Subject: Re: [PATCH v6 08/15] memory-hotplug: Common APIs to support page tables hot-remove

From: Simon Jeons <[email-masked]>
Date: Tue, 29 Jan 2013 07:02:24 -0600

Hi Tang,
On Wed, 2013-01-09 at 17:32 +0800, Tang Chen wrote:
> From: Wen Congyang <[email-masked]>
> 
> 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.
> 

When page table of hot-add memory is created?

> 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 <[email-masked]>
> Signed-off-by: Jianguo Wu <[email-masked]>
> Signed-off-by: Wen Congyang <[email-masked]>
> Signed-off-by: Tang Chen <[email-masked]>
> ---
>  arch/x86/include/asm/pgtable_types.h |    1 +
>  arch/x86/mm/init_64.c                |  299 ++++++++++++++++++++++++++++++++++
>  arch/x86/mm/pageattr.c               |   47 +++---
>  include/linux/bootmem.h              |    1 +
>  4 files changed, 326 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 9ac1723..fe01116 100644
> --- a/arch/x86/mm/init_64.c
> +++ b/arch/x86/mm/init_64.c
> @@ -682,6 +682,305 @@ 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;
> +	unsigned int nr_pages = 1 << order;
> +
> +	/* 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) {
> +			while (nr_pages--)
> +				put_page_bootmem(page++);
> +		} 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 += nr_pages;
> +		zone_span_writeunlock(zone);
> +		totalram_pages += nr_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,