writeback: trace event writeback_single_inode

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

v2: add trace event writeback_single_inode_requeue as proposed by Dave.

CC: Dave Chinner <david@fromorbit.com>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index f43c479feee9..5185fad48b62 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -346,6 +346,7 @@ writeback_single_inode(struct inode *inode, struct bdi_writeback *wb,
                        struct writeback_control *wbc)
 {
         struct address_space *mapping = inode->i_mapping;
+        long nr_to_write = wbc->nr_to_write;
         unsigned dirty;
         int ret;
 
@@ -368,6 +369,8 @@ writeback_single_inode(struct inode *inode, struct bdi_writeback *wb,
                  */
                 if (wbc->sync_mode != WB_SYNC_ALL) {
                         requeue_io(inode, wb);
+                        trace_writeback_single_inode_requeue(inode, wbc,
+                                                             nr_to_write);
                         return 0;
                 }
 
@@ -467,6 +470,7 @@ writeback_single_inode(struct inode *inode, struct bdi_writeback *wb,
                 }
         }
         inode_sync_complete(inode);
+        trace_writeback_single_inode(inode, wbc, nr_to_write);
         return ret;
 }