Subject: Re: [PATCH v3 06/12] memory-hotplug: unregister memory section on SPARSEMEM_VMEMMAP

From: Jaegeuk Hanse <[email-masked]>
Date: Wed, 21 Nov 2012 12:22:52 +0800

On 11/21/2012 11:05 AM, Wen Congyang wrote:
> At 11/20/2012 07:16 PM, Jaegeuk Hanse Wrote:
>> On 11/01/2012 05:44 PM, Wen Congyang wrote:
>>> From: Yasuaki Ishimatsu <[email-masked]>
>>>
>>> Currently __remove_section for SPARSEMEM_VMEMMAP does nothing. But
>>> even if
>>> we use SPARSEMEM_VMEMMAP, we can unregister the memory_section.
>>>
>>> So the patch add unregister_memory_section() into __remove_section().
>> Hi Yasuaki,
>>
>> I have a question about these sparse vmemmap memory related patches. Hot
>> add memory need allocated vmemmap pages, but this time is allocated by
>> buddy system. How can gurantee virtual address is continuous to the
>> address allocated before? If not continuous, page_to_pfn and pfn_to_page
>> can't work correctly.
> vmemmap has its virtual address range:
> ffffea0000000000 - ffffeaffffffffff (=40 bits) virtual memory map (1TB)
>
> We allocate memory from buddy system to store struct page, and its virtual
> address isn't in this range. So we should update the page table:
>
> kmalloc_section_memmap()
>      sparse_mem_map_populate()
>          pfn_to_page() // get the virtual address in the vmemmap range
>          vmemmap_populate() // we update page table here
>
> When we use vmemmap, page_to_pfn() always returns address in the vmemmap
> range, not the address that kmalloc() returns. So the virtual address
> is continuous.

Hi Congyang,

Another question about memory hotplug. During hot remove memory, it will 
also call memblock_remove to remove related memblock.
memblock_remove()
            __memblock_remove()
                    memblock_isolate_range()
                    memblock_remove_region()

But memblock_isolate_range() only record fully contained regions, 
regions which are partial overlapped just be splitted instead of record. 
So these partial overlapped regions can't be removed. Where I miss?

Regards,
Jaegeuk

> Thanks
> Wen Congyang
>> Regards,
>> Jaegeuk
>>
>>> CC: David Rientjes <[email-masked]>
>>> CC: Jiang Liu <[email-masked]>
>>> CC: Len Brown <[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]>
>>> ---
>>>    mm/memory_hotplug.c | 13 ++++++++-----
>>>    1 file changed, 8 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>>> index ca07433..66a79a7 100644
>>> --- a/mm/memory_hotplug.c
>>> +++ b/mm/memory_hotplug.c
>>> @@ -286,11 +286,14 @@ static int __meminit __add_section(int nid,
>>> struct zone *zone,
>>>    #ifdef CONFIG_SPARSEMEM_VMEMMAP
>>>    static int __remove_section(struct zone *zone, struct mem_section *ms)
>>>    {
>>> -    /*
>>> -     * XXX: Freeing memmap with vmemmap is not implement yet.
>>> -     *      This should be removed later.
>>> -     */
>>> -    return -EBUSY;
>>> +    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)
>>