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

From	Mike Snitzer <snitzer@redhat.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH 0/6] Support DAX for device-mapper dm-linear devices
Date	2016-06-21 20:30 +0200
Message-ID	<rMyAW-Xa-15@gated-at.bofh.it> (permalink)
References	(5 earlier) <rMfyi-5y7-29@gated-at.bofh.it> <rMfyi-5y7-27@gated-at.bofh.it> <rMg1j-5KE-5@gated-at.bofh.it> <rMudX-6uM-3@gated-at.bofh.it> <rMwfM-7MM-31@gated-at.bofh.it>
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On Tue, Jun 21 2016 at 11:44am -0400,
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).  

The devices in question have a request_queue.  All bio-based device have
a request_queue.

I don't have a big problem with GENHD_FL_DAX.  Just wanted to point out
that such block device capabilities are generally advertised in terms of
a QUEUE_FLAG.

> 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().

One of the big design considerations for DM that a DM device can be
suspended (with or without flush) and any new IO will be blocked until
the DM device is resumed.

So ideally DM should be able to have the same capability even if using
DAX.

But that is different than what commit b2e0d1625e19 is addressing.  For
DM, I wouldn't think you'd need the extra protections that
dax_map_atomic() is providing given that the underlying block device
lifetime is managed via DM core's dm_get_device/dm_put_device (see also:
dm.c:open_table_device/close_table_device).

