* David Hildenbrand <david@xxxxxxxxxx> [2020-07-01 12:15:54]: > On 01.07.20 12:04, Srikar Dronamraju wrote: > > * Michal Hocko <mhocko@xxxxxxxxxx> [2020-07-01 10:42:00]: > > > >> > >>> > >>> 2. Also existence of dummy node also leads to inconsistent information. The > >>> number of online nodes is inconsistent with the information in the > >>> device-tree and resource-dump > >>> > >>> 3. When the dummy node is present, single node non-Numa systems end up showing > >>> up as NUMA systems and numa_balancing gets enabled. This will mean we take > >>> the hit from the unnecessary numa hinting faults. > >> > >> I have to say that I dislike the node online/offline state and directly > >> exporting that to the userspace. Users should only care whether the node > >> has memory/cpus. Numa nodes can be online without any memory. Just > >> offline all the present memory blocks but do not physically hot remove > >> them and you are in the same situation. If users are confused by an > >> output of tools like numactl -H then those could be updated and hide > >> nodes without any memory&cpus. > >> > >> The autonuma problem sounds interesting but again this patch doesn't > >> really solve the underlying problem because I strongly suspect that the > >> problem is still there when a numa node gets all its memory offline as > >> mentioned above. > >> > >> While I completely agree that making node 0 special is wrong, I have > >> still hard time to review this very simply looking patch because all the > >> numa initialization is so spread around that this might just blow up > >> at unexpected places. IIRC we have discussed testing in the previous > >> version and David has provided a way to emulate these configurations > >> on x86. Did you manage to use those instruction for additional testing > >> on other than ppc architectures? > >> > > > > I have tried all the steps that David mentioned and reported back at > > https://lore.kernel.org/lkml/20200511174731.GD1961@xxxxxxxxxxxxxxxxxx/t/#u > > > > As a summary, David's steps are still not creating a memoryless/cpuless on > > x86 VM. > > Now, that is wrong. You get a memoryless/cpuless node, which is *not > online*. Once you hotplug some memory, it will switch online. Once you > remove memory, it will switch back offline. > Let me clarify, we are looking for a node 0 which is cpuless/memoryless at boot. The code in question tries to handle a cpuless/memoryless node 0 at boot. With the steps that you gave the node 0 was always populated, node 1 or some other node would be memoryless/cpuless and offline. But that should have no impact by patch. I don't see how adding/hotplugging/removing memory to a node after boot is going to affect the changes that I have made. Please do correct me if I have misunderstood. -- Thanks and Regards Srikar Dronamraju
