f2fs: add a tracepoint for f2fs_read_data_pages

This patch adds a tracepoint for f2fs_read_data_pages to trace when pages
are readahead by VFS.
Signed-off-by: Chao Yu <chao2.yu@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/data.c

@@ -1032,6 +1032,9 @@ static int f2fs_read_data_pages(struct file *file,
 			struct list_head *pages, unsigned nr_pages)
 {
 	struct inode *inode = file->f_mapping->host;
+	struct page *page = list_entry(pages->prev, struct page, lru);
+
+	trace_f2fs_readpages(inode, page, nr_pages);
 
 	/* If the file has inline data, skip readpages */
 	if (f2fs_has_inline_data(inode))

include/trace/events/f2fs.h

@@ -1028,6 +1028,32 @@ TRACE_EVENT(f2fs_writepages,
 		__entry->for_sync)
 );
 
+TRACE_EVENT(f2fs_readpages,
+
+	TP_PROTO(struct inode *inode, struct page *page, unsigned int nrpage),
+
+	TP_ARGS(inode, page, nrpage),
+
+	TP_STRUCT__entry(
+		__field(dev_t,	dev)
+		__field(ino_t,	ino)
+		__field(pgoff_t,	start)
+		__field(unsigned int,	nrpage)
+	),
+
+	TP_fast_assign(
+		__entry->dev	= inode->i_sb->s_dev;
+		__entry->ino	= inode->i_ino;
+		__entry->start	= page->index;
+		__entry->nrpage	= nrpage;
+	),
+
+	TP_printk("dev = (%d,%d), ino = %lu, start = %lu nrpage = %u",
+		show_dev_ino(__entry),
+		(unsigned long)__entry->start,
+		__entry->nrpage)
+);
+
 TRACE_EVENT(f2fs_write_checkpoint,
 
 	TP_PROTO(struct super_block *sb, int reason, char *msg),