Memory system and method of controlling nonvolatile memory

A memory system, comprising:

• a nonvolatile memory;
• and
• a memory controller,
• wherein the nonvolatile memory includes a plurality of first storage regions,
• each of the first storage regions includes a plurality of second storage regions,
• each of the second storage regions is a unit of data writing and a unit of data reading,
• each of pieces of first data includes pieces of second data as storage target data,
• third data includes the pieces of the second data that are selected one by one from each of the pieces of the first data,
• the pieces of the second data that are included in the third data do not overlap the pieces of the second data that are included in another piece of third data, and
• the memory controller configured to,
• execute first decoding of decoding each of the pieces of the first data on the basis of a first error correcting code generated by using the first data,
• calculate first reliability of each bit in each of the second storage regions that fail in the first decoding, the first reliability being calculated by using a read value that is read from the nonvolatile memory by executing a soft-decision read, and
• execute second decoding of decoding the third data that includes one or more low reliability bits on the basis of a second error correcting code that is generated by using the third data, each of the low reliability bits being a bit of which the first reliability is less than second reliability of other bits of the third data.