Retrieves information about memory usage by file cache.
This function has no parameters.
Array of meta data about file cache memory usage or false on failure
The array returned by this function contains the following elements:
memory_total - amount of memory in bytes allocated for the file cache
memory_free - amount of free memory in bytes available for the file cache
num_used_blks - number of memory blocks used by the file cache
num_free_blks - number of free memory blocks available for the file cache
memory_overhead - amount of memory in bytes used for the file cache internal structures