linux-kernel - Re: [PATCH v3 06/12] memory-hotplug: unregister memory section on SPARSEMEM

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Date:	Wed, 21 Nov 2012 11:05:41 +0800
From:	Wen Congyang <wency@...fujitsu.com>
To:	Jaegeuk Hanse <jaegeuk.hanse@...il.com>
CC:	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>, x86@...nel.org,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org, linux-acpi@...r.kernel.org,
	linux-s390@...r.kernel.org, linux-sh@...r.kernel.org,
	linux-ia64@...r.kernel.org, cmetcalf@...era.com,
	sparclinux@...r.kernel.org, David Rientjes <rientjes@...gle.com>,
	Jiang Liu <liuj97@...il.com>, Len Brown <len.brown@...el.com>,
	benh@...nel.crashing.org, paulus@...ba.org,
	Christoph Lameter <cl@...ux.com>,
	Minchan Kim <minchan.kim@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Jianguo Wu <wujianguo@...wei.com>
Subject: Re: [PATCH v3 06/12] memory-hotplug: unregister memory section on
 SPARSEMEM_VMEMMAP

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@...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@...gle.com>
>> CC: Jiang Liu <liuj97@...il.com>
>> CC: Len Brown <len.brown@...el.com>
>> CC: Christoph Lameter <cl@...ux.com>
>> Cc: Minchan Kim <minchan.kim@...il.com>
>> CC: Andrew Morton <akpm@...ux-foundation.org>
>> CC: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
>> CC: Wen Congyang <wency@...fujitsu.com>
>> Signed-off-by: Yasuaki Ishimatsu <isimatu.yasuaki@...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)
> 
> 

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