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    Subject[FSAIO][PATCH 4/8] Add a default io wait bit field in task struct

    Allocates space for the default io wait queue entry (actually a wait
    bit entry) in the task struct. Doing so simplifies the patches
    for AIO wait page allowing for cleaner and more efficient
    implementation, at the cost of 28 additional bytes in task struct
    vs allocation on demand on-stack.

    Signed-off-by: Suparna Bhattacharya <suparna@in.ibm.com>
    Acked-by: Ingo Molnar <mingo@elte.hu>
    ---

    linux-2.6.20-rc1-root/include/linux/sched.h | 11 +++++++----
    linux-2.6.20-rc1-root/kernel/fork.c | 3 ++-
    2 files changed, 9 insertions(+), 5 deletions(-)

    diff -puN include/linux/sched.h~tsk-default-io-wait include/linux/sched.h
    --- linux-2.6.20-rc1/include/linux/sched.h~tsk-default-io-wait 2006-12-21 08:45:51.000000000 +0530
    +++ linux-2.6.20-rc1-root/include/linux/sched.h 2006-12-28 09:32:39.000000000 +0530
    @@ -1006,11 +1006,14 @@ struct task_struct {

    unsigned long ptrace_message;
    siginfo_t *last_siginfo; /* For ptrace use. */
    +
    +/* Space for default IO wait bit entry used for synchronous IO waits */
    + struct wait_bit_queue __wait;
    /*
    - * current io wait handle: wait queue entry to use for io waits
    - * If this thread is processing aio, this points at the waitqueue
    - * inside the currently handled kiocb. It may be NULL (i.e. default
    - * to a stack based synchronous wait) if its doing sync IO.
    + * Current IO wait handle: wait queue entry to use for IO waits
    + * If this thread is processing AIO, this points at the waitqueue
    + * inside the currently handled kiocb. Otherwise, points to the
    + * default IO wait field (i.e &__wait.wait above).
    */
    wait_queue_t *io_wait;
    /* i/o counters(bytes read/written, #syscalls */
    diff -puN kernel/fork.c~tsk-default-io-wait kernel/fork.c
    --- linux-2.6.20-rc1/kernel/fork.c~tsk-default-io-wait 2006-12-21 08:45:51.000000000 +0530
    +++ linux-2.6.20-rc1-root/kernel/fork.c 2006-12-21 08:45:51.000000000 +0530
    @@ -1056,7 +1056,8 @@ static struct task_struct *copy_process(
    do_posix_clock_monotonic_gettime(&p->start_time);
    p->security = NULL;
    p->io_context = NULL;
    - p->io_wait = NULL;
    + init_wait_bit_task(&p->__wait, p);
    + p->io_wait = &p->__wait.wait;
    p->audit_context = NULL;
    cpuset_fork(p);
    #ifdef CONFIG_NUMA
    _
    --
    Suparna Bhattacharya (suparna@in.ibm.com)
    Linux Technology Center
    IBM Software Lab, India
    -
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