Subject: Re: [PATCH v3 08/12] memory-hotplug: remove memmap of sparse-vmemmap

From: Jianguo Wu <[email-masked]>
Date: Tue, 27 Nov 2012 15:14:11 +0800

On 2012/11/27 14:49, Wen Congyang wrote:

> At 11/27/2012 01:47 PM, Jianguo Wu Wrote:
>> On 2012/11/1 17:44, Wen Congyang wrote:
>>
>>> From: Yasuaki Ishimatsu <[email-masked]>
>>>
>>> All pages of virtual mapping in removed memory cannot be freed, since some pages
>>> used as PGD/PUD includes not only removed memory but also other memory. So the
>>> patch checks whether page can be freed or not.
>>>
>>> How 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.
>>>
>>> Applying patch, __remove_section() of CONFIG_SPARSEMEM_VMEMMAP is integrated
>>> into one. So __remove_section() of CONFIG_SPARSEMEM_VMEMMAP is deleted.
>>>
>>> Note:  vmemmap_kfree() and vmemmap_free_bootmem() are not implemented for ia64,
>>> ppc, s390, and sparc.
>>>
>>> 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: Wen Congyang <[email-masked]>
>>> Signed-off-by: Yasuaki Ishimatsu <[email-masked]>
>>> ---
>>>  arch/ia64/mm/discontig.c  |   8 ++++
>>>  arch/powerpc/mm/init_64.c |   8 ++++
>>>  arch/s390/mm/vmem.c       |   8 ++++
>>>  arch/sparc/mm/init_64.c   |   8 ++++
>>>  arch/x86/mm/init_64.c     | 119 ++++++++++++++++++++++++++++++++++++++++++++++
>>>  include/linux/mm.h        |   2 +
>>>  mm/memory_hotplug.c       |  17 +------
>>>  mm/sparse.c               |   5 +-
>>>  8 files changed, 158 insertions(+), 17 deletions(-)
>>>
>>> diff --git a/arch/ia64/mm/discontig.c b/arch/ia64/mm/discontig.c
>>> index 33943db..0d23b69 100644
>>> --- a/arch/ia64/mm/discontig.c
>>> +++ b/arch/ia64/mm/discontig.c
>>> @@ -823,6 +823,14 @@ int __meminit vmemmap_populate(struct page *start_page,
>>>  	return vmemmap_populate_basepages(start_page, size, node);
>>>  }
>>>  
>>> +void vmemmap_kfree(struct page *memmap, unsigned long nr_pages)
>>> +{
>>> +}
>>> +
>>> +void vmemmap_free_bootmem(struct page *memmap, unsigned long nr_pages)
>>> +{
>>> +}
>>> +
>>>  void register_page_bootmem_memmap(unsigned long section_nr,
>>>  				  struct page *start_page, unsigned long size)
>>>  {
>>> diff --git a/arch/powerpc/mm/init_64.c b/arch/powerpc/mm/init_64.c
>>> index 6466440..df7d155 100644
>>> --- a/arch/powerpc/mm/init_64.c
>>> +++ b/arch/powerpc/mm/init_64.c
>>> @@ -298,6 +298,14 @@ int __meminit vmemmap_populate(struct page *start_page,
>>>  	return 0;
>>>  }
>>>  
>>> +void vmemmap_kfree(struct page *memmap, unsigned long nr_pages)
>>> +{
>>> +}
>>> +
>>> +void vmemmap_free_bootmem(struct page *memmap, unsigned long nr_pages)
>>> +{
>>> +}
>>> +
>>>  void register_page_bootmem_memmap(unsigned long section_nr,
>>>  				  struct page *start_page, unsigned long size)
>>>  {
>>> diff --git a/arch/s390/mm/vmem.c b/arch/s390/mm/vmem.c
>>> index 4f4803a..ab69c34 100644
>>> --- a/arch/s390/mm/vmem.c
>>> +++ b/arch/s390/mm/vmem.c
>>> @@ -236,6 +236,14 @@ out:
>>>  	return ret;
>>>  }
>>>  
>>> +void vmemmap_kfree(struct page *memmap, unsigned long nr_pages)
>>> +{
>>> +}
>>> +
>>> +void vmemmap_free_bootmem(struct page *memmap, unsigned long nr_pages)
>>> +{
>>> +}
>>> +
>>>  void register_page_bootmem_memmap(unsigned long section_nr,
>>>  				  struct page *start_page, unsigned long size)
>>>  {
>>> diff --git a/arch/sparc/mm/init_64.c b/arch/sparc/mm/init_64.c
>>> index 75a984b..546855d 100644
>>> --- a/arch/sparc/mm/init_64.c
>>> +++ b/arch/sparc/mm/init_64.c
>>> @@ -2232,6 +2232,14 @@ void __meminit vmemmap_populate_print_last(void)
>>>  	}
>>>  }
>>>  
>>> +void vmemmap_kfree(struct page *memmap, unsigned long nr_pages)
>>> +{
>>> +}
>>> +
>>> +void vmemmap_free_bootmem(struct page *memmap, unsigned long nr_pages)
>>> +{
>>> +}
>>> +
