Subject: Re: [Patch v4 08/12] memory-hotplug: remove memmap of sparse-vmemmap

From: Jianguo Wu <[email-masked]>
Date: Fri, 7 Dec 2012 10:20:16 +0800

Hi Tang,

On 2012/12/7 9:42, Tang Chen wrote:

> Hi Wu,
> 
> I met some problems when I was digging into the code. It's very
> kind of you if you could help me with that. :)
> 
> If I misunderstood your code, please tell me.
> Please see below. :)
> 
> On 12/03/2012 10:23 AM, Jianguo Wu wrote:
>> Signed-off-by: Jianguo Wu<[email-masked]>
>> Signed-off-by: Jiang Liu<[email-masked]>
>> ---
>>   include/linux/mm.h  |    1 +
>>   mm/sparse-vmemmap.c |  231 +++++++++++++++++++++++++++++++++++++++++++++++++++
>>   mm/sparse.c         |    3 +-
>>   3 files changed, 234 insertions(+), 1 deletions(-)
>>
>> diff --git a/include/linux/mm.h b/include/linux/mm.h
>> index 5657670..1f26af5 100644
>> --- a/include/linux/mm.h
>> +++ b/include/linux/mm.h
>> @@ -1642,6 +1642,7 @@ 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_free(struct page *memmap, unsigned long nr_pages);
>>
>>   enum mf_flags {
>>       MF_COUNT_INCREASED = 1<<  0,
>> diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c
>> index 1b7e22a..748732d 100644
>> --- a/mm/sparse-vmemmap.c
>> +++ b/mm/sparse-vmemmap.c
>> @@ -29,6 +29,10 @@
>>   #include<asm/pgalloc.h>
>>   #include<asm/pgtable.h>
>>
>> +#ifdef CONFIG_MEMORY_HOTREMOVE
>> +#include<asm/tlbflush.h>
>> +#endif
>> +
>>   /*
>>    * Allocate a block of memory to be used to back the virtual memory map
>>    * or to back the page tables that are used to create the mapping.
>> @@ -224,3 +228,230 @@ void __init sparse_mem_maps_populate_node(struct page **map_map,
>>           vmemmap_buf_end = NULL;
>>       }
>>   }
>> +
>> +#ifdef CONFIG_MEMORY_HOTREMOVE
>> +
>> +#define PAGE_INUSE 0xFD
>> +
>> +static void vmemmap_free_pages(struct page *page, int order)
>> +{
>> +    struct zone *zone;
>> +    unsigned long magic;
>> +
>> +    magic = (unsigned long) page->lru.next;
>> +    if (magic == SECTION_INFO || magic == MIX_SECTION_INFO) {
>> +        put_page_bootmem(page);
>> +
>> +        zone = page_zone(page);
>> +        zone_span_writelock(zone);
>> +        zone->present_pages++;
>> +        zone_span_writeunlock(zone);
>> +        totalram_pages++;
>> +    } else
>> +        free_pages((unsigned long)page_address(page), order);
> 
> Here, I think SECTION_INFO and MIX_SECTION_INFO pages are all allocated
> by bootmem, so I put this function this way.
> 
> I'm not sure if parameter order is necessary here. It will always be 0
> in your code. Is this OK to you ?
> 

parameter order is necessary in cpu_has_pse case:
	vmemmap_pmd_remove
		free_pagetable(pmd_page(*pmd), get_order(PMD_SIZE))

> static void free_pagetable(struct page *page)
> {
>         struct zone *zone;
>         bool bootmem = false;
>         unsigned long magic;
> 
>         /* bootmem page has reserved flag */
>         if (PageReserved(page)) {
>                 __ClearPageReserved(page);
>                 bootmem = true;
>         }
> 
>         magic = (unsigned long) page->lru.next;
>         if (magic == SECTION_INFO || magic == MIX_SECTION_INFO)
>                 put_page_bootmem(page);
>         else
>                 __free_page(page);
> 
>         /*
>          * SECTION_INFO pages and MIX_SECTION_INFO pages
>          * are all allocated by bootmem.
>          */
>         if (bootmem) {
>                 zone = page_zone(page);
>                 zone_span_writelock(zone);
>                 zone->present_pages++;
>                 zone_span_writeunlock(zone);
>                 totalram_pages++;
>         }
> }
> 
> (snip)
> 
>> +
>> +static void vmemmap_pte_remove(pmd_t *pmd, unsigned long addr, unsigned long end)
>> +{
>> +    pte_t *pte;
>> +    unsigned long next;
>> +    void *page_addr;
>> +
>> +    pte = pte_offset_kernel(pmd, addr);
>> +    for (; addr<  end; pte++, addr += PAGE_SIZE) {
>> +        next = (addr + PAGE_SIZE)&  PAGE_MASK;
>> +        if (next>  end)
>> +            next = end;
>> +
>> +        if (pte_none(*pte))
> 
> Here, you checked xxx_none() in your vmemmap_xxx_remove(), but you used
> !xxx_present() in your x86_64 patches. Is it OK if I only check
> !xxx_present() ?

It is Ok.

> 
>> +            continue;
>> +        if (IS_ALIGNED(addr, PAGE_SIZE)&&
>> +            IS_ALIGNED(next, PAGE_SIZE)) {
>> +            vmemmap_free_pages(pte_page(*pte), 0);
>> +            spin_lock(&init_mm.page_table_lock);
>> +            pte_clear(&init_mm, addr, pte);
>> +            spin_unlock(&init_mm.page_table_lock);
>> +        } else {
>> +            /*
>> +             * Removed page structs are filled with 0xFD.
>> +             */
>> +            memset((void *)addr, PAGE_INUSE, next - addr);
>> +            page_addr = page_address(pte_page(*pte));
>> +
>> +            if (!memchr_inv(page_addr, PAGE_INUSE, PAGE_SIZE)) {
>> +                spin_lock(&init_mm.page_table_lock);
>> +                pte_clear(&init_mm, addr, pte);
>> +                spin_unlock(&init_mm.page_table_lock);
> 
> Here, since we clear pte, we should also free the page, right ?
> 

Right, I forgot here, sorry.

>> +            }
>> +        }
>> +    }
>> +
>> +    free_pte_table(pmd);
>> +    __flush_tlb_all();
>> +}
>> +
>> +static void vmemmap_pmd_remove(pud_t *pud, unsigned long addr, unsigned long end)
>> +{
>> +    unsigned long next;
>> +    pmd_t *pmd;
>> +
>> +    pmd = pmd_offset(pud, addr);
>> +    for (; addr<  end; addr = next, pmd++) {
>> +        next = (addr, end);
> 
> And by the way, there isn't pte_addr_end() in kernel, why ?
> I saw you calculated it like this:
> 
>                 next = (addr + PAGE_SIZE) & PAGE_MASK;
>                 if (next > end)
>                         next = end;
> 
> This logic is very similar to {pmd|pud|pgd}_addr_end(). Shall we add a
> pte_addr_end() or something ? :)

Maybe just keep this for now if no other place need pte_addr_end()?

> Since there is no such code in kernel for a long time, I think there
> must be some reasons.

Maybe in current kernel, doesn't deal not PTE_SIZE alignment address？

> 
> I merged free_xxx_table() and remove_xxx_table() as common interfaces.

Greate!

Thanks for your work:).

> 
> And again, thanks for your patient and nice explanation. :)
> 
> (snip)
> 
> .
>