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

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Message-ID: <CAPcyv4inaZgmv=S36_DofA9prKhWg4KBNPkTvzSALO6Vtb9ddw@mail.gmail.com>
Date:   Wed, 8 Jul 2020 00:04:06 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     Mike Rapoport <rppt@...ux.ibm.com>, 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 Tue, Jul 7, 2020 at 11:59 PM David Hildenbrand <david@...hat.com> wrote:
>
> 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.

Technical reasoning please?

arm64 numa information is established from memblock data. It seems
counterproductive to ignore that fact if we're already touching
memory_add_physaddr_to_nid() and have a use case for a driver to call
it.