>>>  void register_page_bootmem_memmap(unsigned long section_nr,
>>>  				  struct page *start_page, unsigned long size)
>>>  {
>>> diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
>>> index 795dae3..e85626d 100644
>>> --- a/arch/x86/mm/init_64.c
>>> +++ b/arch/x86/mm/init_64.c
>>> @@ -998,6 +998,125 @@ vmemmap_populate(struct page *start_page, unsigned long size, int node)
>>>  	return 0;
>>>  }
>>>  
>>> +#define PAGE_INUSE 0xFD
>>> +
>>> +unsigned long find_and_clear_pte_page(unsigned long addr, unsigned long end,
>>> +			    struct page **pp, int *page_size)
>>> +{
>>> +	pgd_t *pgd;
>>> +	pud_t *pud;
>>> +	pmd_t *pmd;
>>> +	pte_t *pte = NULL;
>>> +	void *page_addr;
>>> +	unsigned long next;
>>> +
>>> +	*pp = NULL;
>>> +
>>> +	pgd = pgd_offset_k(addr);
>>> +	if (pgd_none(*pgd))
>>> +		return pgd_addr_end(addr, end);
>>> +
>>> +	pud = pud_offset(pgd, addr);
>>> +	if (pud_none(*pud))
>>> +		return pud_addr_end(addr, end);
>>> +
>>> +	if (!cpu_has_pse) {
>>> +		next = (addr + PAGE_SIZE) & PAGE_MASK;
>>> +		pmd = pmd_offset(pud, addr);
>>> +		if (pmd_none(*pmd))
>>> +			return next;
>>> +
>>> +		pte = pte_offset_kernel(pmd, addr);
>>> +		if (pte_none(*pte))
>>> +			return next;
>>> +
>>> +		*page_size = PAGE_SIZE;
>>> +		*pp = pte_page(*pte);
>>> +	} else {
>>> +		next = pmd_addr_end(addr, end);
>>> +
>>> +		pmd = pmd_offset(pud, addr);
>>> +		if (pmd_none(*pmd))
>>> +			return next;
>>> +
>>> +		*page_size = PMD_SIZE;
>>> +		*pp = pmd_page(*pmd);
>>> +	}
>>> +
>>> +	/*
>>> +	 * Removed page structs are filled with 0xFD.
>>> +	 */
>>> +	memset((void *)addr, PAGE_INUSE, next - addr);
>>> +
>>> +	page_addr = page_address(*pp);
>>> +
>>> +	/*
>>> +	 * Check the page is filled with 0xFD or not.
>>> +	 * memchr_inv() returns the address. In this case, we cannot
>>> +	 * clear PTE/PUD entry, since the page is used by other.
>>> +	 * So we cannot also free the page.
>>> +	 *
>>> +	 * memchr_inv() returns NULL. In this case, we can clear
>>> +	 * PTE/PUD entry, since the page is not used by other.
>>> +	 * So we can also free the page.
>>> +	 */
>>> +	if (memchr_inv(page_addr, PAGE_INUSE, *page_size)) {
>>> +		*pp = NULL;
>>> +		return next;
>>> +	}
>>> +
>>> +	if (!cpu_has_pse)
>>> +		pte_clear(&init_mm, addr, pte);
>>> +	else
>>> +		pmd_clear(pmd);
>>> +
>>> +	return next;
>>> +}
>>> +
>>> +void vmemmap_kfree(struct page *memmap, unsigned long nr_pages)
>>> +{
>>> +	unsigned long addr = (unsigned long)memmap;
>>> +	unsigned long end = (unsigned long)(memmap + nr_pages);
>>> +	unsigned long next;
>>> +	struct page *page;
>>> +	int page_size;
>>> +
>>> +	for (; addr < end; addr = next) {
>>> +		page = NULL;
>>> +		page_size = 0;
>>> +		next = find_and_clear_pte_page(addr, end, &page, &page_size);
>>> +		if (!page)
>>> +			continue;
>>> +
>>> +		free_pages((unsigned long)page_address(page),
>>> +			    get_order(page_size));
>>> +		__flush_tlb_one(addr);
>>> +	}
>>> +}
>>> +
>>> +void vmemmap_free_bootmem(struct page *memmap, unsigned long nr_pages)
>>> +{
>>> +	unsigned long addr = (unsigned long)memmap;
>>> +	unsigned long end = (unsigned long)(memmap + nr_pages);
>>> +	unsigned long next;
>>> +	struct page *page;
>>> +	int page_size;
>>> +	unsigned long magic;
>>> +
>>> +	for (; addr < end; addr = next) {
>>> +		page = NULL;
>>> +		page_size = 0;
>>> +		next = find_and_clear_pte_page(addr, end, &page, &page_size);
>>> +		if (!page)
>>> +			continue;
>>> +
>>> +		magic = (unsigned long) page->lru.next;
>>> +		if (magic == SECTION_INFO)
>>> +			put_page_bootmem(page);
>>> +		flush_tlb_kernel_range(addr, end);
>>> +	}
>>> +}
>>> +
>>>  void register_page_bootmem_memmap(unsigned long section_nr,
>>>  				  struct page *start_page, unsigned long size)
