linux-kernel - Re: [PATCH v4 5/5] nvdimm: Schedule device registration on node local to the device

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Date:   Thu, 20 Sep 2018 17:36:44 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     alexander.h.duyck@...ux.intel.com
Cc:     Linux MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>,
        Pasha Tatashin <pavel.tatashin@...rosoft.com>,
        Michal Hocko <mhocko@...e.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Ingo Molnar <mingo@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Logan Gunthorpe <logang@...tatee.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCH v4 5/5] nvdimm: Schedule device registration on node local
 to the device

On Thu, Sep 20, 2018 at 5:26 PM Alexander Duyck
<alexander.h.duyck@...ux.intel.com> wrote:
>
> On 9/20/2018 3:59 PM, Dan Williams wrote:
> > On Thu, Sep 20, 2018 at 3:31 PM Alexander Duyck
> > <alexander.h.duyck@...ux.intel.com> wrote:
> >>
> >> This patch is meant to force the device registration for nvdimm devices to
> >> be closer to the actual device. This is achieved by using either the NUMA
> >> node ID of the region, or of the parent. By doing this we can have
> >> everything above the region based on the region, and everything below the
> >> region based on the nvdimm bus.
> >>
> >> One additional change I made is that we hold onto a reference to the parent
> >> while we are going through registration. By doing this we can guarantee we
> >> can complete the registration before we have the parent device removed.
> >>
> >> By guaranteeing NUMA locality I see an improvement of as high as 25% for
> >> per-node init of a system with 12TB of persistent memory.
> >>
> >> Signed-off-by: Alexander Duyck <alexander.h.duyck@...ux.intel.com>
> >> ---
> >>   drivers/nvdimm/bus.c |   19 +++++++++++++++++--
> >>   1 file changed, 17 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/drivers/nvdimm/bus.c b/drivers/nvdimm/bus.c
> >> index 8aae6dcc839f..ca935296d55e 100644
> >> --- a/drivers/nvdimm/bus.c
> >> +++ b/drivers/nvdimm/bus.c
> >> @@ -487,7 +487,9 @@ static void nd_async_device_register(void *d, async_cookie_t cookie)
> >>                  dev_err(dev, "%s: failed\n", __func__);
> >>                  put_device(dev);
> >>          }
> >> +
> >>          put_device(dev);
> >> +       put_device(dev->parent);
> >
> > Good catch. The child does not pin the parent until registration, but
> > we need to make sure the parent isn't gone while were waiting for the
> > registration work to run.
> >
> > Let's break this reference count fix out into its own separate patch,
> > because this looks to be covering a gap that may need to be
> > recommended for -stable.
>
> Okay, I guess I can do that.
>
> >
> >>
> >>   static void nd_async_device_unregister(void *d, async_cookie_t cookie)
> >> @@ -504,12 +506,25 @@ static void nd_async_device_unregister(void *d, async_cookie_t cookie)
> >>
> >>   void __nd_device_register(struct device *dev)
> >>   {
> >> +       int node;
> >> +
> >>          if (!dev)
> >>                  return;
> >> +
> >>          dev->bus = &nvdimm_bus_type;
> >> +       get_device(dev->parent);
> >>          get_device(dev);
> >> -       async_schedule_domain(nd_async_device_register, dev,
> >> -                       &nd_async_domain);
> >> +
> >> +       /*
> >> +        * For a region we can break away from the parent node,
> >> +        * otherwise for all other devices we just inherit the node from
> >> +        * the parent.
> >> +        */
> >> +       node = is_nd_region(dev) ? to_nd_region(dev)->numa_node :
> >> +                                  dev_to_node(dev->parent);
> >
> > Devices already automatically inherit the node of their parent, so I'm
> > not understanding why this is needed?
>
> That doesn't happen until you call device_add, which you don't call
> until nd_async_device_register. All that has been called on the device
> up to now is device_initialize which leaves the node at NUMA_NO_NODE.

Ooh, yeah, missed that. I think I'd prefer this policy to moved out to
where we set the dev->parent before calling __nd_device_register, or
at least a comment here about *why* we know region devices are special
(i.e. because the nd_region_desc specified the node at region creation
time).