A memory system may include a memory device including a plurality of memory blocks and a controller suitable for determining whether to change from a normal mode to a dirty mode based on a size of free space of a host a sum of an amount of restoration of garbage collection for victim blocks and a size of all free blocks in the memory device. In the dirty mode, the controller controls the memory device to perform a garbage collection operation on the victim blocks at a frequency greater than frequency at which a garbage collection operation is performed in the normal mode.