Re: [PATCH v4] DAX: enable iostat for read/write

[Dan Williams]

On Tue, Jan 10, 2017 at 4:11 PM, 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.
>
> 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>
> ---
> v4: Rebased to 4.10, applied the v3 change to new dax_iomap_rw().
> ---
>  fs/dax.c |   13 +++++++++++++
>  1 file changed, 13 insertions(+)
>
> diff --git a/fs/dax.c b/fs/dax.c
> index 5c74f60..4d5f4c0 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -1058,12 +1058,22 @@ 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;
>
>         if (iov_iter_rw(iter) == WRITE)
>                 flags |= IOMAP_WRITE;
>
> +       if (blk_queue_io_stat(disk->queue)) {
> +               int sec = iov_iter_count(iter) >> 9;
> +
> +               start = jiffies;
> +               generic_start_io_acct(iov_iter_rw(iter),
> +                                     (!sec) ? 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 +1083,9 @@ dax_iomap_rw(struct kiocb *iocb, struct iov_iter *iter,
>                 done += ret;
>         }
>
> +       if (start)
> +               generic_end_io_acct(iov_iter_rw(iter), &disk->part0, start);
> +

I think we can afford to add a separate flag that indicates whether we
called generic_start_io_acct(). Just in case 'start' is '0' after
'jiffies' rolls over.