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Message-ID: <b226746e-fed1-ea18-f100-0a2c6c561d1f@arm.com>
Date: Mon, 27 May 2019 13:39:11 +0530
From: Anshuman Khandual <anshuman.khandual@....com>
To: David Hildenbrand <david@...hat.com>, linux-kernel@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org, akpm@...ux-foundation.org,
catalin.marinas@....com, will.deacon@....com
Cc: mark.rutland@....com, mhocko@...e.com, ira.weiny@...el.com,
cai@....pw, logang@...tatee.com, james.morse@....com,
cpandya@...eaurora.org, arunks@...eaurora.org,
dan.j.williams@...el.com, mgorman@...hsingularity.net,
osalvador@...e.de, ard.biesheuvel@....com
Subject: Re: [PATCH V4 4/4] arm64/mm: Enable memory hot remove
On 05/21/2019 03:50 PM, David Hildenbrand wrote:
> On 20.05.19 07:18, Anshuman Khandual wrote:
>> The arch code for hot-remove must tear down portions of the linear map and
>> vmemmap corresponding to memory being removed. In both cases the page
>> tables mapping these regions must be freed, and when sparse vmemmap is in
>> use the memory backing the vmemmap must also be freed.
>>
>> This patch adds a new remove_pagetable() helper which can be used to tear
>> down either region, and calls it from vmemmap_free() and
>> ___remove_pgd_mapping(). The sparse_vmap argument determines whether the
>> backing memory will be freed.
>>
>> While freeing intermediate level page table pages bail out if any of it's
>> entries are still valid. This can happen for partially filled kernel page
>> table either from a previously attempted failed memory hot add or while
>> removing an address range which does not span the entire page table page
>> range.
>>
>> The vmemmap region may share levels of table with the vmalloc region. Take
>> the kernel ptl so that we can safely free potentially-shared tables.
>>
>> While here update arch_add_memory() 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.
>>
>> Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
>> ---
>> arch/arm64/Kconfig | 3 +
>> arch/arm64/mm/mmu.c | 212 +++++++++++++++++++++++++++++++++++++++++++++++++++-
>> 2 files changed, 213 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
>> index 4780eb7..ce24427 100644
>> --- a/arch/arm64/Kconfig
>> +++ b/arch/arm64/Kconfig
>> @@ -267,6 +267,9 @@ config HAVE_GENERIC_GUP
>> config ARCH_ENABLE_MEMORY_HOTPLUG
>> def_bool y
>>
>> +config ARCH_ENABLE_MEMORY_HOTREMOVE
>> + def_bool y
>> +
>> config SMP
>> def_bool y
>>
>> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
>> index a1bfc44..0cf0d41 100644
>> --- a/arch/arm64/mm/mmu.c
>> +++ b/arch/arm64/mm/mmu.c
>> @@ -733,6 +733,187 @@ int kern_addr_valid(unsigned long addr)
>>
>> return pfn_valid(pte_pfn(pte));
>> }
>> +
>> +#ifdef CONFIG_MEMORY_HOTPLUG
>> +static void free_hotplug_page_range(struct page *page, ssize_t size)
>> +{
>> + WARN_ON(PageReserved(page));
>> + free_pages((unsigned long)page_address(page), get_order(size));
>> +}
>> +
>> +static void free_hotplug_pgtable_page(struct page *page)
>> +{
>> + free_hotplug_page_range(page, PAGE_SIZE);
>> +}
>> +
>> +static void free_pte_table(pte_t *ptep, pmd_t *pmdp, unsigned long addr)
>> +{
>> + struct page *page;
>> + int i;
>> +
>> + for (i = 0; i < PTRS_PER_PTE; i++) {
