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

[Wen Congyang <wency@cn.fujitsu.com>]

At 07/19/2012 05:45 PM, Wen Congyang Wrote:
> 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@google.com>
>> CC: Jiang Liu <liuj97@gmail.com>
>> CC: Len Brown <len.brown@intel.com>
>> CC: Benjamin Herrenschmidt <benh@kernel.crashing.org>
>> CC: Paul Mackerras <paulus@samba.org> 
>> CC: Christoph Lameter <cl@linux.com>
>> Cc: Minchan Kim <minchan.kim@gmail.com>
>> CC: Andrew Morton <akpm@linux-foundation.org>
>> CC: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> 
>> CC: Wen Congyang <wency@cn.fujitsu.com>
>> Signed-off-by: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
>>
>> ---
>>  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)?

I understand it now. page is for the memory to store struct page.

You clear page table's entry for the addr, not page_address(page).
And the entry for page_address(page) is still valid now.
So I think you want this:
__flush_tlb_one(addr);

Thanks
Wen Congyang

> 
> 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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