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SubjectRe: [PATCH 2/6] arm64/mm: Enable memory hot remove
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Date
[ +Steve ]

Hi Anshuman,

On 03/04/2019 05:30, Anshuman Khandual wrote:
> Memory removal from an arch perspective involves tearing down two different
> kernel based mappings i.e vmemmap and linear while releasing related page
> table pages allocated for the physical memory range to be removed.
>
> Define a common kernel page table tear down helper remove_pagetable() which
> can be used to unmap given kernel virtual address range. In effect it can
> tear down both vmemap or kernel linear mappings. This new helper is called
> from both vmemamp_free() and ___remove_pgd_mapping() during memory removal.
> The argument 'direct' here identifies kernel linear mappings.
>
> Vmemmap mappings page table pages are allocated through sparse mem helper
> functions like vmemmap_alloc_block() which does not cycle the pages through
> pgtable_page_ctor() constructs. Hence while removing it skips corresponding
> destructor construct pgtable_page_dtor().
>
> While here update arch_add_mempory() to handle __add_pages() failures by
> just unmapping recently added kernel linear mapping. Now enable memory hot
> remove on arm64 platforms by default with ARCH_ENABLE_MEMORY_HOTREMOVE.
>
> This implementation is overall inspired from kernel page table tear down
> procedure on X86 architecture.

A bit of a nit, but since this depends on at least patch #4 to work
properly, it would be good to reorder the series appropriately.
> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
> ---
> arch/arm64/Kconfig | 3 +
> arch/arm64/include/asm/pgtable.h | 14 +++
> arch/arm64/mm/mmu.c | 227 ++++++++++++++++++++++++++++++++++++++-
> 3 files changed, 241 insertions(+), 3 deletions(-)
>
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index a2418fb..db3e625 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -266,6 +266,9 @@ config HAVE_GENERIC_GUP
> config ARCH_ENABLE_MEMORY_HOTPLUG
> def_bool y
>
> +config ARCH_ENABLE_MEMORY_HOTREMOVE
> + def_bool y
> +
> config ARCH_MEMORY_PROBE
> bool "Enable /sys/devices/system/memory/probe interface"
> depends on MEMORY_HOTPLUG
> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> index de70c1e..858098e 100644
> --- a/arch/arm64/include/asm/pgtable.h
> +++ b/arch/arm64/include/asm/pgtable.h
> @@ -355,6 +355,18 @@ static inline int pmd_protnone(pmd_t pmd)
> }
> #endif
>
> +#if (CONFIG_PGTABLE_LEVELS > 2)
> +#define pmd_large(pmd) (pmd_val(pmd) && !(pmd_val(pmd) & PMD_TABLE_BIT))
> +#else
> +#define pmd_large(pmd) 0
> +#endif
> +
> +#if (CONFIG_PGTABLE_LEVELS > 3)
> +#define pud_large(pud) (pud_val(pud) && !(pud_val(pud) & PUD_TABLE_BIT))
> +#else
> +#define pud_large(pmd) 0
> +#endif

These seem rather different from the versions that Steve is proposing in
the generic pagewalk series - can you reach an agreement on which
implementation is preferred?

> +
> /*
> * THP definitions.
> */
> @@ -555,6 +567,7 @@ static inline phys_addr_t pud_page_paddr(pud_t pud)
>
> #else
>
> +#define pmd_index(addr) 0
> #define pud_page_paddr(pud) ({ BUILD_BUG(); 0; })
>
> /* Match pmd_offset folding in <asm/generic/pgtable-nopmd.h> */
> @@ -612,6 +625,7 @@ static inline phys_addr_t pgd_page_paddr(pgd_t pgd)
>
> #else
>
> +#define pud_index(adrr) 0
> #define pgd_page_paddr(pgd) ({ BUILD_BUG(); 0;})
>
> /* Match pud_offset folding in <asm/generic/pgtable-nopud.h> */
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index e97f018..ae0777b 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -714,6 +714,198 @@ int kern_addr_valid(unsigned long addr)
>
> return pfn_valid(pte_pfn(pte));
> }
> +
> +#ifdef CONFIG_MEMORY_HOTPLUG
> +static void __meminit free_pagetable(struct page *page, int order)

Do these need to be __meminit? AFAICS it's effectively redundant with
the containing #ifdef, and removal feels like it's inherently a
later-than-init thing anyway.

