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

From: Wen Congyang <[email-masked]>
Date: Tue, 23 Oct 2012 15:41:38 +0800

At 10/23/2012 03:09 PM, wujianguo Wrote:
> On 2012-10-22 15:11, Wen Congyang wrote:
>> 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?
> Sorry, I made a mistake here. Only if the page was allocated at booting, we should update
> zone and totalram_pages(zone->present_pages and totalram_pages mean pages which are
> managed by buddy system).
> 
> How about:
> static inline void free_pagetable(struct page *page)
> {
> 	struct zone *zone;
> 	bool bootmem = false;
> 
> 	/* bootmem page has reserved flag */
> 	if (PageReserved(page)) {
> 		__ClearPageReserved(page);
> 		bootmem = true;
> 	}
> 
> 	__free_page(page);
> 	
> 	if (bootmem) {
> 		zone = page_zone(page);
> 		zone_span_writelock(zone);
> 		zone->present_pages++;
> 		zone_span_writeunlock(zone);
> 		totalram_pages++;
> 	}
> }

This verson looks fine to me.

> 
>>
>>> +}
>>> +
>>> +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.
> The page is only used by page table, so is safe to free it when all the page table
> entries have been cleared, right?

Yes, but I guess we need to do more. For example, all boot memory are in memblock.reserved,
and you don't update memblock here.

Thanks
Wen Congyang

> 
>>
>>> +		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?
>>
> Yes, sure.
> 
> Thanks,
> Jianguo Wu
> 
>> 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>
>>>>
>>>
>>>
>>
>>
> 
>