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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>
 <b7e87e64-95d7-5118-6c7d-ad78d68dc92e@linux.intel.com>
 <CAPcyv4iE=mrvdfXQ94O1r_u1geLbxpF0so3_3z4JLky4SuUNdw@mail.gmail.com>
From:   Alexander Duyck <alexander.h.duyck@linux.intel.com>
Message-ID: <0d6525c1-2e8b-0e5d-7dae-193bf697a4ec@linux.intel.com>
Date:   Thu, 20 Sep 2018 18:33:26 -0700
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On 9/20/2018 5:36 PM, Dan Williams wrote:
> On Thu, Sep 20, 2018 at 5:26 PM Alexander Duyck
> <alexander.h.duyck@linux.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@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.
> 
> 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).
> 

Are you talking about pulling the scheduling out or just adding a node 
value to the nd_device_register call so it can be set directly from the 
caller?

If you wanted what I could do is pull the set_dev_node call from 
nvdimm_bus_uevent and place it in nd_device_register. That should stick 
as the node doesn't get overwritten by the parent if it is set after 
device_initialize. If I did that along with the parent bit I was already 
doing then all that would be left to do in is just use the dev_to_node 
call on the device itself.