DEFAULT_JOURNAL_IOPRIO

/* * 这些是 CFQ（完全公平排队）实现的 I/O 优先级组。

RT 是实时类，它总是能获得优质服务。

BE 是尽力而为的调度类，是任何进程的默认类别。

IDLE 是空闲调度类，只有在没有其他人使用磁盘时才会被服务。

*/

/*
 * These are the io priority groups as implemented by CFQ. RT is the realtime
 * class, it always gets premium service. BE is the best-effort scheduling
 * class, the default for any process. IDLE is the idle scheduling class, it
 * is only served when no one else is using the disk.
 */
enum {
    IOPRIO_CLASS_NONE,
    IOPRIO_CLASS_RT,
    IOPRIO_CLASS_BE,
    IOPRIO_CLASS_IDLE,
};

#define IOPRIO_PRIO_VALUE(class, data)    (((class) << IOPRIO_CLASS_SHIFT) | data)
 

#define DEFAULT_JOURNAL_IOPRIO (IOPRIO_PRIO_VALUE(IOPRIO_CLASS_BE, 3))