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

From: Wen Congyang <[email-masked]>
Date: Wed, 21 Nov 2012 12:42:41 +0800

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.

> 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?

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.

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)
>>>
> 
>