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

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Message-ID: <CAPcyv4jdM1phR=kGoP2-7tfsVvbNe2C6hHNS5TD28ALGZQQTSw@mail.gmail.com>
Date:	Mon, 13 Jun 2016 16:18:18 -0700
From:	Dan Williams <dan.j.williams@...el.com>
To:	Toshi Kani <toshi.kani@....com>
Cc:	Alasdair Kergon <agk@...hat.com>,
	Mike Snitzer <snitzer@...hat.com>,
	Ross Zwisler <ross.zwisler@...ux.intel.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Jens Axboe <axboe@...nel.dk>,
	"linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
	dm-devel@...hat.com, linux-raid <linux-raid@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/6] Support DAX for device-mapper dm-linear devices

Thanks Toshi!

On Mon, Jun 13, 2016 at 3:21 PM, 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.

I don't mind this, but it seems a policy decision that the kernel does
not need to make.  A sufficiently sophisticated user could cope with
DAX being available at varying LBAs.  Would it be sufficient to move
this policy decision to userspace tooling?

> The direct_access interface is added to dm and dm-linear to map
> a request to a target device.

I had dm-linear and md-raid0 support on my list of things to look at,
did you have raid0 in your plans?