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

[Andrew Morton]

On Fri, 13 Jan 2017 16:34:18 -0700 Toshi Kani <toshi.kani@xxxxxxx> wrote:

> 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.
> 
> ...
>
> --- 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);

(The poorly named) blk_queue_io_stat() actually returns a bool.  This
is well concealed because blk_queue_io_stat() is unnecessarily
implemented as a macro (why oh why).

--- a/fs/dax.c~dax-enable-iostat-for-read-write-fix
+++ a/fs/dax.c
@@ -1085,7 +1085,7 @@ dax_iomap_rw(struct kiocb *iocb, struct
 	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);
+	bool do_acct = blk_queue_io_stat(disk->queue);
 
 	if (iov_iter_rw(iter) == WRITE)
 		flags |= IOMAP_WRITE;
_