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

From: Yasuaki Ishimatsu <[email-masked]>
Date: Wed, 11 Jul 2012 14:52:48 +0900

2012/07/11 14:06, Wen Congyang wrote:
Hi Wen,

> 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 <[email-masked]>
>> CC: Jiang Liu <[email-masked]>
>> CC: Len Brown <[email-masked]>
>> CC: Benjamin Herrenschmidt <[email-masked]>
>> CC: Paul Mackerras <[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/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().

Yes.

> 
>>   }
>>   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?

The function try to free memory allocated from bootmem. The memory has
been registered by get_page_bootmem(). So we can free the memory by
put_page_bootmem().

> 
>>   #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?

Does it mean "return (addr + PGDIR_SIZE) & PGDIR_MASK"?

> 
>> +
>> +	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.

Thanks, I'll update it.

> 
>> +	} 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.

Does it mean the if sentence is unnecessary?

> 
>> +		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.

The memory has page structures for hot-removed memory. So nobody is using
these pages, since the hot-removed memory has been offlined.

>> +		}
>> +	}
>> +}
>> +
>> +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.

I'll update it.

Thanks,
Yasuaki Ishimatsu

> 
> 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
>>
>>
>