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

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

[Dan Williams]

On Tue, Jan 10, 2017 at 4:11 PM, Toshi Kani <toshi.kani@hpe.com> 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@hpe.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: Alexander Viro <viro@zeniv.linux.org.uk>
> Cc: Dave Chinner <david@fromorbit.com>
> Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
> ---
> 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.

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

[Kani, Toshimitsu]

On Tue, 2017-01-10 at 15:41 -0800, Dan Williams wrote:
> On Tue, Jan 10, 2017 at 4:11 PM, Toshi Kani <toshi.kani@hpe.com>
> wrote:
 :
> > 
> > +       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.

Good point. I will add a flag to account such a case.

Thanks,
-Toshi

[PATCH v4] 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@hpe.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
---
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);
+
 	iocb->ki_pos += done;
 	return done ? done : ret;
 }

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

[Joe Perches]

On Tue, 2017-01-10 at 17:11 -0700, Toshi Kani 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.
[]
> diff --git a/fs/dax.c b/fs/dax.c
[]
> @@ -1058,12 +1058,22 @@ dax_iomap_rw(struct kiocb *iocb, struct iov_iter *iter,
[]
> +	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);
> +	}

There is a signed/unsigned conversion of sec
It may be better to use something like:

		size_t sec  = iov_iter_count(iter) >> 9;
		[...]
		generic_start_io_acct(iov_iter_rw(iter),
				      min_t(unsigned long, 1, sec),
				      &disk->part0);
> 

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

[Kani, Toshimitsu]

On Tue, 2017-01-10 at 20:36 -0800, Joe Perches wrote:
> > 
On Tue, 2017-01-10 at 17:11 -0700, Toshi Kani 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.
> 
> []
> > diff --git a/fs/dax.c b/fs/dax.c
> 
> []
> > @@ -1058,12 +1058,22 @@ dax_iomap_rw(struct kiocb *iocb, struct
> > iov_iter *iter,
> 
> []
> > +	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);
> > +	}
> 
> There is a signed/unsigned conversion of sec
> It may be better to use something like:
> 
> 		size_t sec  = iov_iter_count(iter) >> 9;
> 		[...]
> 		generic_start_io_acct(iov_iter_rw(iter),
> 				      min_t(unsigned long, 1, sec),
> 				      &disk->part0);

Good catch. I will change as you suggested, and use 'sector_t' for
'sec'. 

Thanks,
-Toshi