> +{
> + unsigned long magic;
> + unsigned int nr_pages = 1 << order;
> +
> + if (PageReserved(page)) {
> + __ClearPageReserved(page);
> +
> + magic = (unsigned long)page->freelist;
> + if (magic == SECTION_INFO || magic == MIX_SECTION_INFO) {
> + while (nr_pages--)
> + put_page_bootmem(page++);
> + } else
> + while (nr_pages--)
> + free_reserved_page(page++);
> + } else
> + free_pages((unsigned long)page_address(page), order);
> +}
> +
> +#if (CONFIG_PGTABLE_LEVELS > 2)
> +static void __meminit free_pte_table(pte_t *pte_start, pmd_t *pmd, bool direct)
> +{
> + pte_t *pte;
> + int i;
> +
> + for (i = 0; i < PTRS_PER_PTE; i++) {
> + pte = pte_start + i;
> + if (!pte_none(*pte))
> + return;
> + }
> +
> + if (direct)
> + pgtable_page_dtor(pmd_page(*pmd));
> + free_pagetable(pmd_page(*pmd), 0);
> + spin_lock(&init_mm.page_table_lock);
> + pmd_clear(pmd);
> + spin_unlock(&init_mm.page_table_lock);
> +}
> +#else
> +static void __meminit free_pte_table(pte_t *pte_start, pmd_t *pmd, bool direct)
> +{
> +}
> +#endif
> +
> +#if (CONFIG_PGTABLE_LEVELS > 3)
> +static void __meminit free_pmd_table(pmd_t *pmd_start, pud_t *pud, bool direct)
> +{
> + pmd_t *pmd;
> + int i;
> +
> + for (i = 0; i < PTRS_PER_PMD; i++) {
> + pmd = pmd_start + i;
> + if (!pmd_none(*pmd))
> + return;
> + }
> +
> + if (direct)
> + pgtable_page_dtor(pud_page(*pud));
> + free_pagetable(pud_page(*pud), 0);
> + spin_lock(&init_mm.page_table_lock);
> + pud_clear(pud);
> + spin_unlock(&init_mm.page_table_lock);
> +}
> +
> +static void __meminit free_pud_table(pud_t *pud_start, pgd_t *pgd, bool direct)
> +{
> + pud_t *pud;
> + int i;
> +
> + for (i = 0; i < PTRS_PER_PUD; i++) {
> + pud = pud_start + i;
> + if (!pud_none(*pud))
> + return;
> + }
> +
> + if (direct)
> + pgtable_page_dtor(pgd_page(*pgd));
> + free_pagetable(pgd_page(*pgd), 0);
> + spin_lock(&init_mm.page_table_lock);
> + pgd_clear(pgd);
> + spin_unlock(&init_mm.page_table_lock);
> +}
> +#else
> +static void __meminit free_pmd_table(pmd_t *pmd_start, pud_t *pud, bool direct)
> +{
> +}
> +
> +static void __meminit free_pud_table(pud_t *pud_start, pgd_t *pgd, bool direct)
> +{
> +}
> +#endif
> +
> +static void __meminit
> +remove_pte_table(pte_t *pte_start, unsigned long addr,
> + unsigned long end, bool direct)
> +{
> + pte_t *pte;
> +
> + pte = pte_start + pte_index(addr);
> + for (; addr < end; addr += PAGE_SIZE, pte++) {
> + if (!pte_present(*pte))
> + continue;
> +
> + if (!direct)
> + free_pagetable(pte_page(*pte), 0);
> + spin_lock(&init_mm.page_table_lock);
> + pte_clear(&init_mm, addr, pte);
> + spin_unlock(&init_mm.page_table_lock);
> + }
> +}
> +
> +static void __meminit
> +remove_pmd_table(pmd_t *pmd_start, unsigned long addr,
> + unsigned long end, bool direct)
> +{
> + unsigned long next;
> + pte_t *pte_base;
> + pmd_t *pmd;
> +
> + pmd = pmd_start + pmd_index(addr);
> + for (; addr < end; addr = next, pmd++) {
> + next = pmd_addr_end(addr, end);
> + if (!pmd_present(*pmd))
> + continue;
> +
> + if (pmd_large(*pmd)) {
> + if (!direct)
> + free_pagetable(pmd_page(*pmd),
> + get_order(PMD_SIZE));
> + spin_lock(&init_mm.page_table_lock);
> + pmd_clear(pmd);
> + spin_unlock(&init_mm.page_table_lock);
> + continue;
> + }
> + pte_base = pte_offset_kernel(pmd, 0UL);
> + remove_pte_table(pte_base, addr, next, direct);
> + free_pte_table(pte_base, pmd, direct);
> + }
> +}
> +
> +static void __meminit
> +remove_pud_table(pud_t *pud_start, unsigned long addr,
> + unsigned long end, bool direct)
> +{
> + unsigned long next;
> + pmd_t *pmd_base;
> + pud_t *pud;
> +
> + pud = pud_start + pud_index(addr);
> + for (; addr < end; addr = next, pud++) {
> + next = pud_addr_end(addr, end);
> + if (!pud_present(*pud))
> + continue;
> +
> + if (pud_large(*pud)) {
> + if (!direct)
> + free_pagetable(pud_page(*pud),
> + get_order(PUD_SIZE));
> + spin_lock(&init_mm.page_table_lock);
> + pud_clear(pud);
> + spin_unlock(&init_mm.page_table_lock);
> + continue;
> + }
> + pmd_base = pmd_offset(pud, 0UL);
> + remove_pmd_table(pmd_base, addr, next, direct);
> + free_pmd_table(pmd_base, pud, direct);
> + }
> +}
> +
> +static void __meminit
> +remove_pagetable(unsigned long start, unsigned long end, bool direct)
> +{
> + unsigned long addr, next;
> + pud_t *pud_base;
> + pgd_t *pgd;
> +
> + for (addr = start; addr < end; addr = next) {
> + next = pgd_addr_end(addr, end);
> + pgd = pgd_offset_k(addr);
> + if (!pgd_present(*pgd))
> + continue;
> +
> + pud_base = pud_offset(pgd, 0UL);
> + remove_pud_table(pud_base, addr, next, direct);
> + free_pud_table(pud_base, pgd, direct);
> + }
> + flush_tlb_kernel_range(start, end);
> +}
> +#endif
> +
> #ifdef CONFIG_SPARSEMEM_VMEMMAP
> #if !ARM64_SWAPPER_USES_SECTION_MAPS
> int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node,
> @@ -758,9 +950,12 @@ int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node,
> return 0;
> }
> #endif /* CONFIG_ARM64_64K_PAGES */
> -void vmemmap_free(unsigned long start, unsigned long end,
> +void __ref vmemmap_free(unsigned long start, unsigned long end,

