data written in the third area is determined not to be in the third use state and not to be the deletion target data; and

execute the erase processing on the third area in which the third data is written.

3. The information processing device according to claim 1 , wherein

the processor determines that the first erase condition is satisfied if a data amount of the first group exceeds a predetermined amount.

4. The information processing device according to claim 1 , wherein

the processor selects the first area to be erased from the first group on the basis of first-in first-out.

5. The information processing device according to claim 2 , wherein the processor is further configured to:

increase the number of the first erase unit areas included in the first group and reduce the number of the third erase unit areas included in the third group if data written in the second group reaches a fourth use state; and

increase the number of the third erase unit areas included in the third group and reduce the number of the first erase unit areas included in the first group if data written in the fourth group reaches a fifth use state.

6. The information processing device according to claim 5 , wherein the processor, in the cache control, is further configured to:

write fourth data written in the second group into the third group if the fourth data written in the second group and being not the deletion target data reaches the fourth use state.

7. The information processing device according to claim 2 , wherein the processor, in the cache control, is further configured to:

determine whether the second group satisfies a fourth erase condition or not;

select a fourth area to be erased from the second group if the second group satisfies the fourth erase condition;

execute the erase processing on the fourth area;

determine whether the fourth group satisfies a fifth erase condition or not;

select a fifth area to be erased from the fourth group if the fourth group satisfies the fifth erase condition; and

execute the erase processing on the fifth area.

8. The information processing device according to claim 7 , wherein

the processor selects, on the basis of first write times or first write orders of the plurality of second erase unit areas, an erase unit area indicating that the first write time or the first write order is old, as the fourth area to be erased, from the second group, and

selects, on the basis of second write times or second write orders of the plurality of fourth erase unit areas, an erase unit area indicating that the second write time or the second write order is old, as the fifth area to be erased, from the fourth group.

9. The information processing device according to claim 1 , wherein

the processor manages data used by the processor and logical and physical addresses indicative of the data used by the processor by a write through method or a write back method between the nonvolatile cache memory and the nonvolatile memory device.

10. The information processing device according to claim 1 , wherein

the first use state includes a state in which the first data is accessed a number of times less than a first number of times or at a frequency less than a first frequency.

11. The information processing device according to claim 2 , wherein

the third use state includes a state in which the third data is accessed a number of times less than a second number of times or at a frequency less than a second frequency.

12. The information processing device according to claim 5 , wherein

the fourth use state includes a state in which the data written in the second group is accessed by the processor, and

the fifth use state includes a state in which the data written in the fourth group is accessed by the processor.

13. The information processing device according to claim 1 , wherein

the processor is further configured to transmit the deletion information including a logical address indicative of the deletion target data, to the external memory system.

14. The information processing device according to claim 1 , wherein

the processor is further configured to receive data from the external memory system, and write the data received from the external memory system, to the nonvolatile cache memory.

15. The information processing device according to claim 14 , wherein

the processor is further configured to:

generate deletion information to be transmitted, the deletion information to be transmitted including a logical address indicative of the data which is the deletion target data and not stored in the nonvolatile cache memory; and

transmit the deletion information to be transmitted, to the external memory system.

16. The information processing device according to claim 1 , wherein

the nonvolatile cache memory is a NAND flash memory,

the first to third erase unit areas are blocks, and

the write unit areas are pages.