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SubjectRe: [PATCH v5 08/14] memory-hotplug: Common APIs to support page tables hot-remove
On 2012/12/24 20:09, Tang Chen wrote:

> From: Wen Congyang <wency@cn.fujitsu.com>
>
> When memory is removed, the corresponding pagetables should alse be removed.
> This patch introduces some common APIs to support vmemmap pagetable and x86_64
> architecture pagetable removing.
>
> All pages of virtual mapping in removed memory cannot be freedi if some pages
> used as PGD/PUD includes not only removed memory but also other memory. So the
> patch uses the following way to check whether page can be freed or not.
>
> 1. When removing memory, the page structs of the revmoved memory are filled
> with 0FD.
> 2. All page structs are filled with 0xFD on PT/PMD, PT/PMD can be cleared.
> In this case, the page used as PT/PMD can be freed.
>
> Signed-off-by: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
> Signed-off-by: Jianguo Wu <wujianguo@huawei.com>
> Signed-off-by: Wen Congyang <wency@cn.fujitsu.com>
> Signed-off-by: Tang Chen <tangchen@cn.fujitsu.com>
> ---
> arch/x86/include/asm/pgtable_types.h | 1 +
> arch/x86/mm/init_64.c | 297 ++++++++++++++++++++++++++++++++++
> arch/x86/mm/pageattr.c | 47 +++---
> include/linux/bootmem.h | 1 +
> 4 files changed, 324 insertions(+), 22 deletions(-)
>
> diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h
> index 3c32db8..4b6fd2a 100644
> --- a/arch/x86/include/asm/pgtable_types.h
> +++ b/arch/x86/include/asm/pgtable_types.h
> @@ -352,6 +352,7 @@ static inline void update_page_count(int level, unsigned long pages) { }
> * as a pte too.
> */
> extern pte_t *lookup_address(unsigned long address, unsigned int *level);
> +extern int __split_large_page(pte_t *kpte, unsigned long address, pte_t *pbase);
>
> #endif /* !__ASSEMBLY__ */
>
> diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
> index aeaa27e..b30df3c 100644
> --- a/arch/x86/mm/init_64.c
> +++ b/arch/x86/mm/init_64.c
> @@ -682,6 +682,303 @@ int arch_add_memory(int nid, u64 start, u64 size)
> }
> EXPORT_SYMBOL_GPL(arch_add_memory);
>
> +#define PAGE_INUSE 0xFD
> +
> +static void __meminit free_pagetable(struct page *page, int order)
> +{
> + struct zone *zone;
> + bool bootmem = false;
> + unsigned long magic;
> +
> + /* bootmem page has reserved flag */
> + if (PageReserved(page)) {
> + __ClearPageReserved(page);
> + bootmem = true;
> +
> + magic = (unsigned long)page->lru.next;
> + if (magic == SECTION_INFO || magic == MIX_SECTION_INFO)
> + put_page_bootmem(page);

Hi Tang,

For removing memmap of sparse-vmemmap, in cpu_has_pse case, if magic == SECTION_INFO,
the order will be get_order(PMD_SIZE), so we need a loop here to put all the 512 pages.

Thanks,
Jianguo Wu

> + else
> + __free_pages_bootmem(page, order);
> + } else
> + free_pages((unsigned long)page_address(page), order);
> +
> + /*
> + * SECTION_INFO pages and MIX_SECTION_INFO pages
> + * are all allocated by bootmem.
