[PATCH v6] DAX: enable iostat for read/write

[Toshi Kani]

DAX IO path does not support iostat, but its metadata IO path does.
Therefore, iostat shows metadata IO statistics only, which has been
confusing to users.

Add iostat support to the DAX read/write path.

Note, iostat still does not support the DAX mmap path as it allows
user applications to access directly.

Signed-off-by: Toshi Kani <toshi.kani@xxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Dave Chinner <david@xxxxxxxxxxxxx>
Cc: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
Cc: Joe Perches <joe@xxxxxxxxxxx>
---
v6:
 - Change min_t() to max_t(), and sector_t to size_t. (Joe Perches)
---
 fs/dax.c |   15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/fs/dax.c b/fs/dax.c
index 5c74f60..ac04f21 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -1058,12 +1058,24 @@ dax_iomap_rw(struct kiocb *iocb, struct iov_iter *iter,
 {
 	struct address_space *mapping = iocb->ki_filp->f_mapping;
 	struct inode *inode = mapping->host;
+	struct gendisk *disk = inode->i_sb->s_bdev->bd_disk;
 	loff_t pos = iocb->ki_pos, ret = 0, done = 0;
 	unsigned flags = 0;
+	unsigned long start = 0;
+	int do_acct = blk_queue_io_stat(disk->queue);
 
 	if (iov_iter_rw(iter) == WRITE)
 		flags |= IOMAP_WRITE;
 
+	if (do_acct) {
+		size_t sec = iov_iter_count(iter) >> 9;
+
+		start = jiffies;
+		generic_start_io_acct(iov_iter_rw(iter),
+				      max_t(unsigned long, 1, sec),
+				      &disk->part0);
+	}
+
 	while (iov_iter_count(iter)) {
 		ret = iomap_apply(inode, pos, iov_iter_count(iter), flags, ops,
 				iter, dax_iomap_actor);
@@ -1073,6 +1085,9 @@ dax_iomap_rw(struct kiocb *iocb, struct iov_iter *iter,
 		done += ret;
 	}
 
+	if (do_acct)
+		generic_end_io_acct(iov_iter_rw(iter), &disk->part0, start);
+
 	iocb->ki_pos += done;
 	return done ? done : ret;
 }