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    Subject[PATCHv4 14/14] writeback: add new tracepoints
    Date
    From: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>

    Add 2 new trace points to the periodic write-back wake up case, just like we do
    in the 'bdi_queue_work()' function. Namely, introduce:

    1. trace_writeback_wakeup(bdi)
    2. trace_writeback_wakeup_nothread(bdi)

    The first event is triggered every time we wake up a bdi thread to start
    periodic background write-out. The second event is triggered only when the bdi
    thread does not exist and should be created by the forker thread.

    This patch was suggested by Dave Chinner <david@fromorbit.com>

    Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
    ---
    include/trace/events/writeback.h | 2 ++
    mm/backing-dev.c | 3 +++
    2 files changed, 5 insertions(+), 0 deletions(-)

    diff --git a/include/trace/events/writeback.h b/include/trace/events/writeback.h
    index 84ab72d..eb07d48 100644
    --- a/include/trace/events/writeback.h
    +++ b/include/trace/events/writeback.h
    @@ -81,6 +81,8 @@ DEFINE_EVENT(writeback_class, name, \
    TP_ARGS(bdi))

    DEFINE_WRITEBACK_EVENT(writeback_nowork);
    +DEFINE_WRITEBACK_EVENT(writeback_wakeup);
    +DEFINE_WRITEBACK_EVENT(writeback_wakeup_nothread);
    DEFINE_WRITEBACK_EVENT(writeback_bdi_register);
    DEFINE_WRITEBACK_EVENT(writeback_bdi_unregister);
    DEFINE_WRITEBACK_EVENT(writeback_thread_start);
    diff --git a/mm/backing-dev.c b/mm/backing-dev.c
    index ce105fc..22fc506 100644
    --- a/mm/backing-dev.c
    +++ b/mm/backing-dev.c
    @@ -308,6 +308,8 @@ static void wakeup_timer_fn(unsigned long data)
    {
    struct backing_dev_info *bdi = (struct backing_dev_info *)data;

    + trace_writeback_wakeup(bdi);
    +
    spin_lock(&bdi->wb_lock);
    if (bdi->wb.task) {
    wake_up_process(bdi->wb.task);
    @@ -317,6 +319,7 @@ static void wakeup_timer_fn(unsigned long data)
    * In this case we have to wake-up the forker thread which
    * should create and run the bdi thread.
    */
    + trace_writeback_wakeup_nothread(bdi);
    wake_up_process(default_backing_dev_info.wb.task);
    }
    spin_unlock(&bdi->wb_lock);
    --
    1.7.1.1


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