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Subject: Re: [PATCH v4 5/5] nvdimm: Schedule device registration on node local
 to the device
To:     Dan Williams <dan.j.williams@intel.com>
Cc:     Linux MM <linux-mm@kvack.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-nvdimm <linux-nvdimm@lists.01.org>,
        Pasha Tatashin <pavel.tatashin@microsoft.com>,
        Michal Hocko <mhocko@suse.com>,
        Dave Jiang <dave.jiang@intel.com>,
        Ingo Molnar <mingo@kernel.org>,
        Dave Hansen <dave.hansen@intel.com>,
        =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= <jglisse@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Logan Gunthorpe <logang@deltatee.com>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
References: <20180920215824.19464.8884.stgit@localhost.localdomain>
 <20180920222951.19464.39241.stgit@localhost.localdomain>
 <CAPcyv4hAEOUOBU4GENaFOb-xXi33g_ugCexfmY3DrLH27Z6MKg@mail.gmail.com>
From:   Alexander Duyck <alexander.h.duyck@linux.intel.com>
Message-ID: <b7e87e64-95d7-5118-6c7d-ad78d68dc92e@linux.intel.com>
Date:   Thu, 20 Sep 2018 17:16:22 -0700
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On 9/20/2018 3:59 PM, Dan Williams wrote:
> On Thu, Sep 20, 2018 at 3:31 PM Alexander Duyck
> <alexander.h.duyck@linux.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@linux.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.