On 29/11/16 11:42, Tejun Heo wrote: > Hello, Balbir. > > On Tue, Nov 29, 2016 at 11:09:26AM +1100, Balbir Singh wrote: >> On 29/11/16 08:10, Tejun Heo wrote: >>> On Thu, Nov 24, 2016 at 12:05:12AM +1100, Balbir Singh wrote: >>>> On my desktop NODES_SHIFT is 6, many distro kernels have it a 9. I've known >>>> of solutions that use fake NUMA for partitioning and need as many nodes as >>>> possible. >>> >>> It was a crude kludge that people used before memcg. If people still >>> use it, that's fine but we don't want to optimize / make code >>> complicated for it, so let's please put away this part of >>> justification. >> >> Are you suggesting those use cases can be ignored now? > > Don't do that. When did I say that? What I said is that it isn't a > good idea to optimize and complicate the code base for it at this > point. It shouldn't a controversial argument given fake numa's > inherent issues and general lack of popularity. > > Besides, does node hotplug even apply to fake numa? ISTR it being > configured statically on the boot prompt. Good point, not sure if it worked with that setup as well. > >>> NUMA code already has possible detection. Why not simply make memcg >>> use those instead of MAX_NUMNODES like how we use nr_cpu_ids instead >>> of NR_CPUS? >> >> nodes_possible_map is set to node_online_map at the moment for ppc64. >> Which becomes a problem when hotplugging a node that was not already >> online. >> >> I am not sure what you mean by possible detection. node_possible_map >> is set based on CONFIG_NODE_SHIFT and then can be adjusted by the >> architecture (if desired). Are you suggesting firmware populate it >> in? > > That's what we do with cpus. The kernel is built with high maximum > limit and the kernel queries the firmware during boot to determine how > many are actually possible on the system, which in most cases isn't > too far from what's already on the system. I don't see why we would > take a different approach with NUMA nodes. Agreed for the short term. I think memory hotplug needs a review and we'll probably get it fixed as we make progress along the way Balbir -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>