linux-kernel - Re: [PATCH 2/2] nvdimm: Set device node in nd_device

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Date:   Tue, 25 Sep 2018 14:32:58 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     alexander.h.duyck@...ux.intel.com
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>,
        Vishal L Verma <vishal.l.verma@...el.com>,
        Dave Jiang <dave.jiang@...el.com>, zwisler@...nel.org
Subject: Re: [PATCH 2/2] nvdimm: Set device node in nd_device_register

On Tue, Sep 25, 2018 at 2:11 PM Alexander Duyck
<alexander.h.duyck@...ux.intel.com> wrote:
>
>
>
> On 9/25/2018 2:08 PM, Dan Williams wrote:
> > On Tue, Sep 25, 2018 at 1:56 PM Alexander Duyck
> > <alexander.h.duyck@...ux.intel.com> wrote:
> >>
> >> This change makes it so that we don't repeatedly overwrite the device node
> >> for nvdimm regions. The earliest we can set the node is immediately after
> >> calling device init, so I have moved the code there so we can avoid
> >> rewriting the node with each uevent.
> >>
> >> Signed-off-by: Alexander Duyck <alexander.h.duyck@...ux.intel.com>
> >> ---
> >>   drivers/nvdimm/bus.c |   16 ++++++++++------
> >>   1 file changed, 10 insertions(+), 6 deletions(-)
> >>
> >> diff --git a/drivers/nvdimm/bus.c b/drivers/nvdimm/bus.c
> >> index 9148015ed803..96f4d0e1706a 100644
> >> --- a/drivers/nvdimm/bus.c
> >> +++ b/drivers/nvdimm/bus.c
> >> @@ -54,12 +54,6 @@ static int to_nd_device_type(struct device *dev)
> >>
> >>   static int nvdimm_bus_uevent(struct device *dev, struct kobj_uevent_env *env)
> >>   {
> >> -       /*
> >> -        * Ensure that region devices always have their numa node set as
> >> -        * early as possible.
> >> -        */
> >> -       if (is_nd_region(dev))
> >> -               set_dev_node(dev, to_nd_region(dev)->numa_node);
> >>          return add_uevent_var(env, "MODALIAS=" ND_DEVICE_MODALIAS_FMT,
> >>                          to_nd_device_type(dev));
> >>   }
> >> @@ -519,6 +513,16 @@ void __nd_device_register(struct device *dev)
> >>   void nd_device_register(struct device *dev)
> >>   {
> >>          device_initialize(dev);
> >> +
> >> +       /*
> >> +        * Ensure that region devices always have their NUMA node set as
> >> +        * early as possible. This way we are able to make certain that any
> >> +        * memory associated with the creation and the creation itself of
> >> +        * the region is associated with the correct node.
> >> +        */
> >> +       if (is_nd_region(dev))
> >> +               set_dev_node(dev, to_nd_region(dev)->numa_node);
> >> +
> >>          __nd_device_register(dev);
> >
> > Any reason to not put this inside __nd_device_register()? If you're ok
> > with that I can just fix up when applying.
>
> I put it here since regions never call __nd_device_register directly,
> they always call nd_device_register. I figured that by placing it here
> we reduce the impact of this on the other devices that aren't going to
> need it.

I can't imagine there's much of an impact because we're already
reading the cacheline that has dev->parent so dev->type is already
there. If we're going to add support for looking up the parent node to
schedule namespace registration work to the proper core I would expect
that to appear in the __nd_device_register() common code as well.

In general the only consideration for calling nd_device_register() vs
__nd_device_register() is whether or not you want a
device_initialize() to occur.