> + */
> + if (bootmem) {
> + zone = page_zone(page);
> + zone_span_writelock(zone);
> + zone->present_pages++;
> + zone_span_writeunlock(zone);
> + totalram_pages++;
> + }
> +}
> +
> +static void __meminit free_pte_table(pte_t *pte_start, pmd_t *pmd)
> +{
> + pte_t *pte;
> + int i;
> +
> + for (i = 0; i < PTRS_PER_PTE; i++) {
> + pte = pte_start + i;
> + if (pte_val(*pte))
> + return;
> + }
> +
> + /* free a pte talbe */
> + free_pagetable(pmd_page(*pmd), 0);
> + spin_lock(&init_mm.page_table_lock);
> + pmd_clear(pmd);
> + spin_unlock(&init_mm.page_table_lock);
> +}
> +
> +static void __meminit free_pmd_table(pmd_t *pmd_start, pud_t *pud)
> +{
> + pmd_t *pmd;
> + int i;
> +
> + for (i = 0; i < PTRS_PER_PMD; i++) {
> + pmd = pmd_start + i;
> + if (pmd_val(*pmd))
> + return;
> + }
> +
> + /* free a pmd talbe */
> + free_pagetable(pud_page(*pud), 0);
> + spin_lock(&init_mm.page_table_lock);
> + pud_clear(pud);
> + spin_unlock(&init_mm.page_table_lock);
> +}
> +
> +/* Return true if pgd is changed, otherwise return false. */
> +static bool __meminit free_pud_table(pud_t *pud_start, pgd_t *pgd)
> +{
> + pud_t *pud;
> + int i;
> +
> + for (i = 0; i < PTRS_PER_PUD; i++) {
> + pud = pud_start + i;
> + if (pud_val(*pud))
> + return false;
> + }
> +
> + /* free a pud table */
> + free_pagetable(pgd_page(*pgd), 0);
> + spin_lock(&init_mm.page_table_lock);
> + pgd_clear(pgd);
> + spin_unlock(&init_mm.page_table_lock);
> +
> + return true;
> +}
> +
> +static void __meminit
> +remove_pte_table(pte_t *pte_start, unsigned long addr, unsigned long end,
> + bool direct)
> +{
> + unsigned long next, pages = 0;
> + pte_t *pte;
> + void *page_addr;
> + phys_addr_t phys_addr;
> +
> + pte = pte_start + pte_index(addr);
> + for (; addr < end; addr = next, pte++) {
> + next = (addr + PAGE_SIZE) & PAGE_MASK;
> + if (next > end)
> + next = end;
> +
> + if (!pte_present(*pte))
> + continue;
> +
> + /*
> + * We mapped [0,1G) memory as identity mapping when
> + * initializing, in arch/x86/kernel/head_64.S. These
> + * pagetables cannot be removed.
> + */
> + phys_addr = pte_val(*pte) + (addr & PAGE_MASK);
> + if (phys_addr < (phys_addr_t)0x40000000)
> + return;
> +
> + if (IS_ALIGNED(addr, PAGE_SIZE) &&
> + IS_ALIGNED(next, PAGE_SIZE)) {
> + if (!direct) {
> + free_pagetable(pte_page(*pte), 0);
> + pages++;
> + }
> +
> + spin_lock(&init_mm.page_table_lock);
> + pte_clear(&init_mm, addr, pte);
> + spin_unlock(&init_mm.page_table_lock);
> + } else {
> + /*
> + * If we are not removing the whole page, it means
> + * other ptes in this page are being used and we canot
> + * remove them. So fill the unused ptes with 0xFD, and
> + * remove the page when it is wholly filled with 0xFD.
