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

From: Yasuaki Ishimatsu <[email-masked]>
Date: Thu, 4 Oct 2012 15:26:36 +0900

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.

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)
>