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    Subject[PATCH 16/17] writeback: trace event writeback_single_inode (v2)
    [changes:
    - move trace point into writeback_single_inode() to cover the other 2 callers;
    - change format to show the original rather than remained wbc->nr_to_write
    ]

    It is valuable to know how the dirty inodes are iterated and their IO size.

    "writeback_single_inode: bdi 8:0: ino=134246746 state=I_DIRTY_SYNC|I_SYNC age=414 index=0 wrote=0 to_write=1024"

    - "state" reflects inode->i_state at the end of writeback_single_inode()
    - "index" reflects mapping->writeback_index after the ->writepages() call
    - "to_write" is the wbc->nr_to_write at entrance of writeback_single_inode()
    - "wrote" is the number of pages actually written

    Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
    ---
    fs/fs-writeback.c | 6 ++-
    include/trace/events/writeback.h | 56 +++++++++++++++++++++++++++++
    2 files changed, 61 insertions(+), 1 deletion(-)

    --- linux-next.orig/include/trace/events/writeback.h 2011-05-06 12:10:16.000000000 +0800
    +++ linux-next/include/trace/events/writeback.h 2011-05-06 12:13:04.000000000 +0800
    @@ -8,6 +8,19 @@
    #include <linux/device.h>
    #include <linux/writeback.h>

    +#define show_inode_state(state) \
    + __print_flags(state, "|", \
    + {I_DIRTY_SYNC, "I_DIRTY_SYNC"}, \
    + {I_DIRTY_DATASYNC, "I_DIRTY_DATASYNC"}, \
    + {I_DIRTY_PAGES, "I_DIRTY_PAGES"}, \
    + {I_NEW, "I_NEW"}, \
    + {I_WILL_FREE, "I_WILL_FREE"}, \
    + {I_FREEING, "I_FREEING"}, \
    + {I_CLEAR, "I_CLEAR"}, \
    + {I_SYNC, "I_SYNC"}, \
    + {I_REFERENCED, "I_REFERENCED"} \
    + )
    +
    struct wb_writeback_work;

    DECLARE_EVENT_CLASS(writeback_work_class,
    @@ -180,6 +193,49 @@ DEFINE_EVENT(writeback_congest_waited_te
    TP_ARGS(usec_timeout, usec_delayed)
    );

    +TRACE_EVENT(writeback_single_inode,
    +
    + TP_PROTO(struct inode *inode,
    + struct writeback_control *wbc,
    + unsigned long nr_to_write
    + ),
    +
    + TP_ARGS(inode, wbc, nr_to_write),
    +
    + TP_STRUCT__entry(
    + __array(char, name, 32)
    + __field(unsigned long, ino)
    + __field(unsigned long, state)
    + __field(unsigned long, age)
    + __field(unsigned long, writeback_index)
    + __field(long, nr_to_write)
    + __field(unsigned long, wrote)
    + ),
    +
    + TP_fast_assign(
    + strncpy(__entry->name,
    + dev_name(inode->i_mapping->backing_dev_info->dev), 32);
    + __entry->ino = inode->i_ino;
    + __entry->state = inode->i_state;
    + __entry->age = (jiffies - inode->dirtied_when) *
    + 1000 / HZ;
    + __entry->writeback_index = inode->i_mapping->writeback_index;
    + __entry->nr_to_write = nr_to_write;
    + __entry->wrote = nr_to_write - wbc->nr_to_write;
    + ),
    +
    + TP_printk("bdi %s: ino=%lu state=%s age=%lu "
    + "index=%lu to_write=%ld wrote=%lu",
    + __entry->name,
    + __entry->ino,
    + show_inode_state(__entry->state),
    + __entry->age,
    + __entry->writeback_index,
    + __entry->nr_to_write,
    + __entry->wrote
    + )
    +);
    +
    #endif /* _TRACE_WRITEBACK_H */

    /* This part must be outside protection */
    --- linux-next.orig/fs/fs-writeback.c 2011-05-06 12:10:16.000000000 +0800
    +++ linux-next/fs/fs-writeback.c 2011-05-06 12:11:48.000000000 +0800
    @@ -356,6 +356,7 @@ writeback_single_inode(struct inode *ino
    struct writeback_control *wbc)
    {
    struct address_space *mapping = inode->i_mapping;
    + long nr_to_write = wbc->nr_to_write;
    unsigned dirty;
    int ret;

    @@ -378,7 +379,8 @@ writeback_single_inode(struct inode *ino
    */
    if (wbc->sync_mode != WB_SYNC_ALL) {
    requeue_io(inode, wb);
    - return 0;
    + ret = 0;
    + goto out;
    }

    /*
    @@ -476,6 +478,8 @@ writeback_single_inode(struct inode *ino
    }
    }
    inode_sync_complete(inode);
    +out:
    + trace_writeback_single_inode(inode, wbc, nr_to_write);
    return ret;
    }


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