Subject: Re: [PATCH 8/10] memory-hotplug : remove page table of x86_64 architecture

From: Wen Congyang <[email-masked]>
Date: Mon, 22 Oct 2012 15:11:17 +0800

Hi, Wu

Sorry for late reply.

At 10/09/2012 04:26 PM, wujianguo Wrote:
> Hi Congyang,
> 	I think we should also free pages which are used by page tables after removing
> page tables of the memory.

It is OK to do it.

> 
> From: Jianguo Wu <[email-masked]>
> 
> Signed-off-by: Jianguo Wu <[email-masked]>
> Signed-off-by: Jiang Liu <[email-masked]>
> ---
>  arch/x86/mm/init_64.c |  110 +++++++++++++++++++++++++++++++++++++++---------
>  1 files changed, 89 insertions(+), 21 deletions(-)
> 
> diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
> index 5596dfa..81f9c3b 100644
> --- a/arch/x86/mm/init_64.c
> +++ b/arch/x86/mm/init_64.c
> @@ -675,6 +675,74 @@ int arch_add_memory(int nid, u64 start, u64 size)
>  }
>  EXPORT_SYMBOL_GPL(arch_add_memory);
> 
> +static inline void free_pagetable(struct page *page)
> +{
> +	struct zone *zone;
> +
> +	__ClearPageReserved(page);
> +	__free_page(page);
> +
> +	zone = page_zone(page);
> +	zone_span_writelock(zone);
> +	zone->present_pages++;
> +	zone_span_writeunlock(zone);
> +	totalram_pages++;

Why do you update zone and totalram_pages here?

> +}
> +
> +static void 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))
> +			break;
> +	}
> +
> +	/* free a pte talbe */
> +	if (i == PTRS_PER_PTE) {
> +		free_pagetable(pmd_page(*pmd));

The memory may be allocated at booting. So it is very dangerous to
free it without any check.

