Subject: Re: [RFC v9 PATCH 16/21] memory-hotplug: free memmap of sparse-vmemmap

From: Ni zhan Chen <[email-masked]>
Date: Sat, 06 Oct 2012 22:18:18 +0800

On 10/04/2012 02:26 PM, Yasuaki Ishimatsu wrote:
> Hi Chen,
>
> Sorry for late reply.
>
> 2012/10/02 13:21, Ni zhan Chen wrote:
>> On 09/05/2012 05:25 PM, [email-masked] 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: 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/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 3690c44..835a2b3 100644
>>> --- a/arch/powerpc/mm/init_64.c
>>> +++ b/arch/powerpc/mm/init_64.c
>>> @@ -299,6 +299,14 @@ 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 eda55cd..4b42b0b 100644
>>> --- a/arch/s390/mm/vmem.c
>>> +++ b/arch/s390/mm/vmem.c
>>> @@ -227,6 +227,14 @@ 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 add1cc7..1384826 100644
>>> --- a/arch/sparc/mm/init_64.c
>>> +++ b/arch/sparc/mm/init_64.c
>>> @@ -2078,6 +2078,14 @@ 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 0075592..4e8f8a4 100644
>>> --- a/arch/x86/mm/init_64.c
>>> +++ b/arch/x86/mm/init_64.c
>>> @@ -1138,6 +1138,125 @@ 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;
>>> +    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;
>>> +    }
>>> +
>>
>> Hi Yasuaki,
>>
>> why call memchr_inv check after memset, this time the page can always 
>> be filled with 0xFD.
>
> The page is not always filled with 0xFD. find_and_clear_pte_page()
> is calld in each section. So the function fills the page
> section size/sizeof(page) byte with 0xFD one time. Thus if section 
> size is
> small, the page is filled with 0xFD.

Hi Yasuaki,

But when section size will be small?

Regards,
Chen

>
> Thanks,
> Yasuaki Ishimatsu
>
>
>>> +    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 c607913..fb0d1fc 100644
>>> --- a/include/linux/mm.h
>>> +++ b/include/linux/mm.h
>>> @@ -1620,6 +1620,8 @@ 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 647a7f2..c54922c 100644
>>> --- a/mm/memory_hotplug.c
>>> +++ b/mm/memory_hotplug.c
>>> @@ -308,19 +308,6 @@ 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;
>>> @@ -337,9 +324,9 @@ 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);
>>>   }
>>>   #else
>>>   static struct page *__kmalloc_section_memmap(unsigned long nr_pages)
>>
>
>
>