Re: [PATCH v2] mm/sparse: set section nid for hot-add memory

[Wei Yang <richardw.yang@linux.intel.com>]

On Tue, Jun 18, 2019 at 09:49:48AM +0200, Oscar Salvador wrote:
>On Tue, Jun 18, 2019 at 08:55:37AM +0800, Wei Yang wrote:
>> In case of NODE_NOT_IN_PAGE_FLAGS is set, we store section's node id in
>> section_to_node_table[]. While for hot-add memory, this is missed.
>> Without this information, page_to_nid() may not give the right node id.
>> 
>> BTW, current online_pages works because it leverages nid in memory_block.
>> But the granularity of node id should be mem_section wide.
>
>I forgot to ask this before, but why do you mention online_pages here?
>IMHO, it does not add any value to the changelog, and it does not have much
>to do with the matter.
>

Since to me it is a little confused why we don't set the node info but still
could online memory to the correct node. It turns out we leverage the
information in memblock.

>online_pages() works with memblock granularity and not section granularity.
>That memblock is just a hot-added range of memory, worth of either 1 section or multiple
>sections, depending on the arch or on the size of the current memory.
>And we assume that each hot-added memory all belongs to the same node.
>

So I am not clear about the granularity of node id. section based or memblock
based. Or we have two cases:

* for initial memory, section wide
* for hot-add memory, mem_block wide

>
>> Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>
>> Reviewed-by: Oscar Salvador <osalvador@suse.de>
>> Reviewed-by: David Hildenbrand <david@redhat.com>
>> Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
>> 
>> ---
>> v2:
>>   * specify the case NODE_NOT_IN_PAGE_FLAGS is effected.
>>   * list one of the victim page_to_nid()
>> 
>> ---
>>  mm/sparse.c | 1 +
>>  1 file changed, 1 insertion(+)
>> 
>> diff --git a/mm/sparse.c b/mm/sparse.c
>> index 4012d7f50010..48fa16038cf5 100644
>> --- a/mm/sparse.c
>> +++ b/mm/sparse.c
>> @@ -733,6 +733,7 @@ int __meminit sparse_add_one_section(int nid, unsigned long start_pfn,
>>  	 */
>>  	page_init_poison(memmap, sizeof(struct page) * PAGES_PER_SECTION);
>>  
>> +	set_section_nid(section_nr, nid);
>>  	section_mark_present(ms);
>>  	sparse_init_one_section(ms, section_nr, memmap, usemap);
>>  
>> -- 
>> 2.19.1
>> 
>
>-- 
>Oscar Salvador
>SUSE L3

-- 
Wei Yang
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