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

Wen Congyang
2012-11-21T02:59:25Z

At 11/20/2012 07:16 PM, Jaegeuk Hanse Wrote:
> On 11/01/2012 05:44 PM, Wen Congyang wrote:
>> From: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
>>
>> 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.

Thanks
Wen Congyang
>
> Regards,
> Jaegeuk
>
>>
>> CC: David Rientjes <rientjes@google.com>
>> CC: Jiang Liu <liuj97@gmail.com>
>> CC: Len Brown <len.brown@intel.com>
>> CC: Christoph Lameter <cl@linux.com>
>> Cc: Minchan Kim <minchan.kim@gmail.com>
>> CC: Andrew Morton <akpm@linux-foundation.org>
>> CC: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
>> CC: Wen Congyang <wency@cn.fujitsu.com>
>> Signed-off-by: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
>> ---
>> 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)
>
>