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

From: Jaegeuk Hanse <[email-masked]>
Date: Wed, 21 Nov 2012 13:03:11 +0800

On 11/21/2012 12:42 PM, Wen Congyang wrote:
> At 11/21/2012 12:22 PM, Jaegeuk Hanse Wrote:
>> 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.
> IIRC, we don't touch memblock when hot-add/hot-remove memory. memblock is
> only used for bootmem allocator. I think it isn't used after booting.

In IBM pseries servers.

pseries_remove_memory()
     pseries_remove_memblock()
         memblock_remove()

Furthermore, memblock is set to record available memory ranges get from 
e820 map(you can check it in memblock_x86_fill()) in x86 case, after 
hot-remove memory, this range of memory can't be available, why not 
remove them as pseries servers' codes do.

>> memblock_remove()
>>             __memblock_remove()memory-hotplug: unregister memory section on SPARSEMEM_VMEMMAP
>>
>>                     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?
> No, memblock_isolate_range() can deal with partial overlapped region.
> =====================
> 		if (rbase < base) {
> 			/*
> 			 * @rgn intersects from below.  Split and continue
> 			 * to process the next region - the new top half.
> 			 */
> 			rgn->base = base;
> 			rgn->size -= base - rbase;
> 			type->total_size -= base - rbase;
> 			memblock_insert_region(type, i, rbase, base - rbase,
> 					       memblock_get_region_node(rgn));
> 		} else if (rend > end) {
> 			/*
> 			 * @rgn intersects from above.  Split and redo the
> 			 * current region - the new bottom half.
> 			 */
> 			rgn->base = end;
> 			rgn->size -= end - rbase;
> 			type->total_size -= end - rbase;
> 			memblock_insert_region(type, i--, rbase, end - rbase,
> 					       memblock_get_region_node(rgn));
> =====================
>
> If the region is partial overlapped region, we will split the old region into
> two regions. After doing this, it is full contained region now.

You are right, I misunderstand the codes.

>
> Thanks
> Wen Congyang
>
>> 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)
>>