> +		pmd_clear(pmd);
> +	}
> +}
> +
> +static void 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))
> +			break;
> +	}
> +
> +	/* free a pmd talbe */
> +	if (i == PTRS_PER_PMD) {
> +		free_pagetable(pud_page(*pud));
> +		pud_clear(pud);
> +	}
> +}
> +
> +static void 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))
> +			break;
> +	}
> +
> +	/* free a pud table */
> +	if (i == PTRS_PER_PUD) {
> +		free_pagetable(pgd_page(*pgd));
> +		pgd_clear(pgd);
> +	}
> +}
> +
>  static void __meminit
>  phys_pte_remove(pte_t *pte_page, unsigned long addr, unsigned long end)
>  {
> @@ -704,21 +772,19 @@ phys_pmd_remove(pmd_t *pmd_page, unsigned long addr, unsigned long end)
>  	unsigned long pages = 0, next;
>  	int i = pmd_index(addr);
> 
> -	for (; i < PTRS_PER_PMD; i++, addr = next) {
> +	for (; i < PTRS_PER_PMD && addr < end; i++, addr = next) {
>  		unsigned long pte_phys;
>  		pmd_t *pmd = pmd_page + pmd_index(addr);
>  		pte_t *pte;
> 
> -		if (addr >= end)
> -			break;
> -
> -		next = (addr & PMD_MASK) + PMD_SIZE;
> +		next = pmd_addr_end(addr, end);
> 
>  		if (!pmd_present(*pmd))
>  			continue;
> 
>  		if (pmd_large(*pmd)) {
> -			if ((addr & ~PMD_MASK) == 0 && next <= end) {
> +			if (IS_ALIGNED(addr, PMD_SIZE) &&
> +			    IS_ALIGNED(next, PMD_SIZE)) {
>  				set_pmd(pmd, __pmd(0));
>  				pages++;
>  				continue;
> @@ -729,7 +795,8 @@ phys_pmd_remove(pmd_t *pmd_page, unsigned long addr, unsigned long end)
>  			 * so split 2M page to 4K page.
>  			 */
>  			pte = alloc_low_page(&pte_phys);
> -			__split_large_page((pte_t *)pmd, addr, pte);
> +			__split_large_page((pte_t *)pmd,
> +					   (unsigned long)__va(addr), pte);
> 
>  			spin_lock(&init_mm.page_table_lock);
>  			pmd_populate_kernel(&init_mm, pmd, __va(pte_phys));
> @@ -738,7 +805,8 @@ phys_pmd_remove(pmd_t *pmd_page, unsigned long addr, unsigned long end)
> 
>  		spin_lock(&init_mm.page_table_lock);
>  		pte = map_low_page((pte_t *)pmd_page_vaddr(*pmd));
> -		phys_pte_remove(pte, addr, end);
> +		phys_pte_remove(pte, addr, next);
> +		free_pte_table(pte, pmd);
>  		unmap_low_page(pte);
>  		spin_unlock(&init_mm.page_table_lock);
>  	}
> @@ -751,21 +819,19 @@ phys_pud_remove(pud_t *pud_page, unsigned long addr, unsigned long end)
>  	unsigned long pages = 0, next;
>  	int i = pud_index(addr);
> 
> -	for (; i < PTRS_PER_PUD; i++, addr = next) {
> +	for (; i < PTRS_PER_PUD && addr < end; i++, addr = next) {
>  		unsigned long pmd_phys;
>  		pud_t *pud = pud_page + pud_index(addr);
>  		pmd_t *pmd;
> 
> -		if (addr >= end)
> -			break;
> -
> -		next = (addr & PUD_MASK) + PUD_SIZE;
> +		next = pud_addr_end(addr, end);
> 
>  		if (!pud_present(*pud))
>  			continue;
> 
>  		if (pud_large(*pud)) {
> -			if ((addr & ~PUD_MASK) == 0 && next <= end) {
> +			if (IS_ALIGNED(addr, PUD_SIZE) &&
> +			    IS_ALIGNED(next, PUD_SIZE)) {
>  				set_pud(pud, __pud(0));
>  				pages++;
>  				continue;
> @@ -776,15 +842,18 @@ phys_pud_remove(pud_t *pud_page, unsigned long addr, unsigned long end)
>  			 * so split 1G page to 2M page.
>  			 */
>  			pmd = alloc_low_page(&pmd_phys);
> -			__split_large_page((pte_t *)pud, addr, (pte_t *)pmd);
> +			__split_large_page((pte_t *)pud,
> +					   (unsigned long)__va(addr),
> +					   (pte_t *)pmd);
> 
>  			spin_lock(&init_mm.page_table_lock);
>  			pud_populate(&init_mm, pud, __va(pmd_phys));
>  			spin_unlock(&init_mm.page_table_lock);
>  		}
> 
> -		pmd = map_low_page(pmd_offset(pud, 0));
> -		phys_pmd_remove(pmd, addr, end);
> +		pmd = map_low_page((pmd_t *)pud_page_vaddr(*pud));

Hmm, pmd_offset(pud, 0) is equal to (pmd_t *)pud_page_vaddr(*pud).

Is it OK to merge your patch into my patch?

