1. A memory system is connectable to a host, the memory system comprising: a first memory as a nonvolatile memory storing information regarding an address translation between a logical address and a physical address; a second memory temporarily storing a first part and a second part of the information; a controller circuitry configured to: execute a read operation and a write operation of the first part of the information from and to the second memory in a first unit, be able to change a size of the first unit, the size of the first unit being a size of one of regions obtained by dividing in a first logical address space of the memory system, the size of each of the regions being equal to each other in the first logical address space, execute a read operation and a write operation of the second part of the information from and to the second memory in a second unit, the second unit being different from the first unit, and be able to change a size of the second unit, the size of the second unit being a size of one of regions obtained by dividing a second logical address space of the memory system, the second logical address space being different from the first logical address space.