writeback: add more tracepoints

Add tracepoints for page dirtying, writeback_single_inode start, inode
dirtying and writeback.  For the latter two inode events, a pair of
events are defined to denote start and end of the operations (the
starting one has _start suffix and the one w/o suffix happens after
the operation is complete).  These inode ops are FS specific and can
be non-trivial and having enclosing tracepoints is useful for external
tracers.

This is part of tracepoint additions to improve visiblity into
dirtying / writeback operations for io tracer and userland.

v2: writeback_dirty_inode[_start] TPs may be called for files on
    pseudo FSes w/ unregistered bdi.  Check whether bdi->dev is %NULL
    before dereferencing.

v3: buffer dirtying moved to a block TP.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 14 insertions, 2 deletions

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 310972b72a66..359494ea1bde 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -318,8 +318,14 @@ static void queue_io(struct bdi_writeback *wb, struct wb_writeback_work *work)
 
 static int write_inode(struct inode *inode, struct writeback_control *wbc)
 {
-        if (inode->i_sb->s_op->write_inode && !is_bad_inode(inode))
-                return inode->i_sb->s_op->write_inode(inode, wbc);
+        int ret;
+
+        if (inode->i_sb->s_op->write_inode && !is_bad_inode(inode)) {
+                trace_writeback_write_inode_start(inode, wbc);
+                ret = inode->i_sb->s_op->write_inode(inode, wbc);
+                trace_writeback_write_inode(inode, wbc);
+                return ret;
+        }
         return 0;
 }
 
@@ -450,6 +456,8 @@ __writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
 
         WARN_ON(!(inode->i_state & I_SYNC));
 
+        trace_writeback_single_inode_start(inode, wbc, nr_to_write);
+
         ret = do_writepages(mapping, wbc);
 
         /*
@@ -1150,8 +1158,12 @@ void __mark_inode_dirty(struct inode *inode, int flags)
          * dirty the inode itself
          */
         if (flags & (I_DIRTY_SYNC | I_DIRTY_DATASYNC)) {
+                trace_writeback_dirty_inode_start(inode, flags);
+
                 if (sb->s_op->dirty_inode)
                         sb->s_op->dirty_inode(inode, flags);
+
+                trace_writeback_dirty_inode(inode, flags);
         }
 
         /*