>>>  {
>>> diff --git a/include/linux/mm.h b/include/linux/mm.h
>>> index 8e5a56f..42b8723 100644
>>> --- a/include/linux/mm.h
>>> +++ b/include/linux/mm.h
>>> @@ -1642,6 +1642,8 @@ int vmemmap_populate(struct page *start_page, unsigned long pages, int node);
>>>  void vmemmap_populate_print_last(void);
>>>  void register_page_bootmem_memmap(unsigned long section_nr, struct page *map,
>>>  				  unsigned long size);
>>> +void vmemmap_kfree(struct page *memmpa, unsigned long nr_pages);
>>> +void vmemmap_free_bootmem(struct page *memmpa, unsigned long nr_pages);
>>>  
>>>  enum mf_flags {
>>>  	MF_COUNT_INCREASED = 1 << 0,
>>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>>> index db9806c..03153cf 100644
>>> --- a/mm/memory_hotplug.c
>>> +++ b/mm/memory_hotplug.c
>>> @@ -312,19 +312,6 @@ static int __meminit __add_section(int nid, struct zone *zone,
>>>  	return register_new_memory(nid, __pfn_to_section(phys_start_pfn));
>>>  }
>>>  
>>> -#ifdef CONFIG_SPARSEMEM_VMEMMAP
>>> -static int __remove_section(struct zone *zone, struct mem_section *ms)
>>> -{
>>> -	int ret = -EINVAL;
>>> -
>>> -	if (!valid_section(ms))
>>> -		return ret;
>>> -
>>> -	ret = unregister_memory_section(ms);
>>> -
>>> -	return ret;
>>> -}
>>> -#else
>>>  static int __remove_section(struct zone *zone, struct mem_section *ms)
>>>  {
>>>  	unsigned long flags;
>>> @@ -341,9 +328,9 @@ static int __remove_section(struct zone *zone, struct mem_section *ms)
>>>  	pgdat_resize_lock(pgdat, &flags);
>>>  	sparse_remove_one_section(zone, ms);
>>>  	pgdat_resize_unlock(pgdat, &flags);
>>> -	return 0;
>>> +
>>> +	return ret;
>>>  }
>>> -#endif
>>>  
>>>  /*
>>>   * Reasonably generic function for adding memory.  It is
>>> diff --git a/mm/sparse.c b/mm/sparse.c
>>> index fac95f2..ab9d755 100644
>>> --- a/mm/sparse.c
>>> +++ b/mm/sparse.c
>>> @@ -613,12 +613,13 @@ static inline struct page *kmalloc_section_memmap(unsigned long pnum, int nid,
>>>  	/* This will make the necessary allocations eventually. */
>>>  	return sparse_mem_map_populate(pnum, nid);
>>>  }
>>> -static void __kfree_section_memmap(struct page *memmap, unsigned long nr_pages)
>>> +static void __kfree_section_memmap(struct page *page, unsigned long nr_pages)
>>>  {
>>> -	return; /* XXX: Not implemented yet */
>>> +	vmemmap_kfree(page, nr_pages);
>>>  }
>>>  static void free_map_bootmem(struct page *page, unsigned long nr_pages)
>>>  {
>>> +	vmemmap_free_bootmem(page, nr_pages);
>>>  }
>>
>> Hi Congyang,
>> 	For vmemmap, nr_pages should be PAGES_PER_SECTION for free_map_bootmem(),
>> which is passed by free_section_usemap(), right? 
>> But now, nr_pages = PAGE_ALIGN(PAGES_PER_SECTION * sizeof(struct page)) >> PAGE_SHIFT.
>>
>> Signed-off-by: Jianguo Wu <[email-masked]>
>> ---
>>  mm/sparse.c |    4 ++++
>>  1 files changed, 4 insertions(+), 0 deletions(-)
>>
>> diff --git a/mm/sparse.c b/mm/sparse.c
>> index fac95f2..31e5282 100644
>> --- a/mm/sparse.c
>> +++ b/mm/sparse.c
>> @@ -713,8 +713,12 @@ static void free_section_usemap(struct page *memmap, unsigned long *usemap)
>>  		struct page *memmap_page;
>>  		memmap_page = virt_to_page(memmap);
>>  
>> +#ifdef CONFIG_SPARSEMEM_VMEMMAP
>> +		nr_pages = PAGES_PER_SECTION;
>> +#else
>>  		nr_pages = PAGE_ALIGN(PAGES_PER_SECTION * sizeof(struct page))
>>  			>> PAGE_SHIFT;
>> +#endif
> 
> Hmm, to avoid using ifdef, I think we can pass PAGE_PER_SECTION to free_map_bootmem(),
> and calculate how many pages is used to store struct page.
> 

yes, it is ugly to use ifdef. Or we can remove parameter--nr_pages of free_map_bootmem(),
and calculate nr_pages in free_map_bootmem() directly.

> Thanks
> Wen Congyang
> 
>>  
>>  		free_map_bootmem(memmap_page, nr_pages);
>>  	}
> 
> 
> .
>