Thanks
Wen Congyang

> +		phys_pmd_remove(pmd, addr, next);
> +		free_pmd_table(pmd, pud);
>  		unmap_low_page(pmd);
>  		__flush_tlb_all();
>  	}
> @@ -805,15 +874,14 @@ kernel_physical_mapping_remove(unsigned long start, unsigned long end)
>  		pgd_t *pgd = pgd_offset_k(start);
>  		pud_t *pud;
> 
> -		next = (start + PGDIR_SIZE) & PGDIR_MASK;
> -		if (next > end)
> -			next = end;
> +		next = pgd_addr_end(start, end);
> 
>  		if (!pgd_present(*pgd))
>  			continue;
> 
>  		pud = map_low_page((pud_t *)pgd_page_vaddr(*pgd));
> -		phys_pud_remove(pud, __pa(start), __pa(end));
> +		phys_pud_remove(pud, __pa(start), __pa(next));
> +		free_pud_table(pud, pgd);
>  		unmap_low_page(pud);
>  	}
> 
> -- 1.7.6.1 .
> 
> 
> On 2012-10-5 10:36, Yasuaki Ishimatsu wrote:
>> From: Wen Congyang <[email-masked]>
>>
>> For hot removing memory, we sholud remove page table about the memory.
>> So the patch searches a page table about the removed memory, and clear
>> page table.
>>
>> CC: David Rientjes <[email-masked]>
>> CC: Jiang Liu <[email-masked]>
>> CC: Len Brown <[email-masked]>
>> CC: Christoph Lameter <[email-masked]>
>> Cc: Minchan Kim <[email-masked]>
>> CC: Andrew Morton <[email-masked]>
>> CC: KOSAKI Motohiro <[email-masked]>
>> CC: Yasuaki Ishimatsu <[email-masked]>
>> Signed-off-by: Wen Congyang <[email-masked]>
>> ---
>>  arch/x86/include/asm/pgtable_types.h |    1 
>>  arch/x86/mm/init_64.c                |  147 +++++++++++++++++++++++++++++++++++
>>  arch/x86/mm/pageattr.c               |   47 +++++------
>>  3 files changed, 173 insertions(+), 22 deletions(-)
>>
>> Index: linux-3.6/arch/x86/mm/init_64.c
>> ===================================================================
>> --- linux-3.6.orig/arch/x86/mm/init_64.c	2012-10-04 18:30:21.171698416 +0900
>> +++ linux-3.6/arch/x86/mm/init_64.c	2012-10-04 18:30:27.317704652 +0900
>> @@ -675,6 +675,151 @@ int arch_add_memory(int nid, u64 start, 
>>  }
>>  EXPORT_SYMBOL_GPL(arch_add_memory);
>>  
>> +static void __meminit
>> +phys_pte_remove(pte_t *pte_page, unsigned long addr, unsigned long end)
>> +{
>> +	unsigned pages = 0;
>> +	int i = pte_index(addr);
>> +
>> +	pte_t *pte = pte_page + pte_index(addr);
>> +
>> +	for (; i < PTRS_PER_PTE; i++, addr += PAGE_SIZE, pte++) {
>> +
>> +		if (addr >= end)
>> +			break;
>> +
>> +		if (!pte_present(*pte))
>> +			continue;
>> +
>> +		pages++;
>> +		set_pte(pte, __pte(0));
>> +	}
>> +
>> +	update_page_count(PG_LEVEL_4K, -pages);
>> +}
>> +
>> +static void __meminit
>> +phys_pmd_remove(pmd_t *pmd_page, unsigned long addr, unsigned long end)
>> +{
>> +	unsigned long pages = 0, next;
>> +	int i = pmd_index(addr);
>> +
>> +	for (; i < PTRS_PER_PMD; i++, addr = next) {
>> +		unsigned long pte_phys;
>> +		pmd_t *pmd = pmd_page + pmd_index(addr);
>> +		pte_t *pte;
>> +
>> +		if (addr >= end)
>> +			break;
>> +
>> +		next = (addr & PMD_MASK) + PMD_SIZE;
>> +
>> +		if (!pmd_present(*pmd))
>> +			continue;
>> +
>> +		if (pmd_large(*pmd)) {
>> +			if ((addr & ~PMD_MASK) == 0 && next <= end) {
>> +				set_pmd(pmd, __pmd(0));
>> +				pages++;
>> +				continue;
>> +			}
>> +
>> +			/*
>> +			 * We use 2M page, but we need to remove part of them,
>> +			 * so split 2M page to 4K page.
>> +			 */
>> +			pte = alloc_low_page(&pte_phys);
>> +			__split_large_page((pte_t *)pmd, addr, pte);
>> +
>> +			spin_lock(&init_mm.page_table_lock);
>> +			pmd_populate_kernel(&init_mm, pmd, __va(pte_phys));
>> +			spin_unlock(&init_mm.page_table_lock);
>> +		}
>> +
>> +		spin_lock(&init_mm.page_table_lock);
>> +		pte = map_low_page((pte_t *)pmd_page_vaddr(*pmd));