Why is the __ref needed? Presumably it's avoidable by addressing the
__meminit thing above.

> struct vmem_altmap *altmap)
> {
> +#ifdef CONFIG_MEMORY_HOTPLUG
> + remove_pagetable(start, end, false);
> +#endif
> }
> #endif /* CONFIG_SPARSEMEM_VMEMMAP */
>
> @@ -1046,10 +1241,16 @@ int p4d_free_pud_page(p4d_t *p4d, unsigned long addr)
> }
>
> #ifdef CONFIG_MEMORY_HOTPLUG
> +static void __remove_pgd_mapping(pgd_t *pgdir, unsigned long start, u64 size)
> +{
> + WARN_ON(pgdir != init_mm.pgd);
> + remove_pagetable(start, start + size, true);
> +}
> +
> int arch_add_memory(int nid, u64 start, u64 size, struct vmem_altmap *altmap,
> bool want_memblock)
> {
> - int flags = 0;
> + int flags = 0, ret = 0;

Initialising ret here is unnecessary.

Robin.

>
> if (rodata_full || debug_pagealloc_enabled())
> flags = NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS;
> @@ -1057,7 +1258,27 @@ int arch_add_memory(int nid, u64 start, u64 size, struct vmem_altmap *altmap,
> __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,
> + ret = __add_pages(nid, start >> PAGE_SHIFT, size >> PAGE_SHIFT,
> altmap, want_memblock);
> + if (ret)
> + __remove_pgd_mapping(swapper_pg_dir,
> + __phys_to_virt(start), size);
> + return ret;
> }
> +
> +#ifdef CONFIG_MEMORY_HOTREMOVE
> +int arch_remove_memory(int nid, u64 start, u64 size, struct vmem_altmap *altmap)
> +{
> + unsigned long start_pfn = start >> PAGE_SHIFT;
> + unsigned long nr_pages = size >> PAGE_SHIFT;
> + struct zone *zone = page_zone(pfn_to_page(start_pfn));
> + int ret;
> +
> + ret = __remove_pages(zone, start_pfn, nr_pages, altmap);
> + if (!ret)
> + __remove_pgd_mapping(swapper_pg_dir,
> + __phys_to_virt(start), size);
> + return ret;
> +}
> +#endif
> #endif
>

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