On Wed 01-07-20 13:30:57, David Hildenbrand wrote: > On 01.07.20 13:06, David Hildenbrand wrote: > > On 01.07.20 13:01, Srikar Dronamraju wrote: > >> * 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. I would really appreciate a feedback to these two as well. > >>>>> 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. > > > > I was just correcting your statement, because it was wrong. > > > > Could be that x86 code maps PXM 1 to node 0 because PXM 1 does neither > > have CPUs nor memory. That would imply that we can, in fact, never have > > node 0 offline during boot. > > > > Yep, looks like it. > > [ 0.009726] SRAT: PXM 1 -> APIC 0x00 -> Node 0 > [ 0.009727] SRAT: PXM 1 -> APIC 0x01 -> Node 0 > [ 0.009727] SRAT: PXM 1 -> APIC 0x02 -> Node 0 > [ 0.009728] SRAT: PXM 1 -> APIC 0x03 -> Node 0 > [ 0.009731] ACPI: SRAT: Node 0 PXM 1 [mem 0x00000000-0x0009ffff] > [ 0.009732] ACPI: SRAT: Node 0 PXM 1 [mem 0x00100000-0xbfffffff] > [ 0.009733] ACPI: SRAT: Node 0 PXM 1 [mem 0x100000000-0x13fffffff] This begs a question whether ppc can do the same thing? I would swear that we've had x86 system with node 0 but I cannot really find it and it is possible that it was not x86 after all... -- Michal Hocko SUSE Labs
