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

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Date:	Mon, 20 Jun 2016 14:00:43 -0400
From:	Mike Snitzer <snitzer@...hat.com>
To:	Toshi Kani <toshi.kani@....com>
Cc:	axboe@...nel.dk, linux-nvdimm@...1.01.org,
	linux-kernel@...r.kernel.org, linux-raid@...r.kernel.org,
	dm-devel@...hat.com, viro@...iv.linux.org.uk,
	dan.j.williams@...el.com, ross.zwisler@...ux.intel.com,
	agk@...hat.com
Subject: Re: [PATCH 0/6] Support DAX for device-mapper dm-linear devices

On Mon, Jun 13 2016 at  6:57pm -0400,
Mike Snitzer <snitzer@...hat.com> wrote:

> On Mon, Jun 13 2016 at  6:21pm -0400,
> Toshi Kani <toshi.kani@....com> wrote:
> 
> > This patch-set adds DAX support to device-mapper dm-linear devices
> > used by LVM.  It works with LVM commands as follows:
> >  - Creation of a logical volume with all DAX capable devices (such
> >    as pmem) sets the logical volume DAX capable as well.
> >  - Once a logical volume is set to DAX capable, the volume may not
> >    be extended with non-DAX capable devices.
> > 
> > The direct_access interface is added to dm and dm-linear to map
> > a request to a target device.
> > 
> >  - Patch 1-2 introduce GENHD_FL_DAX flag to indicate DAX capability.
> >  - Patch 3-4 add direct_access functions to dm and dm-linear.
> >  - Patch 5-6 set GENHD_FL_DAX to dm when all targets are DAX capable.
> > 
> > ---
> > Toshi Kani (6):
> >  1/6 genhd: Add GENHD_FL_DAX to gendisk flags
> >  2/6 block: Check GENHD_FL_DAX for DAX capability
> >  3/6 dm: Add dm_blk_direct_access() for mapped device
> >  4/6 dm-linear: Add linear_direct_access()
> >  5/6 dm, dm-linear: Add dax_supported to dm_target
> >  6/6 dm: Enable DAX support for mapper device
> 
> Thanks a lot for doing this.  I recently added it to my TODO so your
> patches come at a great time.
> 
> I'll try to get to reviewing/testing your work by the end of this week.

I rebased your patches on linux-dm.git's 'for-next' (which includes what
I've already staged for the 4.8 merge window).  And I folded/changed
some of the DM patches so that there are only 2 now (1 for DM core and 1
for dm-linear).  Please see the 4 topmost commits in my 'wip' here:

http://git.kernel.org/cgit/linux/kernel/git/snitzer/linux.git/log/?h=wip

Feel free to pick these patches up to use as the basis for continued
work or re-posting of this set.. either that or I could post them as v2
on your behalf.

As for testing, I've verified that basic IO works to a pmem-based DM
linear device and that mixed table types are rejected as expected.

Mike