On 19.06.19 08:10, Michal Hocko wrote: > On Tue 18-06-19 10:40:06, David Hildenbrand wrote: >> On 18.06.19 10:32, Wei Yang wrote: >>> 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. >> >> I'd also drop the comment here. >> >>> >>>> 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 >> >> It's all a big mess. Right now, you can offline initial memory with >> mixed nodes. Also on my list of many ugly things to clean up. >> >> (I even remember that we can have mixed nodes within a section, but I >> haven't figured out yet how that is supposed to work in some scenarios) > > Yes, that is indeed the case. See 4aa9fc2a435abe95a1e8d7f8c7b3d6356514b37a. > How to fix this? Well, I do not think we can. Section based granularity > simply doesn't agree with the reality and so we have to live with that. > There is a long way to remove all those section size assumptions from > the code though. > Trying to remove NODE_NOT_IN_PAGE_FLAGS could work, but we would have to identify how exactly needs that. For memory blocks, we need a different approach (I have in my head to make ->nid indicate if we are dealing with mixed nodes. If mixed, disallow onlining/offlining). -- Thanks, David / dhildenb
