Memory system executing garbage collection
According to one embodiment, a memory system includes a nonvolatile memory, detection unit, management unit, selection unit, and garbage collection unit. The nonvolatile memory includes memory areas divided into units of execution of garbage collection. The detection unit detects a data amount of data written to a different memory area among the memory areas when the garbage collection is executed, for each of the memory areas. The management unit manages a threshold set for each of the memory areas. The selection unit selects, based on the data amount and the threshold for each of the memory areas, a memory area whose data amount is smaller than the threshold of the memory area. The garbage collection unit executes the garbage collection on the memory area selected by the selection unit.
1. A memory system comprising:
a nonvolatile memory including first and second memory areas; and
a controller controlling the nonvolatile memory, the controller configured to:
detect data amounts of valid data written to the first memory area and data amounts of valid data written to the second memory area;
update, if writing for the second memory area is executed after writing for the first memory area, at least one of first and second thresholds such that the first threshold corresponding to the first memory area is greater than the second threshold corresponding to the second memory area;
select the first memory area as a memory area of a garbage collection target if the data amounts of the first memory area are smaller than the first threshold, and select the second memory area as the memory area of the garbage collection target if the data amounts of the second memory area are smaller than the second threshold; and
execute garbage collection on the selected memory area of the garbage collection target.
2. The memory system of claim 1 , wherein
the first and second memory areas are two areas of memory areas included in the nonvolatile memory,
the first and second thresholds are two values of thresholds associated with the memory areas respectively,
the controller is further configured to manage order information including each of write orders for each of the memory areas, the write orders designating writing occurrence orders in which writing has occurred, and
the updating by the controller includes setting, based on the order information, at least one of the first and second thresholds such that the first threshold is greater than the second threshold.
3. The memory system of claim 2 , wherein the selecting by the controller includes calculating each of values obtained by subtracting each of data amounts for each of the memory areas from each of the thresholds for each of the memory areas, and selecting the memory area whose value is the greatest.
4. The memory system of claim 2 , wherein the selecting by the controller includes calculating each of values obtained by subtracting each of data amounts for each of the memory areas from each of the thresholds for each of the memory areas, and selecting the memory area whose value is not less than a set value that allows execution of the garbage collection.
5. The memory system of claim 2 , wherein the order information is information obtained by allocating ascending numbers designating each of the write orders for each of the memory areas.
6. The memory system of claim 5 , wherein the updating by the controller includes identifying that the writing for the first memory area is earlier than the writing for the second memory area, based on that a difference between a newest number and a first number corresponding to the first memory area is greater than a difference between the newest number and a second number corresponding to the second memory area.
7. A memory system comprising:
a nonvolatile memory including a first memory area for which a first threshold is set and a second memory area for which a second threshold is set; and
a controller controlling the nonvolatile memory, the controller configured to:
update, if data is written to the second memory area after data is written to the first memory area, at least one of first and second thresholds such that the first threshold is greater than the second threshold; and
execute garbage collection on the first memory area if valid data amounts detected in the first memory area are smaller than the first threshold, and execute the garbage collection on the second memory area if valid data amounts detected in the second memory area are smaller than the second threshold.