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

From: Jianguo Wu <[email-masked]>
Date: Tue, 27 Nov 2012 13:47:44 +0800

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
 
 		free_map_bootmem(memmap_page, nr_pages);
 	}
-- 
1.7.6.1

>  #else
>  static struct page *__kmalloc_section_memmap(unsigned long nr_pages)