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SubjectRe: [PATCH 16/17] writeback: trace event writeback_single_inode
On Fri, May 13, 2011 at 01:37:00PM +0800, Wu Fengguang wrote:
> On Fri, May 13, 2011 at 07:20:51AM +0800, Dave Chinner wrote:
> > On Thu, May 12, 2011 at 09:57:22PM +0800, Wu Fengguang wrote:
> > > 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 to_write=1024 wrote=0"
> > >
> > > - "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 2011-05-12 11:46:27.000000000 +0800
> > > +++ linux-next/include/trace/events/writeback.h 2011-05-12 11:48:55.000000000 +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,
> > > @@ -201,6 +214,49 @@ 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 2011-05-12 11:46:27.000000000 +0800
> > > +++ linux-next/fs/fs-writeback.c 2011-05-12 11:48:55.000000000 +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;
> > > }
> >
> > I think I'd prefer two separate trace calls rather than jumping to
> > one. That is, a trace_writeback_single_inode_requeue() event and a
> > trace_writeback_single_inode_done() event so we can see the separate
> > conditions in the trace....
>
> The requeue events are likely to disappear when IO-less
> balance_dirty_pages() are upstream. Do you still feel like adding a
> trace for it?

Requeue events are not specific to balance_dirty_pages() based
writeback. background/kupdate writeback can trigger them because a
sync write, fsync or sync is in progress. So yes, please add a
separate trace for it.

Cheers,

Dave.
--
Dave Chinner
david@fromorbit.com


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