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

From: Jianguo Wu <[email-masked]>
Date: Wed, 30 Jan 2013 09:53:13 +0800

On 2013/1/29 21:02, Simon Jeons wrote:

> 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?

Hi Simon,

For x86_64, page table of hot-add memory is created by:
    add_memory->arch_add_memory->init_memory_mapping->kernel_physical_mapping_init

> 
>> 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,
> 
> 
> 
> .
>