> + */
> + memset((void *)addr, PAGE_INUSE, next - addr);
> + page_addr = page_address(pte_page(*pte));
> +
> + if (!memchr_inv(page_addr, PAGE_INUSE, PAGE_SIZE)) {
> + free_pagetable(pte_page(*pte), 0);
> + pages++;
> +
> + spin_lock(&init_mm.page_table_lock);
> + pte_clear(&init_mm, addr, pte);
> + spin_unlock(&init_mm.page_table_lock);
> + }
> + }
> + }
> +
> + /* Call free_pte_table() in remove_pmd_table(). */
> + flush_tlb_all();
> + if (direct)
> + update_page_count(PG_LEVEL_4K, -pages);
> +}
> +
> +static void __meminit
> +remove_pmd_table(pmd_t *pmd_start, unsigned long addr, unsigned long end,
> + bool direct)
> +{
> + unsigned long pte_phys, next, pages = 0;
> + 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 (IS_ALIGNED(addr, PMD_SIZE) &&
> + IS_ALIGNED(next, PMD_SIZE)) {
> + if (!direct) {
> + free_pagetable(pmd_page(*pmd),
> + get_order(PMD_SIZE));
> + pages++;
> + }
> +
> + spin_lock(&init_mm.page_table_lock);
> + pmd_clear(pmd);
> + spin_unlock(&init_mm.page_table_lock);
> + continue;
> + }
> +
> + /*
> + * We use 2M page, but we need to remove part of them,
> + * so split 2M page to 4K page.
> + */
> + pte_base = (pte_t *)alloc_low_page(&pte_phys);
> + BUG_ON(!pte_base);
> + __split_large_page((pte_t *)pmd, addr,
> + (pte_t *)pte_base);
> +
> + spin_lock(&init_mm.page_table_lock);
> + pmd_populate_kernel(&init_mm, pmd, __va(pte_phys));
> + spin_unlock(&init_mm.page_table_lock);
> +
> + flush_tlb_all();
> + }
> +
> + pte_base = (pte_t *)map_low_page((pte_t *)pmd_page_vaddr(*pmd));
> + remove_pte_table(pte_base, addr, next, direct);
> + free_pte_table(pte_base, pmd);
> + unmap_low_page(pte_base);
> + }
> +
> + /* Call free_pmd_table() in remove_pud_table(). */
> + if (direct)
> + update_page_count(PG_LEVEL_2M, -pages);
> +}
> +
> +static void __meminit
> +remove_pud_table(pud_t *pud_start, unsigned long addr, unsigned long end,
> + bool direct)
> +{
> + unsigned long pmd_phys, next, pages = 0;
> + 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 (IS_ALIGNED(addr, PUD_SIZE) &&
> + IS_ALIGNED(next, PUD_SIZE)) {
> + if (!direct) {
> + free_pagetable(pud_page(*pud),
> + get_order(PUD_SIZE));
> + pages++;
> + }
> +
> + spin_lock(&init_mm.page_table_lock);
> + pud_clear(pud);
> + spin_unlock(&init_mm.page_table_lock);
> + continue;
> + }
> +
> + /*
> + * We use 1G page, but we need to remove part of them,
> + * so split 1G page to 2M page.
> + */
> + pmd_base = (pmd_t *)alloc_low_page(&pmd_phys);
> + BUG_ON(!pmd_base);
> + __split_large_page((pte_t *)pud, addr,
> + (pte_t *)pmd_base);
> +
> + spin_lock(&init_mm.page_table_lock);
> + pud_populate(&init_mm, pud, __va(pmd_phys));
> + spin_unlock(&init_mm.page_table_lock);
> +
> + flush_tlb_all();
> + }
> +
> + pmd_base = (pmd_t *)map_low_page((pmd_t *)pud_page_vaddr(*pud));
> + remove_pmd_table(pmd_base, addr, next, direct);
> + free_pmd_table(pmd_base, pud);
> + unmap_low_page(pmd_base);
> + }
> +
> + if (direct)
> + update_page_count(PG_LEVEL_1G, -pages);
> +}
> +
> +/* start and end are both virtual address. */
> +static void __meminit
> +remove_pagetable(unsigned long start, unsigned long end, bool direct)
> +{
> + unsigned long next;
> + pgd_t *pgd;
> + pud_t *pud;
