On Mon, 2016-06-13 at 16:18 -0700, Dan Williams wrote:
> Thanks Toshi!
>
> On Mon, Jun 13, 2016 at 3:21 PM, Toshi Kani <toshi.kani@xxxxxxx> 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?
I think this is a kernel restriction. When a block device is declared as
DAX capable, it should mean that the whole device is DAX capable. So, I
think we need to assure the same to a mapped device.
In LVM level, a volume group may contain both DAX and non-DAX capable
devices. There is no restriction for creating/extending a volume group.
> > 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?
Yes, I hope to extend further and raid0 is a good candidate.
Thanks,
-Toshi
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