Thread

[PATCH 0/6] Support DAX for device-mapper dm-linear devices Toshi Kani <toshi.kani@hpe.com> - 2016-06-14 00:40 +0200
  [PATCH 1/6] genhd: Add GENHD_FL_DAX to gendisk flags Toshi Kani <toshi.kani@hpe.com> - 2016-06-14 00:40 +0200
  [PATCH 4/6] dm-linear: Add linear_direct_access() Toshi Kani <toshi.kani@hpe.com> - 2016-06-14 00:40 +0200
  [PATCH 6/6] dm: Enable DAX support for mapper device Toshi Kani <toshi.kani@hpe.com> - 2016-06-14 00:40 +0200
  [PATCH 3/6] dm: Add dm_blk_direct_access() for mapped device Toshi Kani <toshi.kani@hpe.com> - 2016-06-14 00:40 +0200
  [PATCH 2/6] block: Check GENHD_FL_DAX for DAX capability Toshi Kani <toshi.kani@hpe.com> - 2016-06-14 00:40 +0200
  [PATCH 5/6] dm, dm-linear: Add dax_supported to dm_target Toshi Kani <toshi.kani@hpe.com> - 2016-06-14 00:40 +0200
  Re: [PATCH 0/6] Support DAX for device-mapper dm-linear devices Mike Snitzer <snitzer@redhat.com> - 2016-06-14 01:00 +0200
    Re: [PATCH 0/6] Support DAX for device-mapper dm-linear devices Mike Snitzer <snitzer@redhat.com> - 2016-06-20 20:30 +0200
      Re: [PATCH 0/6] Support DAX for device-mapper dm-linear devices Mike Snitzer <snitzer@redhat.com> - 2016-06-20 21:50 +0200
        Re: [PATCH 0/6] Support DAX for device-mapper dm-linear devices Mike Snitzer <snitzer@redhat.com> - 2016-06-20 23:50 +0200
          Re: [PATCH 0/6] Support DAX for device-mapper dm-linear devices "Kani, Toshimitsu" <toshi.kani@hpe.com> - 2016-06-21 00:10 +0200
            Re: [PATCH 0/6] Support DAX for device-mapper dm-linear devices Mike Snitzer <snitzer@redhat.com> - 2016-06-21 00:40 +0200
              Re: [PATCH 0/6] Support DAX for device-mapper dm-linear devices Mike Snitzer <snitzer@redhat.com> - 2016-06-21 15:50 +0200
                Re: [PATCH 0/6] Support DAX for device-mapper dm-linear devices "Kani, Toshimitsu" <toshi.kani@hpe.com> - 2016-06-21 18:00 +0200
                Re: [PATCH 0/6] Support DAX for device-mapper dm-linear devices "Kani, Toshimitsu" <toshi.kani@hpe.com> - 2016-06-21 18:10 +0200
                Re: [PATCH 0/6] Support DAX for device-mapper dm-linear devices Dan Williams <dan.j.williams@intel.com> - 2016-06-21 18:30 +0200
                Re: [PATCH 0/6] Support DAX for device-mapper dm-linear devices Dan Williams <dan.j.williams@intel.com> - 2016-06-21 18:50 +0200
                Re: [PATCH 0/6] Support DAX for device-mapper dm-linear devices "Kani, Toshimitsu" <toshi.kani@hpe.com> - 2016-06-21 19:20 +0200
                Re: [PATCH 0/6] Support DAX for device-mapper dm-linear devices "Kani, Toshimitsu" <toshi.kani@hpe.com> - 2016-06-21 19:00 +0200
                Re: [PATCH 0/6] Support DAX for device-mapper dm-linear devices Mike Snitzer <snitzer@redhat.com> - 2016-06-21 20:30 +0200
                Re: [PATCH 0/6] Support DAX for device-mapper dm-linear devices "Kani, Toshimitsu" <toshi.kani@hpe.com> - 2016-06-22 19:50 +0200
                Re: [PATCH 0/6] Support DAX for device-mapper dm-linear devices Dan Williams <dan.j.williams@intel.com> - 2016-06-22 21:20 +0200
                Re: [PATCH 0/6] Support DAX for device-mapper dm-linear devices "Kani, Toshimitsu" <toshi.kani@hpe.com> - 2016-06-22 22:20 +0200
                Re: [PATCH 0/6] Support DAX for device-mapper dm-linear devices Mike Snitzer <snitzer@redhat.com> - 2016-06-23 00:40 +0200
                Re: [PATCH 0/6] Support DAX for device-mapper dm-linear devices "Kani, Toshimitsu" <toshi.kani@hpe.com> - 2016-06-23 01:20 +0200
          Re: [PATCH 0/6] Support DAX for device-mapper dm-linear devices "Kani, Toshimitsu" <toshi.kani@hpe.com> - 2016-06-21 00:50 +0200
      Re: [PATCH 0/6] Support DAX for device-mapper dm-linear devices "Kani, Toshimitsu" <toshi.kani@hpe.com> - 2016-06-20 23:10 +0200
  Re: [PATCH 0/6] Support DAX for device-mapper dm-linear devices Dan Williams <dan.j.williams@intel.com> - 2016-06-14 01:20 +0200
    Re: [PATCH 0/6] Support DAX for device-mapper dm-linear devices "Kani, Toshimitsu" <toshi.kani@hpe.com> - 2016-06-14 02:00 +0200
      Re: [PATCH 0/6] Support DAX for device-mapper dm-linear devices Dan Williams <dan.j.williams@intel.com> - 2016-06-14 02:10 +0200
        Re: [PATCH 0/6] Support DAX for device-mapper dm-linear devices Dan Williams <dan.j.williams@intel.com> - 2016-06-14 09:40 +0200
      Re: [PATCH 0/6] Support DAX for device-mapper dm-linear devices Jeff Moyer <jmoyer@redhat.com> - 2016-06-14 16:00 +0200
        Re: [PATCH 0/6] Support DAX for device-mapper dm-linear devices Mike Snitzer <snitzer@redhat.com> - 2016-06-14 17:50 +0200
          Re: [PATCH 0/6] Support DAX for device-mapper dm-linear devices "Kani, Toshimitsu" <toshi.kani@hpe.com> - 2016-06-14 20:10 +0200
          Re: [PATCH 0/6] Support DAX for device-mapper dm-linear devices Jeff Moyer <jmoyer@redhat.com> - 2016-06-14 22:20 +0200
            Re: [PATCH 0/6] Support DAX for device-mapper dm-linear devices Mike Snitzer <snitzer@redhat.com> - 2016-06-15 03:50 +0200
              Re: [PATCH 0/6] Support DAX for device-mapper dm-linear devices Dan Williams <dan.j.williams@intel.com> - 2016-06-15 04:10 +0200
                Re: [PATCH 0/6] Support DAX for device-mapper dm-linear devices Mike Snitzer <snitzer@redhat.com> - 2016-06-15 04:40 +0200
        Re: [PATCH 0/6] Support DAX for device-mapper dm-linear devices "Kani, Toshimitsu" <toshi.kani@hpe.com> - 2016-06-14 18:00 +0200

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