>> + if (!pte_none(ptep[i]))
>> + return;
>> + }
>> +
>> + page = pmd_page(READ_ONCE(*pmdp));
>> + pmd_clear(pmdp);
>> + __flush_tlb_kernel_pgtable(addr);
>> + free_hotplug_pgtable_page(page);
>> +}
>> +
>> +static void free_pmd_table(pmd_t *pmdp, pud_t *pudp, unsigned long addr)
>> +{
>> + struct page *page;
>> + int i;
>> +
>> + if (CONFIG_PGTABLE_LEVELS <= 2)
>> + return;
>> +
>> + for (i = 0; i < PTRS_PER_PMD; i++) {
>> + if (!pmd_none(pmdp[i]))
>> + return;
>> + }
>> +
>> + page = pud_page(READ_ONCE(*pudp));
>> + pud_clear(pudp);
>> + __flush_tlb_kernel_pgtable(addr);
>> + free_hotplug_pgtable_page(page);
>> +}
>> +
>> +static void free_pud_table(pud_t *pudp, pgd_t *pgdp, unsigned long addr)
>> +{
>> + struct page *page;
>> + int i;
>> +
>> + if (CONFIG_PGTABLE_LEVELS <= 3)
>> + return;
>> +
>> + for (i = 0; i < PTRS_PER_PUD; i++) {
>> + if (!pud_none(pudp[i]))
>> + return;
>> + }
>> +
>> + page = pgd_page(READ_ONCE(*pgdp));
>> + pgd_clear(pgdp);
>> + __flush_tlb_kernel_pgtable(addr);
>> + free_hotplug_pgtable_page(page);
>> +}
>> +
>> +static void
>> +remove_pte_table(pmd_t *pmdp, unsigned long addr,
>> + unsigned long end, bool sparse_vmap)
>> +{
>> + struct page *page;
>> + pte_t *ptep, pte;
>> + unsigned long start = addr;
>> +
>> + for (; addr < end; addr += PAGE_SIZE) {
>> + ptep = pte_offset_kernel(pmdp, addr);
>> + pte = READ_ONCE(*ptep);
>> +
>> + if (pte_none(pte))
>> + continue;
>> +
>> + WARN_ON(!pte_present(pte));
>> + if (sparse_vmap) {
>> + page = pte_page(pte);
>> + free_hotplug_page_range(page, PAGE_SIZE);
>> + }
>> + pte_clear(&init_mm, addr, ptep);
>> + }
>> + flush_tlb_kernel_range(start, end);
>> +}
>> +
>> +static void
>> +remove_pmd_table(pud_t *pudp, unsigned long addr,
>> + unsigned long end, bool sparse_vmap)
>> +{
>> + unsigned long next;
>> + struct page *page;
>> + pte_t *ptep_base;
>> + pmd_t *pmdp, pmd;
>> +
>> + for (; addr < end; addr = next) {
>> + next = pmd_addr_end(addr, end);
>> + pmdp = pmd_offset(pudp, addr);
>> + pmd = READ_ONCE(*pmdp);
>> +
>> + if (pmd_none(pmd))
>> + continue;
>> +
>> + WARN_ON(!pmd_present(pmd));
>> + if (pmd_sect(pmd)) {
>> + if (sparse_vmap) {
>> + page = pmd_page(pmd);
>> + free_hotplug_page_range(page, PMD_SIZE);
>> + }
>> + pmd_clear(pmdp);
>> + continue;
>> + }
>> + ptep_base = pte_offset_kernel(pmdp, 0UL);
>> + remove_pte_table(pmdp, addr, next, sparse_vmap);
>> + free_pte_table(ptep_base, pmdp, addr);
>> + }
>> +}
>> +
>> +static void
>> +remove_pud_table(pgd_t *pgdp, unsigned long addr,
>> + unsigned long end, bool sparse_vmap)
>> +{
>> + unsigned long next;
>> + struct page *page;
>> + pmd_t *pmdp_base;
>> + pud_t *pudp, pud;
>> +
>> + for (; addr < end; addr = next) {
>> + next = pud_addr_end(addr, end);
>> + pudp = pud_offset(pgdp, addr);
>> + pud = READ_ONCE(*pudp);
>> +
>> + if (pud_none(pud))
>> + continue;
>> +
>> + WARN_ON(!pud_present(pud));
>> + if (pud_sect(pud)) {
>> + if (sparse_vmap) {
>> + page = pud_page(pud);
>> + free_hotplug_page_range(page, PUD_SIZE);
>> + }
>> + pud_clear(pudp);
>> + continue;
>> + }
>> + pmdp_base = pmd_offset(pudp, 0UL);
>> + remove_pmd_table(pudp, addr, next, sparse_vmap);
>> + free_pmd_table(pmdp_base, pudp, addr);
>> + }
>> +}
>> +
>> +static void
