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

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Date:	Wed, 22 Jun 2016 22:59:10 +0000
From:	"Kani, Toshimitsu" <toshi.kani@....com>
To:	"snitzer@...hat.com" <snitzer@...hat.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"sandeen@...hat.com" <sandeen@...hat.com>,
	"linux-nvdimm@...1.01.org" <linux-nvdimm@...1.01.org>,
	"agk@...hat.com" <agk@...hat.com>,
	"linux-raid@...r.kernel.org" <linux-raid@...r.kernel.org>,
	"viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>,
	"dan.j.williams@...el.com" <dan.j.williams@...el.com>,
	"axboe@...com" <axboe@...com>, "axboe@...nel.dk" <axboe@...nel.dk>,
	"ross.zwisler@...ux.intel.com" <ross.zwisler@...ux.intel.com>,
	"dm-devel@...hat.com" <dm-devel@...hat.com>
Subject: Re: [PATCH 0/6] Support DAX for device-mapper dm-linear devices

On Wed, 2016-06-22 at 18:38 -0400, Mike Snitzer wrote:
> On Wed, Jun 22 2016 at  4:16P -0400,
> Kani, Toshimitsu <toshi.kani@....com> wrote:
> > 
> > On Wed, 2016-06-22 at 12:15 -0700, Dan Williams wrote:
> > > 
> > > On Wed, Jun 22, 2016 at 10:44 AM, Kani, Toshimitsu <toshi.kani@....com>
> > > wrote:
> > > > 
> > > > On Tue, 2016-06-21 at 14:17 -0400, Mike Snitzer wrote:
> > > > > 
> > > > > On Tue, Jun 21 2016 at 11:44am -0400,
> > > > > Kani, Toshimitsu <toshi.kani@....com> wrote:
> > > > > > 
> > > > > > On Tue, 2016-06-21 at 09:41 -0400, Mike Snitzer wrote:
> > > > > > > 
> > > > > The devices in question have a request_queue.  All bio-based device
> > > > > have a request_queue.
> > > > 
> > > > DAX-capable devices have two operation modes, bio-based and DAX.  I
> > > > agree that bio-based operation is associated with a request queue, and
> > > > its capabilities should be set to it.  DAX, on the other hand, is
> > > > rather independent from 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.
> > > > 
> > > > I do not have a strong opinion, but feel a bit odd to associate DAX to
> > > > a request queue.
> > >
> > > Given that we do not support dax to a raw block device [1] it seems a
> > > gendisk flag is more misleading than request_queue flag that specifies
> > > what requests can be made of the device.
> > > 
> > > [1]: acc93d30d7d4 Revert "block: enable dax for raw block devices"
> >
> > Oh, I see.  I will change to use request_queue flag.
>
> I implemented the block patch for this yesterday but based on your
> feedback I stopped there (didn't carry the change through to the DM core
> and DM linear -- can easily do so tomorrow though).
> 
> Feel free to use this as a starting point and fix/extend and add a
> proper header:

Thanks Mike! I made similar changes as well. I will take yours and finish up
the rest. :)
-Toshi