Re: [PATCH v2 1/3] arm64/numa: export memory_add_physaddr_to_nid as EXPORT_SYMBOL_GPL

[David Hildenbrand]

On 08.07.20 08:56, Justin He wrote:
> Hi Dan
> 
>> -----Original Message-----
>> From: Dan Williams <dan.j.williams@xxxxxxxxx>
>> Sent: Wednesday, July 8, 2020 1:48 PM
>> To: Mike Rapoport <rppt@xxxxxxxxxxxxx>
>> Cc: Justin He <Justin.He@xxxxxxx>; Michal Hocko <mhocko@xxxxxxxxxx>; David
>> Hildenbrand <david@xxxxxxxxxx>; Catalin Marinas <Catalin.Marinas@xxxxxxx>;
>> Will Deacon <will@xxxxxxxxxx>; Vishal Verma <vishal.l.verma@xxxxxxxxx>;
>> Dave Jiang <dave.jiang@xxxxxxxxx>; Andrew Morton <akpm@linux-
>> foundation.org>; Baoquan He <bhe@xxxxxxxxxx>; Chuhong Yuan
>> <hslester96@xxxxxxxxx>; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; linux-
>> kernel@xxxxxxxxxxxxxxx; linux-mm@xxxxxxxxx; linux-nvdimm@xxxxxxxxxxxx;
>> Kaly Xin <Kaly.Xin@xxxxxxx>
>> Subject: Re: [PATCH v2 1/3] arm64/numa: export memory_add_physaddr_to_nid
>> as EXPORT_SYMBOL_GPL
>>
>> On Tue, Jul 7, 2020 at 10:33 PM Mike Rapoport <rppt@xxxxxxxxxxxxx> wrote:
>>>
>>> On Tue, Jul 07, 2020 at 08:56:36PM -0700, Dan Williams wrote:
>>>> On Tue, Jul 7, 2020 at 7:20 PM Justin He <Justin.He@xxxxxxx> wrote:
>>>>>
>>>>> Hi Michal and David
>>>>>
>>>>>> -----Original Message-----
>>>>>> From: Michal Hocko <mhocko@xxxxxxxxxx>
>>>>>> Sent: Tuesday, July 7, 2020 7:55 PM
>>>>>> To: Justin He <Justin.He@xxxxxxx>
>>>>>> Cc: Catalin Marinas <Catalin.Marinas@xxxxxxx>; Will Deacon
>>>>>> <will@xxxxxxxxxx>; Dan Williams <dan.j.williams@xxxxxxxxx>; Vishal
>> Verma
>>>>>> <vishal.l.verma@xxxxxxxxx>; Dave Jiang <dave.jiang@xxxxxxxxx>;
>> Andrew
>>>>>> Morton <akpm@xxxxxxxxxxxxxxxxxxxx>; Mike Rapoport
>> <rppt@xxxxxxxxxxxxx>;
>>>>>> Baoquan He <bhe@xxxxxxxxxx>; Chuhong Yuan <hslester96@xxxxxxxxx>;
>> linux-
>>>>>> arm-kernel@xxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
>> linux-
>>>>>> mm@xxxxxxxxx; linux-nvdimm@xxxxxxxxxxxx; Kaly Xin
>> <Kaly.Xin@xxxxxxx>
>>>>>> Subject: Re: [PATCH v2 1/3] arm64/numa: export
>> memory_add_physaddr_to_nid
>>>>>> as EXPORT_SYMBOL_GPL
>>>>>>
>>>>>> On Tue 07-07-20 13:59:15, Jia He wrote:
>>>>>>> This exports memory_add_physaddr_to_nid() for module driver to
>> use.
>>>>>>>
>>>>>>> memory_add_physaddr_to_nid() is a fallback option to get the nid
>> in case
>>>>>>> NUMA_NO_NID is detected.
>>>>>>>
>>>>>>> Suggested-by: David Hildenbrand <david@xxxxxxxxxx>
>>>>>>> Signed-off-by: Jia He <justin.he@xxxxxxx>
>>>>>>> ---
>>>>>>>  arch/arm64/mm/numa.c | 5 +++--
>>>>>>>  1 file changed, 3 insertions(+), 2 deletions(-)
>>>>>>>
>>>>>>> diff --git a/arch/arm64/mm/numa.c b/arch/arm64/mm/numa.c
>>>>>>> index aafcee3e3f7e..7eeb31740248 100644
>>>>>>> --- a/arch/arm64/mm/numa.c
>>>>>>> +++ b/arch/arm64/mm/numa.c
>>>>>>> @@ -464,10 +464,11 @@ void __init arm64_numa_init(void)
>>>>>>>
>>>>>>>  /*
>>>>>>>   * We hope that we will be hotplugging memory on nodes we
>> already know
>>>>>> about,
>>>>>>> - * such that acpi_get_node() succeeds and we never fall back to
>> this...
