According to one embodiment, a memory system includes non-volatile memory, a block management table that stores whether data in the non-volatile memory is valid or invalid in a unit of cluster, and a controller configured to execute compaction. In the block management table, first information related to likelihood that valid data within the block is invalidated is registered for each of the blocks. The controller is configured to select a block to be a target of the compaction based on the first information and use the selected block to execute the compaction.