Direct parameter

The direct parameter controls whether the page cache is used for fio I/O operations.

The page cache is an area of memory maintained by the Linux® kernel for the purpose of caching data resulting from user process I/O operations. If the page cache is used, then Linux intermediately caches that data in the page cache. The page cache is flushed at a later point in time, based on internal decisions by the Linux system. The use of the page cache implies a higher memory usage, in the sense of that much more memory pages per second are dirtied. If direct I/O is used, then the data transfer by the fio user process goes directly from the application buffers to the data files, avoiding operating system caching.