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>

3 files changed, 132 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);
         }
 
         /*
diff --git a/include/trace/events/writeback.h b/include/trace/events/writeback.h
index b453d92c2253..6a16fd2e70ed 100644
--- a/include/trace/events/writeback.h
+++ b/include/trace/events/writeback.h
@@ -32,6 +32,115 @@
 
 struct wb_writeback_work;
 
+TRACE_EVENT(writeback_dirty_page,
+
+        TP_PROTO(struct page *page, struct address_space *mapping),
+
+        TP_ARGS(page, mapping),
+
+        TP_STRUCT__entry (
+                __array(char, name, 32)
+                __field(unsigned long, ino)
+                __field(pgoff_t, index)
+        ),
+
+        TP_fast_assign(
+                strncpy(__entry->name,
+                        mapping ? dev_name(mapping->backing_dev_info->dev) : "(unknown)", 32);
+                __entry->ino = mapping ? mapping->host->i_ino : 0;
+                __entry->index = page->index;
+        ),
+
+        TP_printk("bdi %s: ino=%lu index=%lu",
+                __entry->name,
+                __entry->ino,
+                __entry->index
+        )
+);
+
+DECLARE_EVENT_CLASS(writeback_dirty_inode_template,
+
+        TP_PROTO(struct inode *inode, int flags),
+
+        TP_ARGS(inode, flags),
+
+        TP_STRUCT__entry (
+                __array(char, name, 32)
+                __field(unsigned long, ino)
+                __field(unsigned long, flags)
+        ),
+
+        TP_fast_assign(
+                struct backing_dev_info *bdi = inode->i_mapping->backing_dev_info;
+
+                /* may be called for files on pseudo FSes w/ unregistered bdi */
+                strncpy(__entry->name,
+                        bdi->dev ? dev_name(bdi->dev) : "(unknown)", 32);
+                __entry->ino            = inode->i_ino;
+                __entry->flags          = flags;
+        ),
+
+        TP_printk("bdi %s: ino=%lu flags=%s",
+                __entry->name,
+                __entry->ino,
+                show_inode_state(__entry->flags)
+        )
+);
+
+DEFINE_EVENT(writeback_dirty_inode_template, writeback_dirty_inode_start,
+
+        TP_PROTO(struct inode *inode, int flags),
+
+        TP_ARGS(inode, flags)
+);
+
+DEFINE_EVENT(writeback_dirty_inode_template, writeback_dirty_inode,
+
+        TP_PROTO(struct inode *inode, int flags),
+
+        TP_ARGS(inode, flags)
+);
+
+DECLARE_EVENT_CLASS(writeback_write_inode_template,
+
+        TP_PROTO(struct inode *inode, struct writeback_control *wbc),
+
+        TP_ARGS(inode, wbc),
+
+        TP_STRUCT__entry (
+                __array(char, name, 32)
+                __field(unsigned long, ino)
+                __field(int, sync_mode)
+        ),
+
+        TP_fast_assign(
+                strncpy(__entry->name,
+                        dev_name(inode->i_mapping->backing_dev_info->dev), 32);
+                __entry->ino            = inode->i_ino;
+                __entry->sync_mode      = wbc->sync_mode;
+        ),
+
+        TP_printk("bdi %s: ino=%lu sync_mode=%d",
+                __entry->name,
+                __entry->ino,
+                __entry->sync_mode
+        )
+);
+
+DEFINE_EVENT(writeback_write_inode_template, writeback_write_inode_start,
+
+        TP_PROTO(struct inode *inode, struct writeback_control *wbc),
+
+        TP_ARGS(inode, wbc)
+);
+
+DEFINE_EVENT(writeback_write_inode_template, writeback_write_inode,
+
+        TP_PROTO(struct inode *inode, struct writeback_control *wbc),
+
+        TP_ARGS(inode, wbc)
+);
+
 DECLARE_EVENT_CLASS(writeback_work_class,
         TP_PROTO(struct backing_dev_info *bdi, struct wb_writeback_work *work),
         TP_ARGS(bdi, work),
@@ -479,6 +588,13 @@ DECLARE_EVENT_CLASS(writeback_single_inode_template,
         )
 );
 
+DEFINE_EVENT(writeback_single_inode_template, writeback_single_inode_start,
+        TP_PROTO(struct inode *inode,
+                 struct writeback_control *wbc,
+                 unsigned long nr_to_write),
+        TP_ARGS(inode, wbc, nr_to_write)
+);
+
 DEFINE_EVENT(writeback_single_inode_template, writeback_single_inode,
         TP_PROTO(struct inode *inode,
                  struct writeback_control *wbc,
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 0713bfbf0954..3734cefd4de4 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -1982,6 +1982,8 @@ int __set_page_dirty_no_writeback(struct page *page)
  */
 void account_page_dirtied(struct page *page, struct address_space *mapping)
 {
+        trace_writeback_dirty_page(page, mapping);
+
         if (mapping_cap_account_dirty(mapping)) {
                 __inc_zone_page_state(page, NR_FILE_DIRTY);
                 __inc_zone_page_state(page, NR_DIRTIED);