>> +		phys_pte_remove(pte, addr, end);
>> +		unmap_low_page(pte);
>> +		spin_unlock(&init_mm.page_table_lock);
>> +	}
>> +	update_page_count(PG_LEVEL_2M, -pages);
>> +}
>> +
>> +static void __meminit
>> +phys_pud_remove(pud_t *pud_page, unsigned long addr, unsigned long end)
>> +{
>> +	unsigned long pages = 0, next;
>> +	int i = pud_index(addr);
>> +
>> +	for (; i < PTRS_PER_PUD; i++, addr = next) {
>> +		unsigned long pmd_phys;
>> +		pud_t *pud = pud_page + pud_index(addr);
>> +		pmd_t *pmd;
>> +
>> +		if (addr >= end)
>> +			break;
>> +
>> +		next = (addr & PUD_MASK) + PUD_SIZE;
>> +
>> +		if (!pud_present(*pud))
>> +			continue;
>> +
>> +		if (pud_large(*pud)) {
>> +			if ((addr & ~PUD_MASK) == 0 && next <= end) {
>> +				set_pud(pud, __pud(0));
>> +				pages++;
>> +				continue;
>> +			}
>> +
>> +			/*
>> +			 * We use 1G page, but we need to remove part of them,
>> +			 * so split 1G page to 2M page.
>> +			 */
>> +			pmd = alloc_low_page(&pmd_phys);
>> +			__split_large_page((pte_t *)pud, addr, (pte_t *)pmd);
>> +
>> +			spin_lock(&init_mm.page_table_lock);
>> +			pud_populate(&init_mm, pud, __va(pmd_phys));
>> +			spin_unlock(&init_mm.page_table_lock);
>> +		}
>> +
>> +		pmd = map_low_page(pmd_offset(pud, 0));
>> +		phys_pmd_remove(pmd, addr, end);
>> +		unmap_low_page(pmd);
>> +		__flush_tlb_all();
>> +	}
>> +	__flush_tlb_all();
>> +
>> +	update_page_count(PG_LEVEL_1G, -pages);
>> +}
>> +
>> +void __meminit
>> +kernel_physical_mapping_remove(unsigned long start, unsigned long end)
>> +{
>> +	unsigned long next;
>> +
>> +	start = (unsigned long)__va(start);
>> +	end = (unsigned long)__va(end);
>> +
>> +	for (; start < end; start = next) {
>> +		pgd_t *pgd = pgd_offset_k(start);
>> +		pud_t *pud;
>> +
>> +		next = (start + PGDIR_SIZE) & PGDIR_MASK;
>> +		if (next > end)
>> +			next = end;
>> +
>> +		if (!pgd_present(*pgd))
>> +			continue;
>> +
>> +		pud = map_low_page((pud_t *)pgd_page_vaddr(*pgd));
>> +		phys_pud_remove(pud, __pa(start), __pa(end));
>> +		unmap_low_page(pud);
>> +	}
>> +
>> +	__flush_tlb_all();
>> +}
>> +
>>  #ifdef CONFIG_MEMORY_HOTREMOVE
>>  int __ref arch_remove_memory(u64 start, u64 size)
>>  {
>> @@ -687,6 +832,8 @@ int __ref arch_remove_memory(u64 start, 
>>  	ret = __remove_pages(zone, start_pfn, nr_pages);
>>  	WARN_ON_ONCE(ret);
>>  
>> +	kernel_physical_mapping_remove(start, start + size);
>> +
>>  	return ret;
>>  }
>>  #endif
>> Index: linux-3.6/arch/x86/include/asm/pgtable_types.h
>> ===================================================================
>> --- linux-3.6.orig/arch/x86/include/asm/pgtable_types.h	2012-10-04 18:26:51.925486954 +0900
>> +++ linux-3.6/arch/x86/include/asm/pgtable_types.h	2012-10-04 18:30:27.322704656 +0900
>> @@ -334,6 +334,7 @@ static inline void update_page_count(int
>>   * 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__ */
>>  
>> Index: linux-3.6/arch/x86/mm/pageattr.c
>> ===================================================================
>> --- linux-3.6.orig/arch/x86/mm/pageattr.c	2012-10-04 18:26:51.923486952 +0900
>> +++ linux-3.6/arch/x86/mm/pageattr.c	2012-10-04 18:30:27.328704662 +0900
>> @@ -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,
>>  	 * 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,
>>  	 * 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;
>>  }
>>
>> --
>> To unsubscribe, send a message with 'unsubscribe linux-mm' in
>> the body to [email-masked].  For more info on Linux MM,
>> see: http://www.linux-mm.org/ .
>> Don't email: <a href=mailto:"[email-masked]"> [email-masked] </a>
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> 
>