Re: [RFC PATCH v4 11/13] memory-hotplug : free memmap of sparse-vmemmap

[Wen Congyang]

At 07/18/2012 06:16 PM, Yasuaki Ishimatsu Wrote:
> 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.
> 
> CC: David Rientjes <rientjes@xxxxxxxxxx>
> CC: Jiang Liu <liuj97@xxxxxxxxx>
> CC: Len Brown <len.brown@xxxxxxxxx>
> CC: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
> CC: Paul Mackerras <paulus@xxxxxxxxx> 
> CC: Christoph Lameter <cl@xxxxxxxxx>
> Cc: Minchan Kim <minchan.kim@xxxxxxxxx>
> CC: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> CC: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx> 
> CC: Wen Congyang <wency@xxxxxxxxxxxxxx>
> Signed-off-by: Yasuaki Ishimatsu <isimatu.yasuaki@xxxxxxxxxxxxxx>
> 
> ---
>  arch/x86/mm/init_64.c |  121 ++++++++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/mm.h    |    2 
>  mm/memory_hotplug.c   |   19 -------
>  mm/sparse.c           |    5 +-
>  4 files changed, 128 insertions(+), 19 deletions(-)
> 
> Index: linux-3.5-rc6/include/linux/mm.h
> ===================================================================
> --- linux-3.5-rc6.orig/include/linux/mm.h	2012-07-18 18:01:28.000000000 +0900
> +++ linux-3.5-rc6/include/linux/mm.h	2012-07-18 18:03:05.551168773 +0900
> @@ -1588,6 +1588,8 @@ int vmemmap_populate(struct page *start_
>  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,
> Index: linux-3.5-rc6/mm/sparse.c
> ===================================================================
> --- linux-3.5-rc6.orig/mm/sparse.c	2012-07-18 17:59:25.000000000 +0900
> +++ linux-3.5-rc6/mm/sparse.c	2012-07-18 18:03:05.553168749 +0900
> @@ -614,12 +614,13 @@ static inline struct page *kmalloc_secti
>  	/* 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);
>  }
>  #else
>  static struct page *__kmalloc_section_memmap(unsigned long nr_pages)
> Index: linux-3.5-rc6/arch/x86/mm/init_64.c
> ===================================================================
> --- linux-3.5-rc6.orig/arch/x86/mm/init_64.c	2012-07-18 18:01:28.000000000 +0900
> +++ linux-3.5-rc6/arch/x86/mm/init_64.c	2012-07-18 18:03:05.564168611 +0900
> @@ -978,6 +978,127 @@ vmemmap_populate(struct page *start_page
>  	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;
> +	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((unsigned long)page_address(page));

I think you want to free the memory to store struct page.
So why you free page_address(page)?

Thanks
Wen Congyang

> +	}
> +
> +}
> +
> +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)
>  {
> Index: linux-3.5-rc6/mm/memory_hotplug.c
> ===================================================================
> --- linux-3.5-rc6.orig/mm/memory_hotplug.c	2012-07-18 18:01:28.000000000 +0900
> +++ linux-3.5-rc6/mm/memory_hotplug.c	2012-07-18 18:25:11.036597977 +0900
> @@ -300,7 +300,6 @@ static int __meminit __add_section(int n
>  	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;
> @@ -309,29 +308,15 @@ static int __remove_section(struct zone 
>  		return ret;
>  
>  	ret = unregister_memory_section(ms);
> -
> -	return ret;
> -}
> -#else
> -static int __remove_section(struct zone *zone, struct mem_section *ms)
> -{
> -	unsigned long flags;
> -	struct pglist_data *pgdat = zone->zone_pgdat;
> -	int ret = -EINVAL;
> -
> -	if (!valid_section(ms))
> -		return ret;
> -
> -	ret = unregister_memory_section(ms);
>  	if (ret)
>  		return ret;
>  
>  	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
> 
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