> + bool pgd_changed = false;
> +
> + for (; start < end; start = next) {
> + pgd = pgd_offset_k(start);
> + if (!pgd_present(*pgd))
> + continue;
> +
> + next = pgd_addr_end(start, end);
> +
> + pud = (pud_t *)map_low_page((pud_t *)pgd_page_vaddr(*pgd));
> + remove_pud_table(pud, start, next, direct);
> + if (free_pud_table(pud, pgd))
> + pgd_changed = true;
> + unmap_low_page(pud);
> + }
> +
> + if (pgd_changed)
> + sync_global_pgds(start, end - 1);
> +
> + flush_tlb_all();
> +}
> +
> #ifdef CONFIG_MEMORY_HOTREMOVE
> int __ref arch_remove_memory(u64 start, u64 size)
> {
> diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
> index a718e0d..7dcb6f9 100644
> --- a/arch/x86/mm/pageattr.c
> +++ b/arch/x86/mm/pageattr.c
> @@ -501,21 +501,13 @@ out_unlock:
> return do_split;
> }
>
> -static int split_large_page(pte_t *kpte, unsigned long address)
> +int __split_large_page(pte_t *kpte, unsigned long address, pte_t *pbase)
> {
> unsigned long pfn, pfninc = 1;
> unsigned int i, level;
> - pte_t *pbase, *tmp;
> + pte_t *tmp;
> pgprot_t ref_prot;
> - struct page *base;
> -
> - if (!debug_pagealloc)
> - spin_unlock(&cpa_lock);
> - base = alloc_pages(GFP_KERNEL | __GFP_NOTRACK, 0);
> - if (!debug_pagealloc)
> - spin_lock(&cpa_lock);
> - if (!base)
> - return -ENOMEM;
> + struct page *base = virt_to_page(pbase);
>
> spin_lock(&pgd_lock);
> /*
> @@ -523,10 +515,11 @@ static int split_large_page(pte_t *kpte, unsigned long address)
> * up for us already:
> */
> tmp = lookup_address(address, &level);
> - if (tmp != kpte)
> - goto out_unlock;
> + if (tmp != kpte) {
> + spin_unlock(&pgd_lock);
> + return 1;
> + }
>
> - pbase = (pte_t *)page_address(base);
> paravirt_alloc_pte(&init_mm, page_to_pfn(base));
> ref_prot = pte_pgprot(pte_clrhuge(*kpte));
> /*
> @@ -579,17 +572,27 @@ static int split_large_page(pte_t *kpte, unsigned long address)
> * going on.
> */
> __flush_tlb_all();
> + spin_unlock(&pgd_lock);
>
> - base = NULL;
> + return 0;
> +}
>
> -out_unlock:
> - /*
> - * If we dropped out via the lookup_address check under
> - * pgd_lock then stick the page back into the pool:
> - */
> - if (base)
> +static int split_large_page(pte_t *kpte, unsigned long address)
> +{
> + pte_t *pbase;
> + struct page *base;
> +
> + if (!debug_pagealloc)
> + spin_unlock(&cpa_lock);
> + base = alloc_pages(GFP_KERNEL | __GFP_NOTRACK, 0);
> + if (!debug_pagealloc)
> + spin_lock(&cpa_lock);
> + if (!base)
> + return -ENOMEM;
> +
> + pbase = (pte_t *)page_address(base);
> + if (__split_large_page(kpte, address, pbase))
> __free_page(base);
> - spin_unlock(&pgd_lock);
>
> return 0;
> }
> diff --git a/include/linux/bootmem.h b/include/linux/bootmem.h
> index 3f778c2..190ff06 100644
> --- a/include/linux/bootmem.h
> +++ b/include/linux/bootmem.h
> @@ -53,6 +53,7 @@ extern void free_bootmem_node(pg_data_t *pgdat,
> unsigned long size);
> extern void free_bootmem(unsigned long physaddr, unsigned long size);
> extern void free_bootmem_late(unsigned long physaddr, unsigned long size);
> +extern void __free_pages_bootmem(struct page *page, unsigned int order);
>
> /*
> * Flags for reserve_bootmem (also if CONFIG_HAVE_ARCH_BOOTMEM_NODE,





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