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. -- Michal Hocko SUSE Labs
