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    SubjectRe: [PATCH 22/35] writeback: trace global dirty page states
    On Fri, Dec 17, 2010 at 10:19:34AM +0800, Wu Fengguang wrote:
    > On Mon, Dec 13, 2010 at 10:47:08PM +0800, Wu, Fengguang wrote:
    >
    > > + TP_fast_assign(
    > > + strlcpy(__entry->bdi,
    > > + dev_name(mapping->backing_dev_info->dev), 32);
    > > + __entry->ino = mapping->host->i_ino;
    >
    > I got an oops against the above line on shmem. Can be fixed by the
    > below patch, but still not 100% confident..

    btw, here is a cleanup of the tracepoint.

    Thanks,
    Fengguang
    ---
    Subject: writeback: simplify and rename tracepoint balance_dirty_state to global_dirty_state
    Date: Fri Dec 17 10:37:35 CST 2010

    Make it a more clean interface, and also track the background flusher
    when it calls over_bground_thresh() to check the global limits.

    The removed information could go into tracepoint balance_dirty_pages.

    Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
    ---
    include/trace/events/writeback.h | 37 +++++++----------------------
    mm/page-writeback.c | 16 +++---------
    2 files changed, 13 insertions(+), 40 deletions(-)

    --- linux-next.orig/include/trace/events/writeback.h 2010-12-17 11:05:08.000000000 +0800
    +++ linux-next/include/trace/events/writeback.h 2010-12-17 11:06:20.000000000 +0800
    @@ -149,60 +149,41 @@ DEFINE_WBC_EVENT(wbc_writeback_written);
    DEFINE_WBC_EVENT(wbc_writeback_wait);
    DEFINE_WBC_EVENT(wbc_writepage);

    -TRACE_EVENT(balance_dirty_state,
    +TRACE_EVENT(global_dirty_state,

    - TP_PROTO(struct address_space *mapping,
    - unsigned long nr_dirty,
    - unsigned long nr_writeback,
    - unsigned long nr_unstable,
    - unsigned long background_thresh,
    + TP_PROTO(unsigned long background_thresh,
    unsigned long dirty_thresh
    ),

    - TP_ARGS(mapping,
    - nr_dirty,
    - nr_writeback,
    - nr_unstable,
    - background_thresh,
    + TP_ARGS(background_thresh,
    dirty_thresh
    ),

    TP_STRUCT__entry(
    - __array(char, bdi, 32)
    - __field(unsigned long, ino)
    __field(unsigned long, nr_dirty)
    __field(unsigned long, nr_writeback)
    __field(unsigned long, nr_unstable)
    __field(unsigned long, background_thresh)
    __field(unsigned long, dirty_thresh)
    - __field(unsigned long, task_dirtied_pause)
    ),

    TP_fast_assign(
    - strlcpy(__entry->bdi,
    - dev_name(mapping->backing_dev_info->dev), 32);
    - __entry->ino = mapping->host->i_ino;
    - __entry->nr_dirty = nr_dirty;
    - __entry->nr_writeback = nr_writeback;
    - __entry->nr_unstable = nr_unstable;
    + __entry->nr_dirty = global_page_state(NR_FILE_DIRTY);
    + __entry->nr_writeback = global_page_state(NR_WRITEBACK);
    + __entry->nr_unstable = global_page_state(NR_UNSTABLE_NFS);
    __entry->background_thresh = background_thresh;
    __entry->dirty_thresh = dirty_thresh;
    - __entry->task_dirtied_pause = current->nr_dirtied_pause;
    ),

    - TP_printk("bdi %s: dirty=%lu wb=%lu unstable=%lu "
    - "bg_thresh=%lu thresh=%lu gap=%ld "
    - "poll_thresh=%lu ino=%lu",
    - __entry->bdi,
    + TP_printk("dirty=%lu writeback=%lu unstable=%lu "
    + "bg_thresh=%lu thresh=%lu gap=%ld",
    __entry->nr_dirty,
    __entry->nr_writeback,
    __entry->nr_unstable,
    __entry->background_thresh,
    __entry->dirty_thresh,
    __entry->dirty_thresh - __entry->nr_dirty -
    - __entry->nr_writeback - __entry->nr_unstable,
    - __entry->task_dirtied_pause,
    - __entry->ino
    + __entry->nr_writeback - __entry->nr_unstable
    )
    );

    --- linux-next.orig/mm/page-writeback.c 2010-12-17 11:05:08.000000000 +0800
    +++ linux-next/mm/page-writeback.c 2010-12-17 11:05:09.000000000 +0800
    @@ -418,6 +418,7 @@ void global_dirty_limits(unsigned long *
    }
    *pbackground = background;
    *pdirty = dirty;
    + trace_global_dirty_state(background, dirty);
    }

    /**
    @@ -712,21 +713,12 @@ static void balance_dirty_pages(struct a
    * written to the server's write cache, but has not yet
    * been flushed to permanent storage.
    */
    - nr_reclaimable = global_page_state(NR_FILE_DIRTY);
    - bdi_dirty = global_page_state(NR_UNSTABLE_NFS);
    - nr_dirty = global_page_state(NR_WRITEBACK);
    + nr_reclaimable = global_page_state(NR_FILE_DIRTY) +
    + global_page_state(NR_UNSTABLE_NFS);
    + nr_dirty = nr_reclaimable + global_page_state(NR_WRITEBACK);

    global_dirty_limits(&background_thresh, &dirty_thresh);

    - trace_balance_dirty_state(mapping,
    - nr_reclaimable,
    - nr_dirty,
    - bdi_dirty,
    - background_thresh,
    - dirty_thresh);
    - nr_reclaimable += bdi_dirty;
    - nr_dirty += nr_reclaimable;
    -
    /*
    * Throttle it only when the background writeback cannot
    * catch-up. This avoids (excessively) small writeouts

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