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

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Date:   Wed, 12 Dec 2018 11:53:47 +0000
From:   Jonathan Cameron <jonathan.cameron@...wei.com>
To:     Robin Murphy <robin.murphy@....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 Wed, 12 Dec 2018 11:42:36 +0000
Jonathan Cameron <jonathan.cameron@...wei.com> 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. 
Ah found it in the arm64 core tree.  I'll pull that in and test.

> 
> 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).
> 
> 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;
> > +}
>