µC/FS is configurable at compile time via approximately 30 #defines in an application’s fs_cfg.h file. µC/FS uses #defines because they allow code and data sizes to be scaled at compile time based on enabled features. In other words, this allows the ROM and RAM footprints of µC/FS to be adjusted based on your requirements.
Most of the #defines should be configured with the default configuration values. This leaves about a dozen or so values that should be configured with values that may deviate from the default configuration.