>>>>>>> + * such that acpi_get_node() succeeds. But when SRAT is not
>> present,
>>>>>> the node
>>>>>>> + * id may be probed as NUMA_NO_NODE by acpi, Here provide a
>> fallback
>>>>>> option.
>>>>>>>   */
>>>>>>>  int memory_add_physaddr_to_nid(u64 addr)
>>>>>>>  {
>>>>>>> -   pr_warn("Unknown node for memory at 0x%llx, assuming node
>> 0\n",
>>>>>> addr);
>>>>>>>     return 0;
>>>>>>>  }
>>>>>>> +EXPORT_SYMBOL_GPL(memory_add_physaddr_to_nid);
>>>>>>
>>>>>> Does it make sense to export a noop function? Wouldn't make more
>> sense
>>>>>> to simply make it static inline somewhere in a header? I haven't
>> checked
>>>>>> whether there is an easy way to do that sanely bu this just hit my
>> eyes.
>>>>>
>>>>> Okay, I can make a change in memory_hotplug.h, sth like:
>>>>> --- a/include/linux/memory_hotplug.h
>>>>> +++ b/include/linux/memory_hotplug.h
>>>>> @@ -149,13 +149,13 @@ int add_pages(int nid, unsigned long start_pfn,
>> unsigned long nr_pages,
>>>>>               struct mhp_params *params);
>>>>>  #endif /* ARCH_HAS_ADD_PAGES */
>>>>>
>>>>> -#ifdef CONFIG_NUMA
>>>>> -extern int memory_add_physaddr_to_nid(u64 start);
>>>>> -#else
>>>>> +#if !defined(CONFIG_NUMA) || !defined(memory_add_physaddr_to_nid)
>>>>>  static inline int memory_add_physaddr_to_nid(u64 start)
>>>>>  {
>>>>>         return 0;
>>>>>  }
>>>>> +#else
>>>>> +extern int memory_add_physaddr_to_nid(u64 start);
>>>>>  #endif
>>>>>
>>>>> And then check the memory_add_physaddr_to_nid() helper on all arches,
>>>>> if it is noop(return 0), I can simply remove it.
>>>>> if it is not noop, after the helper,
>>>>> #define memory_add_physaddr_to_nid
>>>>>
>>>>> What do you think of this proposal?
>>>>
>>>> Especially for architectures that use memblock info for numa info
>>>> (which seems to be everyone except x86) why not implement a generic
>>>> memory_add_physaddr_to_nid() that does:
>>>
>>> That would be only arm64.
>>>
>>
>> Darn, I saw ARCH_KEEP_MEMBLOCK and had delusions of grandeur that it
>> could solve my numa api woes. At least for x86 the problem is already
>> solved with reserved numa_meminfo, but now I'm trying to write generic
>> drivers that use those apis and finding these gaps on other archs.
> 
> Even on arm64, there is a dependency issue in dax_pmem kmem case.
> If dax pmem uses memory_add_physaddr_to_nid() to decide which node that
> memblock should add into, get_pfn_range_for_nid() might not have
> the correct memblock info at that time. That is, get_pfn_range_for_nid()
> can't get the correct memblock info before add_memory()
> 
> So IMO, memory_add_physaddr_to_nid() still have to implement as noop on
> arm64 (return 0) together with sh,s390x? Powerpc, x86,ia64 can use their
> own implementation. And phys_to_target_node() can use your suggested(
> for_each_online_node() ...)
> 
> What do you think of it? Thanks

You are trying to fix the "we only have one dummy node" AFAIU, so what
you propose here is certainly good enough for now.

-- 
Thanks,

David / dhildenb