From: "Kani, Toshimitsu" <toshi.kani@hpe.com>
To: "dan.j.williams@intel.com" <dan.j.williams@intel.com>
CC: "viro@zeniv.linux.org.uk" <viro@zeniv.linux.org.uk>,
        "ross.zwisler@linux.intel.com" <ross.zwisler@linux.intel.com>,
        "linux-nvdimm@lists.01.org" <linux-nvdimm@ml01.01.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "akpm@linux-foundation.org" <akpm@linux-foundation.org>,
        "linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>
Subject: Re: [PATCH] DAX: enable iostat for read/write
Thread-Topic: [PATCH] DAX: enable iostat for read/write
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Date: Fri, 14 Oct 2016 18:47:36 +0000
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On Fri, 2016-10-14 at 10:35 -0700, Dan Williams wrote:
> On Fri, Oct 14, 2016 at 10:25 AM, 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: Alexander Viro <viro@zeniv.linux.org.uk>
> > Cc: Dan Williams <dan.j.williams@intel.com>
> > Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
> > ---
> >  fs/dax.c |   37 +++++++++++++++++++++++++++++++++++++
> >  1 file changed, 37 insertions(+)
> > 
> > diff --git a/fs/dax.c b/fs/dax.c
> > index 014defd..3aaaac2 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;
> 
> Should this be a minimum of one sector since we allow unaligned
> transfers through this interface?
> 
> ...or is iov_iter_count() somehow guaranteed to be sector aligned
> here?

You are right. I will update to set a minimum of one sector in v2. 

Thanks!
-Toshi