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. -- Thanks, David / dhildenb
