Memory system and method

A method of controlling a first memory, the first memory being a non-volatile memory and including a memory cell array that includes a plurality of memory cells, the method comprising:

• in response to receiving a write request from a host,
• allocating an area unit to a buffer area of a second memory that is a volatile memory;
• storing a data unit in the area unit, the data unit being requested by the write request to be written to the first memory;
• and
• executing, on the data unit, a write operation including a data-in operation and a program operation, the data-in operation being an operation of transferring the data unit to the first memory, the program operation being an operation of writing the data unit transferred to the first memory by the data-in operation to the memory cell array, and
• at a first timing within a period from the allocation of the area unit to completion of the data-in operation on the data unit stored in the area unit,
• determining that a usage of the buffer area is in a first state in which the usage of the buffer area is smaller than a first threshold value;
• deallocating the area unit upon the completion of the data-in operation on the data unit, in response to determining that the usage of the buffer area is in the first state;
• determining that the usage of the buffer area is in a second state in which the usage of the buffer area is larger than a second threshold value, the second threshold value being larger than the first threshold value;
• and
• deallocating the area unit upon completion of the program operation on the data unit, in response to determining that the usage of the buffer area is in the second state.