1. A computer-implemented method, comprising: determining, by a computing device, whether a free space cache inode generation number stored in a free space cache inode of an on-disk free space cache of a block group is valid, wherein the on-disk free space cache is stored in persistent data storage indexed by a file system of the computing device; determining, by the computing device, whether a free space cache item generation number stored in a free space cache item of the free space cache is valid by comparing the free space cache item generation number to the free space cache inode generation number; determining, by the computing device, whether a free space cache header generation number stored in a free space cache header of the free space cache is valid by comparing the free space cache header generation number to the free space cache item generation number; determining, by the computing device, whether a checksum generated for a first page of the free space cache matches a checksum stored in the file system and associated with the free space cache; and adding, by the computing device, entries stored in the on-disk free space cache to an in-memory free space cache for the block group kept in volatile memory of the computing device.