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

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Message-ID: <CAPcyv4ht8B7dHe1ckv5d=bOrRzCy3=ZDVSTD0rRsak_LYD8r8g@mail.gmail.com>
Date:	Tue, 21 Jun 2016 09:45:33 -0700
From:	Dan Williams <dan.j.williams@...el.com>
To:	"Kani, Toshimitsu" <toshi.kani@....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>,
	"snitzer@...hat.com" <snitzer@...hat.com>,
	"viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>,
	"axboe@...nel.dk" <axboe@...nel.dk>, "axboe@...com" <axboe@...com>,
	"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 Tue, Jun 21, 2016 at 9:35 AM, Kani, Toshimitsu <toshi.kani@....com> wrote:
> 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@....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@...hat.com> wrote:
>> > > >
>> > > > On Mon, Jun 20 2016 at  5:28pm -0400,
>> > > > Kani, Toshimitsu <toshi.kani@....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()?

Sounds good to me.  I know Jeff and Christoph don't like the current
calling convention of passing in a structure.  Just note that they
might ask you to change it back to a list of parameters if it moves to
bdev_dax_map_atomic().