On 01.07.20 12:04, Srikar Dronamraju wrote:
> * Michal Hocko <mho...@kernel.org> [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.gd1...@linux.vnet.ibm.com/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.


David / dhildenb

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