>> +remove_pagetable(unsigned long start, unsigned long end, bool sparse_vmap)
>> +{
>> + unsigned long addr, next;
>> + pud_t *pudp_base;
>> + pgd_t *pgdp, pgd;
>> +
>> + spin_lock(&init_mm.page_table_lock);
>> + for (addr = start; addr < end; addr = next) {
>> + next = pgd_addr_end(addr, end);
>> + pgdp = pgd_offset_k(addr);
>> + pgd = READ_ONCE(*pgdp);
>> +
>> + if (pgd_none(pgd))
>> + continue;
>> +
>> + WARN_ON(!pgd_present(pgd));
>> + pudp_base = pud_offset(pgdp, 0UL);
>> + remove_pud_table(pgdp, addr, next, sparse_vmap);
>> + free_pud_table(pudp_base, pgdp, addr);
>> + }
>> + spin_unlock(&init_mm.page_table_lock);
>> +}
>> +#endif
>> +
>> #ifdef CONFIG_SPARSEMEM_VMEMMAP
>> #if !ARM64_SWAPPER_USES_SECTION_MAPS
>> int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node,
>> @@ -780,6 +961,9 @@ int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node,
>> void vmemmap_free(unsigned long start, unsigned long end,
>> struct vmem_altmap *altmap)
>> {
>> +#ifdef CONFIG_MEMORY_HOTPLUG
>> + remove_pagetable(start, end, true);
>> +#endif
>> }
>> #endif /* CONFIG_SPARSEMEM_VMEMMAP */
>>
>> @@ -1070,10 +1254,16 @@ 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, false);
>> +}
>> +
>> int arch_add_memory(int nid, u64 start, u64 size,
>> struct mhp_restrictions *restrictions)
>> {
>> - int flags = 0;
>> + int ret, flags = 0;
>>
>> if (rodata_full || debug_pagealloc_enabled())
>> flags = NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS;
>> @@ -1081,7 +1271,25 @@ int arch_add_memory(int nid, u64 start, u64 size,
>> __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,
>> restrictions);
>> + if (ret)
>> + __remove_pgd_mapping(swapper_pg_dir,
>> + __phys_to_virt(start), size);
>
> Nit: Indentation of the parameters looks really weird.
>
>> + return ret;
>> +}
>> +
>> +#ifdef CONFIG_MEMORY_HOTREMOVE
>> +void 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));
>> +
>> + __remove_pages(zone, start_pfn, nr_pages, altmap);
>> + __remove_pgd_mapping(swapper_pg_dir,
>> + __phys_to_virt(start), size);
>
> Dito, indentation of the parameters.
>
> For these two changes (arch_*_memory)
>
> Acked-by: David Hildenbrand <david@...hat.com>
Thanks David. The following change on this patch should fix the indentation
problem. If there are no other comments I will incorporate this and re-spin
the series once more.
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index 0cf0d41..a87ba18 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -1273,9 +1273,10 @@ int arch_add_memory(int nid, u64 start, u64 size,
ret = __add_pages(nid, start >> PAGE_SHIFT, size >> PAGE_SHIFT,
restrictions);
- if (ret)
- __remove_pgd_mapping(swapper_pg_dir,
- __phys_to_virt(start), size);
+ if (!ret)
+ return ret;
+
+ __remove_pgd_mapping(swapper_pg_dir, __phys_to_virt(start), size);
return ret;
}
@@ -1288,8 +1289,7 @@ void arch_remove_memory(int nid, u64 start, u64 size,
struct zone *zone = page_zone(pfn_to_page(start_pfn));
__remove_pages(zone, start_pfn, nr_pages, altmap);
- __remove_pgd_mapping(swapper_pg_dir,
- __phys_to_virt(start), size);
+ __remove_pgd_mapping(swapper_pg_dir, __phys_to_virt(start), size);
}
#endif
#endif
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