linux-kernel - Re: [PATCH v2] arm64: Add memory hotplug support

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Date:   Wed, 12 Dec 2018 11:49:23 +0000
From:   Robin Murphy <robin.murphy@....com>
To:     Jonathan Cameron <jonathan.cameron@...wei.com>
Cc:     will.deacon@....com, catalin.marinas@....com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        cyrilc@...inx.com, james.morse@....com, anshuman.khandual@....com,
        linux-mm@...ck.org
Subject: Re: [PATCH v2] arm64: Add memory hotplug support

On 12/12/2018 11:42, Jonathan Cameron wrote:
> On Tue, 11 Dec 2018 18:48:48 +0000
> Robin Murphy <robin.murphy@....com> wrote:
> 
>> Wire up the basic support for hot-adding memory. Since memory hotplug
>> is fairly tightly coupled to sparsemem, we tweak pfn_valid() to also
>> cross-check the presence of a section in the manner of the generic
>> implementation, before falling back to memblock to check for no-map
>> regions within a present section as before. By having arch_add_memory(()
>> create the linear mapping first, this then makes everything work in the
>> way that __add_section() expects.
>>
>> We expect hotplug to be ACPI-driven, so the swapper_pg_dir updates
>> should be safe from races by virtue of the global device hotplug lock.
>>
>> Signed-off-by: Robin Murphy <robin.murphy@....com>
> Hi Robin,
> 
> What tree is this against?
> 
> rodata_full doesn't seem be exist for me on 4.20-rc6.

Sorry, this is now based on the arm64 for-next/core branch - I was 
similarly confused when Will first mentioned rodata_full on v1 ;)

> With v1 I did the 'new node' test and it looked good except for an
> old cgroups warning that has always been there (and has been on my list
> to track down for a long time).

Great, thanks for testing!

Robin.

> 
> Jonathan
>> ---
>>
>> v2: Handle page-mappings-only cases appropriately
>>
>>   arch/arm64/Kconfig   |  3 +++
>>   arch/arm64/mm/init.c |  8 ++++++++
>>   arch/arm64/mm/mmu.c  | 17 +++++++++++++++++
>>   arch/arm64/mm/numa.c | 10 ++++++++++
>>   4 files changed, 38 insertions(+)
>>
>> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
>> index 4dbef530cf58..be423fda5cec 100644
>> --- a/arch/arm64/Kconfig
>> +++ b/arch/arm64/Kconfig
>> @@ -261,6 +261,9 @@ config ZONE_DMA32
>>   config HAVE_GENERIC_GUP
>>   	def_bool y
>>   
>> +config ARCH_ENABLE_MEMORY_HOTPLUG
>> +	def_bool y
>> +
>>   config SMP
>>   	def_bool y
>>   
>> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
>> index 6cde00554e9b..4bfe0fc9edac 100644
>> --- a/arch/arm64/mm/init.c
>> +++ b/arch/arm64/mm/init.c
>> @@ -291,6 +291,14 @@ int pfn_valid(unsigned long pfn)
>>   
>>   	if ((addr >> PAGE_SHIFT) != pfn)
>>   		return 0;
>> +
>> +#ifdef CONFIG_SPARSEMEM
>> +	if (pfn_to_section_nr(pfn) >= NR_MEM_SECTIONS)
>> +		return 0;
>> +
>> +	if (!valid_section(__nr_to_section(pfn_to_section_nr(pfn))))
>> +		return 0;
>> +#endif
>>   	return memblock_is_map_memory(addr);
>>   }
>>   EXPORT_SYMBOL(pfn_valid);
>> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
>> index 674c409a8ce4..da513a1facf4 100644
>> --- a/arch/arm64/mm/mmu.c
>> +++ b/arch/arm64/mm/mmu.c
>> @@ -1046,3 +1046,20 @@ int pud_free_pmd_page(pud_t *pudp, unsigned long addr)
>>   	pmd_free(NULL, table);
>>   	return 1;
>>   }
>> +
>> +#ifdef CONFIG_MEMORY_HOTPLUG
>> +int arch_add_memory(int nid, u64 start, u64 size, struct vmem_altmap *altmap,
>> +		    bool want_memblock)
>> +{
>> +	int flags = 0;
>> +
>> +	if (rodata_full || debug_pagealloc_enabled())
>> +		flags = NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS;
>> +
>> +	__create_pgd_mapping(swapper_pg_dir, start, __phys_to_virt(start),
>> +			     size, PAGE_KERNEL, pgd_pgtable_alloc, flags);
>> +
>> +	return __add_pages(nid, start >> PAGE_SHIFT, size >> PAGE_SHIFT,
>> +			   altmap, want_memblock);
>> +}
>> +#endif
>> diff --git a/arch/arm64/mm/numa.c b/arch/arm64/mm/numa.c
>> index 27a31efd9e8e..ae34e3a1cef1 100644
>> --- a/arch/arm64/mm/numa.c
>> +++ b/arch/arm64/mm/numa.c
>> @@ -466,3 +466,13 @@ void __init arm64_numa_init(void)
>>   
>>   	numa_init(dummy_numa_init);
>>   }
>> +
>> +/*
>> + * 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...
>> + */
>> +int memory_add_physaddr_to_nid(u64 addr)
>> +{
>> +	pr_warn("Unknown node for memory at 0x%llx, assuming node 0\n", addr);
>> +	return 0;
>> +}
> 
>