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

From: Jaegeuk Hanse <[email-masked]>
Date: Tue, 20 Nov 2012 14:58:34 +0800

On 11/20/2012 02:55 PM, Wen Congyang wrote:
> At 11/20/2012 02:22 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,
>>
>> In order to review this patch, I should dig sparse memory codes in
>> advance. But I have some confuse of codes. Why need encode/decode mem
>> map instead of set mem_map to ms->section_mem_map directly?
> The memmap is aligned, and the low bits are zero. We store some information
> in these bits. So we need to encode/decode memmap here.

Hi Congyang,

Thanks for you reponse. But I mean why return (unsigned long)(mem_map - 
(section_nr_to_pfn(pnum))); in function sparse_encode_mem_map, and then 
return ((struct page *)coded_mem_map) + section_nr_to_pfn(pnum); in 
funtion sparse_decode_mem_map instead of just store mem_map in 
ms->section_mep_map directly.

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)
>>