linux-kernel - Re: [PATCH v2 1/3] arm64/numa: export memory_add_physaddr_to_nid as EXPORT_SYMBOL

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Message-ID: <c4ee0a94-c980-80ca-c43d-15729e1a3663@redhat.com>
Date:   Wed, 8 Jul 2020 08:59:18 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Mike Rapoport <rppt@...ux.ibm.com>,
        Dan Williams <dan.j.williams@...el.com>
Cc:     Justin He <Justin.He@....com>, Michal Hocko <mhocko@...nel.org>,
        Catalin Marinas <Catalin.Marinas@....com>,
        Will Deacon <will@...nel.org>,
        Vishal Verma <vishal.l.verma@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Baoquan He <bhe@...hat.com>,
        Chuhong Yuan <hslester96@...il.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
        Kaly Xin <Kaly.Xin@....com>
Subject: Re: [PATCH v2 1/3] arm64/numa: export memory_add_physaddr_to_nid as
 EXPORT_SYMBOL_GPL

On 08.07.20 08:22, Mike Rapoport wrote:
> On Tue, Jul 07, 2020 at 09:27:43PM -0700, Dan Williams wrote:
>> On Tue, Jul 7, 2020 at 9:08 PM Justin He <Justin.He@....com> wrote:
>> [..]
>>>> 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:
>>>>
>>>> int memory_add_physaddr_to_nid(u64 addr)
>>>> {
>>>>         unsigned long start_pfn, end_pfn, pfn = PHYS_PFN(addr);
>>>>         int nid;
>>>>
>>>>         for_each_online_node(nid) {
>>>>                 get_pfn_range_for_nid(nid, &start_pfn, &end_pfn);
>>>>                 if (pfn >= start_pfn && pfn <= end_pfn)
>>>>                         return nid;
>>>>         }
>>>>         return NUMA_NO_NODE;
>>>> }
>>>
>>> Thanks for your suggestion,
>>> Could I wrap the codes and let memory_add_physaddr_to_nid simply invoke
>>> phys_to_target_node()?
>>
>> I think it needs to be the reverse. phys_to_target_node() should call
>> memory_add_physaddr_to_nid() by default, but fall back to searching
>> reserved memory address ranges in memblock. See phys_to_target_node()
>> in arch/x86/mm/numa.c. That one uses numa_meminfo instead of memblock,
>> but the principle is the same i.e. that a target node may not be
>> represented in memblock.memory, but memblock.reserved. I'm working on
>> a patch to provide a function similar to get_pfn_range_for_nid() that
>> operates on reserved memory.
> 
> Do we really need yet another memblock iterator?
> I think only x86 has memory that is not in memblock.memory but only in
> memblock.reserved.

Reading about abusing the memblock allcoator once again in memory
hotplug paths makes me shiver.

-- 
Thanks,

David / dhildenb