Re: [PATCH 0/6] Support DAX for device-mapper dm-linear devices

From: "Kani, Toshimitsu" <toshi.kani-ZPxbGqLxI0U@public.gmane.org>
To: "dan.j.williams-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org"
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Subject: Re: [PATCH 0/6] Support DAX for device-mapper dm-linear devices
Date: Tue, 21 Jun 2016 16:35:56 +0000	[thread overview]
Message-ID: <1466526342.3504.270.camel@hpe.com> (raw)
In-Reply-To: <CAPcyv4gFREc94ANuFD_Lyddx3iqRTN2UDebgeJe3LqPL8xrVzg-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>

On Tue, 2016-06-21 at 09:25 -0700, Dan Williams wrote:
> On Tue, Jun 21, 2016 at 8:44 AM, Kani, Toshimitsu <toshi.kani@hpe.com>
> wrote:
> > 
> > On Tue, 2016-06-21 at 09:41 -0400, Mike Snitzer wrote:
> > > 
> > > On Mon, Jun 20 2016 at  6:22pm -0400,
> > > Mike Snitzer <snitzer@redhat.com> wrote:
> > > > 
> > > > On Mon, Jun 20 2016 at  5:28pm -0400,
> > > > Kani, Toshimitsu <toshi.kani@hpe.com> wrote:
> >  :
> > > > Looks good, I folded it in and tested it to work.  Pushed to my 'wip'
> > > > branch.
> > > > 
> > > > No longer seeing any corruption in my test that was using partitions
> > > > to span pmem devices with a dm-linear device.
> > > > 
> > > > Jens, any chance you'd be open to picking up the first 2 patches in
> > > > this series?  Or would you like to see them folded or something
> > > > different?
> > >
> > > I'm now wondering if we'd be better off setting a new QUEUE_FLAG_DAX
> > > rather than establish GENHD_FL_DAX on the genhd?
> > > 
> > > It'd be quite a bit easier to allow upper layers (e.g. XFS and ext4) to
> > > check for a queue flag.
> >
> > I think GENHD_FL_DAX is more appropriate since DAX does not use a request
> > queue, except for protecting the underlining device being disabled while
> > direct_access() is called (b2e0d1625e19).
> > 
> > About protecting direct_access, this patch assumes that the underlining
> > device cannot be disabled until dtr() is called.  Is this correct?  If
> > not, I will need to call dax_map_atomic().
>
> Kernel internal usages of dax should be using dax_map_atomic() to
> safely resolve device removal races.

Will do.  In such case, shall I move dax_[un]map_atomic() to block_dev.c and
rename them to bdev_dax_[un]map_atomic()?

Thanks,
-Toshi
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