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    Subject[PATCH 16/18] writeback: trace event writeback_queue_io
    Note that it adds a little overheads to account the moved/enqueued
    inodes from b_dirty to b_io. The "moved" accounting may be later used to
    limit the number of inodes that can be moved in one shot, in order to
    keep spinlock hold time under control.

    Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
    ---
    fs/fs-writeback.c | 14 ++++++++++----
    include/trace/events/writeback.h | 25 +++++++++++++++++++++++++
    2 files changed, 35 insertions(+), 4 deletions(-)

    --- linux-next.orig/fs/fs-writeback.c 2011-05-24 11:17:26.000000000 +0800
    +++ linux-next/fs/fs-writeback.c 2011-05-24 11:17:27.000000000 +0800
    @@ -248,15 +248,16 @@ static bool inode_dirtied_after(struct i
    /*
    * Move expired dirty inodes from @delaying_queue to @dispatch_queue.
    */
    -static void move_expired_inodes(struct list_head *delaying_queue,
    +static int move_expired_inodes(struct list_head *delaying_queue,
    struct list_head *dispatch_queue,
    - unsigned long *older_than_this)
    + unsigned long *older_than_this)
    {
    LIST_HEAD(tmp);
    struct list_head *pos, *node;
    struct super_block *sb = NULL;
    struct inode *inode;
    int do_sb_sort = 0;
    + int moved = 0;

    while (!list_empty(delaying_queue)) {
    inode = wb_inode(delaying_queue->prev);
    @@ -267,12 +268,13 @@ static void move_expired_inodes(struct l
    do_sb_sort = 1;
    sb = inode->i_sb;
    list_move(&inode->i_wb_list, &tmp);
    + moved++;
    }

    /* just one sb in list, splice to dispatch_queue and we're done */
    if (!do_sb_sort) {
    list_splice(&tmp, dispatch_queue);
    - return;
    + goto out;
    }

    /* Move inodes from one superblock together */
    @@ -284,6 +286,8 @@ static void move_expired_inodes(struct l
    list_move(&inode->i_wb_list, dispatch_queue);
    }
    }
    +out:
    + return moved;
    }

    /*
    @@ -299,9 +303,11 @@ static void move_expired_inodes(struct l
    */
    static void queue_io(struct bdi_writeback *wb, unsigned long *older_than_this)
    {
    + int moved;
    assert_spin_locked(&wb->list_lock);
    list_splice_init(&wb->b_more_io, &wb->b_io);
    - move_expired_inodes(&wb->b_dirty, &wb->b_io, older_than_this);
    + moved = move_expired_inodes(&wb->b_dirty, &wb->b_io, older_than_this);
    + trace_writeback_queue_io(wb, older_than_this, moved);
    }

    static int write_inode(struct inode *inode, struct writeback_control *wbc)
    --- linux-next.orig/include/trace/events/writeback.h 2011-05-24 11:17:26.000000000 +0800
    +++ linux-next/include/trace/events/writeback.h 2011-05-24 11:17:27.000000000 +0800
    @@ -162,6 +162,31 @@ DEFINE_WBC_EVENT(wbc_balance_dirty_writt
    DEFINE_WBC_EVENT(wbc_balance_dirty_wait);
    DEFINE_WBC_EVENT(wbc_writepage);

    +TRACE_EVENT(writeback_queue_io,
    + TP_PROTO(struct bdi_writeback *wb,
    + unsigned long *older_than_this,
    + int moved),
    + TP_ARGS(wb, older_than_this, moved),
    + TP_STRUCT__entry(
    + __array(char, name, 32)
    + __field(unsigned long, older)
    + __field(long, age)
    + __field(int, moved)
    + ),
    + TP_fast_assign(
    + strncpy(__entry->name, dev_name(wb->bdi->dev), 32);
    + __entry->older = older_than_this ? *older_than_this : 0;
    + __entry->age = older_than_this ?
    + (jiffies - *older_than_this) * 1000 / HZ : -1;
    + __entry->moved = moved;
    + ),
    + TP_printk("bdi %s: older=%lu age=%ld enqueue=%d",
    + __entry->name,
    + __entry->older, /* older_than_this in jiffies */
    + __entry->age, /* older_than_this in relative milliseconds */
    + __entry->moved)
    +);
    +
    DECLARE_EVENT_CLASS(writeback_congest_waited_template,

    TP_PROTO(unsigned int usec_timeout, unsigned int usec_delayed),



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