Re: [RFC PATCH v3 11/13] memory-hotplug : free memmap of sparse-vmemmap

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

At 07/09/2012 06:33 PM, Yasuaki Ishimatsu Wrote:
> I don't think that all pages of virtual mapping in removed memory can be
> freed, since page which type is MIX_SECTION_INFO is difficult to free.
> So, the patch only frees page which type is SECTION_INFO at first.
> 
> 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 |   91 ++++++++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/mm.h    |    2 +
>  mm/memory_hotplug.c   |    5 ++
>  mm/sparse.c           |    5 +-
>  4 files changed, 101 insertions(+), 2 deletions(-)
> 
> Index: linux-3.5-rc4/include/linux/mm.h
> ===================================================================
> --- linux-3.5-rc4.orig/include/linux/mm.h	2012-07-03 14:22:18.530011567 +0900
> +++ linux-3.5-rc4/include/linux/mm.h	2012-07-03 14:22:20.999983872 +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-rc4/mm/sparse.c
> ===================================================================
> --- linux-3.5-rc4.orig/mm/sparse.c	2012-07-03 14:21:45.071429805 +0900
> +++ linux-3.5-rc4/mm/sparse.c	2012-07-03 14:22:21.000983767 +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);

Hmm, I think you try to free the memory allocated in kmalloc_section_memmap().

>  }
>  static void free_map_bootmem(struct page *page, unsigned long nr_pages)
>  {
> +	vmemmap_free_bootmem(page, nr_pages);
>  }

Hmm, which function is the memory you try to free allocated in?

>  #else
>  static struct page *__kmalloc_section_memmap(unsigned long nr_pages)
> Index: linux-3.5-rc4/arch/x86/mm/init_64.c
> ===================================================================
> --- linux-3.5-rc4.orig/arch/x86/mm/init_64.c	2012-07-03 14:22:18.538011465 +0900
> +++ linux-3.5-rc4/arch/x86/mm/init_64.c	2012-07-03 14:22:21.007983103 +0900
> @@ -978,6 +978,97 @@ vmemmap_populate(struct page *start_page
>  	return 0;
>  }
> 
> +unsigned long find_and_clear_pte_page(unsigned long addr, unsigned long end,
> +				      struct page **pp)
> +{
> +	pgd_t *pgd;
> +	pud_t *pud;
> +	pmd_t *pmd;
> +	pte_t *pte;
> +	unsigned long next;
> +
> +	*pp = NULL;
> +
> +	pgd = pgd_offset_k(addr);
> +	if (pgd_none(*pgd))
> +		return (addr + PAGE_SIZE) & PAGE_MASK;

Hmm, why not goto next pgd?

> +
> +	pud = pud_offset(pgd, addr);
> +	if (pud_none(*pud))
> +		return (addr + PAGE_SIZE) & PAGE_MASK;
> +
> +	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;
> +
> +		*pp = pte_page(*pte);
> +		pte_clear(&init_mm, addr, pte);

I think you should flush tlb here.

> +	} else {
> +		next = pmd_addr_end(addr, end);
> +
> +		pmd = pmd_offset(pud, addr);
> +		if (pmd_none(*pmd))
> +			return next;
> +
> +		*pp = pmd_page(*pmd);
> +		pmd_clear(pmd);
> +	}
> +
> +	return next;
> +}
> +
> +void __meminit
> +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;
> +	unsigned int order;
> +	struct page *page;
> +
> +	for (; addr < end; addr = next) {
> +		page = NULL;
> +		next = find_and_clear_pte_page(addr, end, &page);
> +		if (!page)
> +			continue;
> +
> +		if (is_vmalloc_addr(page_address(page)))
> +			vfree(page_address(page));

Hmm, the memory is allocated in vmemmap_alloc_block(), and the address
can not be vmalloc address.

> +		else {
> +			order = next - addr;
> +			free_pages((unsigned long)page_address(page),
> +				   get_order(order));

OOPS. I think we cannot free pages here.

sizeof(struct page) is less than PAGE_SIZE. We store more than one struct
page in the same page. If you free it here while the other struct page
is in use, it is very dangerous.

> +		}
> +	}
> +}
> +
> +void __meminit
> +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;
> +	unsigned long magic;
> +
> +	for (; addr < end; addr = next) {
> +		page = NULL;
> +		next = find_and_clear_pte_page(addr, end, &page);
> +		if (!page)
> +			continue;
> +
> +		magic = (unsigned long) page->lru.next;
> +		if (magic == SECTION_INFO)
> +			put_page_bootmem(page);
> +	}
> +}
> +
>  void __meminit
>  register_page_bootmem_memmap(unsigned long section_nr, struct page *start_page,
>  			     unsigned long size)
> Index: linux-3.5-rc4/mm/memory_hotplug.c
> ===================================================================
> --- linux-3.5-rc4.orig/mm/memory_hotplug.c	2012-07-03 14:22:18.522011667 +0900
> +++ linux-3.5-rc4/mm/memory_hotplug.c	2012-07-03 14:22:21.012982694 +0900
> @@ -303,6 +303,8 @@ static int __meminit __add_section(int n
>  #ifdef CONFIG_SPARSEMEM_VMEMMAP

I think this line can be removed now.

Thanks
Wen Congyang

>  static int __remove_section(struct zone *zone, struct mem_section *ms)
>  {
> +	unsigned long flags;
> +	struct pglist_data *pgdat = zone->zone_pgdat;
>  	int ret;
> 
>  	if (!valid_section(ms))
> @@ -310,6 +312,9 @@ static int __remove_section(struct zone
> 
>  	ret = unregister_memory_section(ms);
> 
> +	pgdat_resize_lock(pgdat, &flags);
> +	sparse_remove_one_section(zone, ms);
> +	pgdat_resize_unlock(pgdat, &flags);
>  	return ret;
>  }
>  #else
> 
>