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

From: Wen Congyang <[email-masked]>
Date: Tue, 27 Nov 2012 14:39:55 +0800

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? 

Yes, you are right. I will merge it into my patchset.

I will sent the new patchset later today.

Thanks
Wen Congyang

> 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
>  
>  		free_map_bootmem(memmap_page, nr_pages);
>  	}