According to one embodiment, a memory system is connectable to a host. The memory system includes a nonvolatile memory and a controller. The nonvolatile memory includes a plurality of blocks. The controller is electrically coupled to the nonvolatile memory. The controller controls the nonvolatile memory. When receiving, from the host, a first command for changing a state of an allocated block to a reallocatable state in a case where a second command that is yet to be executed or being executed involving read of data from the allocated block has been received from the host, the controller changes the state of the allocated block to the reallocatable state after the second command is finished.