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

From: wujianguo <[email-masked]>
Date: Tue, 23 Oct 2012 15:09:11 +0800

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++;
	}
}

> 
>> +}
>> +
>> +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?

> 
>> +		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>
>>>
>>
>>
> 
>