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From:   Dan Williams <dan.j.williams@intel.com>
Date:   Thu, 17 Jan 2019 08:56:08 -0800
Message-ID: <CAPcyv4heNGQf4NHYrMzUdBRw2n3tE08bMaVKzgYrPYVaVDWE9Q@mail.gmail.com>
Subject: Re: [PATCH 4/4] dax: "Hotplug" persistent memory for use like normal RAM
To:     "Du, Fan" <fan.du@intel.com>
Cc:     Dave Hansen <dave.hansen@linux.intel.com>,
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On Wed, Jan 16, 2019 at 9:21 PM Du, Fan <fan.du@intel.com> wrote:
[..]
> >From: Dave Hansen <dave.hansen@linux.intel.com>
> >
> >Currently, a persistent memory region is "owned" by a device driver,
> >either the "Direct DAX" or "Filesystem DAX" drivers.  These drivers
> >allow applications to explicitly use persistent memory, generally
> >by being modified to use special, new libraries.
> >
> >However, this limits persistent memory use to applications which
> >*have* been modified.  To make it more broadly usable, this driver
> >"hotplugs" memory into the kernel, to be managed ad used just like
> >normal RAM would be.
> >
> >To make this work, management software must remove the device from
> >being controlled by the "Device DAX" infrastructure:
> >
> >       echo -n dax0.0 > /sys/bus/dax/drivers/device_dax/remove_id
> >       echo -n dax0.0 > /sys/bus/dax/drivers/device_dax/unbind
> >
> >and then bind it to this new driver:
> >
> >       echo -n dax0.0 > /sys/bus/dax/drivers/kmem/new_id
> >       echo -n dax0.0 > /sys/bus/dax/drivers/kmem/bind
>
> Is there any plan to introduce additional mode, e.g. "kmem" in the userspace
> ndctl tool to do the configuration?
>

Yes, but not to ndctl. The daxctl tool will grow a helper for this.
The policy of what device-dax instances should be hotplugged at system
init will be managed by a persistent configuration file and udev
rules.