[PATCH v2] DAX: enable iostat for read/write

[Toshi Kani <toshi.kani@hpe.com>]

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@hpe.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
---
v2:
- Set a minimum of one sector (Dan Williams)
---
 fs/dax.c |   37 +++++++++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)

diff --git a/fs/dax.c b/fs/dax.c
index 014defd..43e5e7a 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -144,6 +144,34 @@ static sector_t to_sector(const struct buffer_head *bh,
 	return sector;
 }
 
+static void dax_iostat_start(struct gendisk *disk, struct iov_iter *iter,
+			     unsigned long *start)
+{
+	int rw = iov_iter_rw(iter);
+	int sec = iov_iter_count(iter) >> 9;
+	int cpu = part_stat_lock();
+
+	*start = jiffies;
+	part_round_stats(cpu, &disk->part0);
+	part_stat_inc(cpu, &disk->part0, ios[rw]);
+	part_stat_add(cpu, &disk->part0, sectors[rw], ((!sec) ? 1 : sec));
+	part_inc_in_flight(&disk->part0, rw);
+	part_stat_unlock();
+}
+
+static void dax_iostat_end(struct gendisk *disk, struct iov_iter *iter,
+			   unsigned long start)
+{
+	unsigned long duration = jiffies - start;
+	int rw = iov_iter_rw(iter);
+	int cpu = part_stat_lock();
+
+	part_stat_add(cpu, &disk->part0, ticks[rw], duration);
+	part_round_stats(cpu, &disk->part0);
+	part_dec_in_flight(&disk->part0, rw);
+	part_stat_unlock();
+}
+
 static ssize_t dax_io(struct inode *inode, struct iov_iter *iter,
 		      loff_t start, loff_t end, get_block_t get_block,
 		      struct buffer_head *bh)
@@ -265,9 +293,12 @@ ssize_t dax_do_io(struct kiocb *iocb, struct inode *inode,
 	ssize_t retval = -EINVAL;
 	loff_t pos = iocb->ki_pos;
 	loff_t end = pos + iov_iter_count(iter);
+	struct gendisk *disk;
+	unsigned long start = 0;
 
 	memset(&bh, 0, sizeof(bh));
 	bh.b_bdev = inode->i_sb->s_bdev;
+	disk = bh.b_bdev->bd_disk;
 
 	if ((flags & DIO_LOCKING) && iov_iter_rw(iter) == READ)
 		inode_lock(inode);
@@ -276,8 +307,14 @@ ssize_t dax_do_io(struct kiocb *iocb, struct inode *inode,
 	if (!(flags & DIO_SKIP_DIO_COUNT))
 		inode_dio_begin(inode);
 
+	if (blk_queue_io_stat(disk->queue))
+		dax_iostat_start(disk, iter, &start);
+
 	retval = dax_io(inode, iter, pos, end, get_block, &bh);
 
+	if (start)
+		dax_iostat_end(disk, iter, start);
+
 	if ((flags & DIO_LOCKING) && iov_iter_rw(iter) == READ)
 		inode_unlock(inode);