1. An information processing device including a memory management device, comprising: a processor; a volatile memory; a non-volatile memory; an accepter which accepts write-target-data from the processor; a storage which holds a coloring level; and an operating system which generates an access frequency of the write-target-data and an importance of the write-target-data, wherein the operating system: calculates the coloring level based on the access frequency of the write-target-data and the importance of the write-target-data, obtains a threshold value for selecting the volatile memory or the non-volatile memory, wherein the threshold value is determined based on a remaining capacity of a usable area in the volatile memory and the non-volatile memory, and determines whether to write the write-target-data in the volatile memory or the non-volatile memory by comparing the coloring level and the threshold value.