task_io_accounting.h

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/*
 * task_io_accounting: a structure which is used for recording a single task's
 * IO statistics.
 *
 * Don't include this header file directly - it is designed to be dragged in via
 * sched.h.
 *
 * Blame Andrew Morton for all this.
 */

struct task_io_accounting {
#ifdef CONFIG_TASK_XACCT
    /* bytes read */
    u64 rchar;
    /*  bytes written */
    u64 wchar;
    /* # of read syscalls */
    u64 syscr;
    /* # of write syscalls */
    u64 syscw;
#endif /* CONFIG_TASK_XACCT */

#ifdef CONFIG_TASK_IO_ACCOUNTING
    /*
     * The number of bytes which this task has caused to be read from
     * storage.
     */
    u64 read_bytes;

    /*
     * The number of bytes which this task has caused, or shall cause to be
     * written to disk.
     */
    u64 write_bytes;

    /*
     * A task can cause "negative" IO too.  If this task truncates some
     * dirty pagecache, some IO which another task has been accounted for
     * (in its write_bytes) will not be happening.  We _could_ just
     * subtract that from the truncating task's write_bytes, but there is
     * information loss in doing that.
     */
    u64 cancelled_write_bytes;
#endif /* CONFIG_TASK_IO_ACCOUNTING */
};