On Wed 19-06-19 10:54:08, David Hildenbrand wrote: > 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). Well, I am not sure we really have to care about mutli-nodes memblocks much. The API is clumsy but does anybody actually care? The vast majority of hotplug usecases simply do not do that in the first place right? And if they do need a smaller granularity to describe their memory topology then we need a different user API rather the fiddle with implementation details I would argue. -- Michal Hocko SUSE Labs
