Re: [PATCH v2 3/3] mm/page_alloc: Keep memoryless cpuless node 0 offline

David Hildenbrand
2020-05-12T07:49:20Z

On 11.05.20 19:47, Srikar Dronamraju wrote:
> * David Hildenbrand <david@redhat.com> [2020-05-08 15:42:12]:
>
> Hi David,
>
> Thanks for the steps to tryout.
>
>>>
>>> #! /bin/bash
>>> sudo x86_64-softmmu/qemu-system-x86_64 \
>>> --enable-kvm \
>>> -m 4G,maxmem=20G,slots=2 \
>>> -smp sockets=2,cores=2 \
>>> -numa node,nodeid=0,cpus=0-1,mem=4G -numa node,nodeid=1,cpus=2-3,mem=0G \
>>
>> Sorry, this line has to be
>>
>> -numa node,nodeid=0,cpus=0-3,mem=4G -numa node,nodeid=1,mem=0G \
>>
>>> -kernel /home/dhildenb/git/linux/arch/x86_64/boot/bzImage \
>>> -append "console=ttyS0 rd.shell rd.luks=0 rd.lvm=0 rd.md=0 rd.dm=0" \
>>> -initrd /boot/initramfs-5.2.8-200.fc30.x86_64.img \
>>> -machine pc,nvdimm \
>>> -nographic \
>>> -nodefaults \
>>> -chardev stdio,id=serial \
>>> -device isa-serial,chardev=serial \
>>> -chardev socket,id=monitor,path=/var/tmp/monitor,server,nowait \
>>> -mon chardev=monitor,mode=readline
>>>
>>> to get a cpu-less and memory-less node 1. Never tried with node 0.
>>>
>
> I tried
>
> qemu-system-x86_64 -enable-kvm -m 4G,maxmem=20G,slots=2 -smp sockets=2,cores=2 -cpu host -numa node,nodeid=0,cpus=0-3,mem=4G -numa node,nodeid=1,mem=0G -vga none -nographic -serial mon:stdio /home/srikar/fedora.qcow2
>
> and the resulting guest was.
>
> [root@localhost ~]# numactl -H
> available: 1 nodes (0)
> node 0 cpus: 0 1 2 3
> node 0 size: 3927 MB
> node 0 free: 3316 MB
> node distances:
> node 0
> 0: 10
>
> [root@localhost ~]# lscpu
> Architecture: x86_64
> CPU op-mode(s): 32-bit, 64-bit
> Byte Order: Little Endian
> Address sizes: 40 bits physical, 48 bits virtual
> CPU(s): 4
> On-line CPU(s) list: 0-3
> Thread(s) per core: 1
> Core(s) per socket: 2
> Socket(s): 2
> NUMA node(s): 1
> Vendor ID: GenuineIntel
> CPU family: 6
> Model: 46
> Model name: Intel(R) Xeon(R) CPU X7560 @ 2.27GHz
> Stepping: 6
> CPU MHz: 2260.986
> BogoMIPS: 4521.97
> Virtualization: VT-x
> Hypervisor vendor: KVM
> Virtualization type: full
> L1d cache: 32K
> L1i cache: 32K
> L2 cache: 4096K
> L3 cache: 16384K
> NUMA node0 CPU(s): 0-3
> Flags: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx rdtscp lm constant_tsc arch_perfmon rep_good nopl xtopology cpuid tsc_known_freq pni vmx ssse3 cx16 sse4_1 sse4_2 x2apic popcnt tsc_deadline_timer hypervisor lahf_lm cpuid_fault pti ssbd ibrs ibpb tpr_shadow vnmi flexpriority ept vpid tsc_adjust arat umip arch_capabilities
>
> [root@localhost ~]# cat /sys/devices/system/node/online
> 0
> [root@localhost ~]# cat /sys/devices/system/node/possible
> 0-1
>
> ---------------------------------------------------------------------------------
>
> I also tried
>
> qemu-system-x86_64 -enable-kvm -m 4G,maxmem=20G,slots=2 -smp sockets=2,cores=2 -cpu host -numa node,nodeid=1,cpus=0-3,mem=4G -numa node,nodeid=0,mem=0G -vga none -nographic -serial mon:stdio /home/srikar/fedora.qcow2
>
> and the resulting guest was.
>
> [root@localhost ~]# numactl -H
> available: 1 nodes (0)
> node 0 cpus: 0 1 2 3
> node 0 size: 3927 MB
> node 0 free: 3316 MB
> node distances:
> node 0
> 0: 10
>
> [root@localhost ~]# lscpu
> Architecture: x86_64
> CPU op-mode(s): 32-bit, 64-bit
> Byte Order: Little Endian
> Address sizes: 40 bits physical, 48 bits virtual
> CPU(s): 4
> On-line CPU(s) list: 0-3
> Thread(s) per core: 1
> Core(s) per socket: 2
> Socket(s): 2
> NUMA node(s): 1
> Vendor ID: GenuineIntel
> CPU family: 6
> Model: 46
> Model name: Intel(R) Xeon(R) CPU X7560 @ 2.27GHz
> Stepping: 6
> CPU MHz: 2260.986
> BogoMIPS: 4521.97
> Virtualization: VT-x
> Hypervisor vendor: KVM
> Virtualization type: full
> L1d cache: 32K
> L1i cache: 32K
> L2 cache: 4096K
> L3 cache: 16384K
> NUMA node0 CPU(s): 0-3
> Flags: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx rdtscp lm constant_tsc arch_perfmon rep_good nopl xtopology cpuid tsc_known_freq pni vmx ssse3 cx16 sse4_1 sse4_2 x2apic popcnt tsc_deadline_timer hypervisor lahf_lm cpuid_fault pti ssbd ibrs ibpb tpr_shadow vnmi flexpriority ept vpid tsc_adjust arat umip arch_capabilities
>
> [root@localhost ~]# cat /sys/devices/system/node/online
> 0
> [root@localhost ~]# cat /sys/devices/system/node/possible
> 0-1
>
> Even without my patch, both the combinations, I am still unable to see a
> cpuless, memoryless node being online. And the interesting part being even

Yeah, I think on x86, all memory-less and cpu-less nodes are offline as
default. Especially when hotunplugging cpus/memory, we set them offline
as well.

But as Michal mentioned, the node handling code is complicated and
differs between various architectures.

> if I mark node 0 as cpuless,memoryless and node 1 as actual node, the system
> somewhere marks node 0 as the actual node.

Is the kernel maybe mapping PXM 1 to node 0 in that case, because it
always requires node 0 to be online/contain memory? Would be interesting
what happens if you hotplug a DIMM to (QEMU )node 0 - if PXM 0 will be
mapped to node 1 then as well.

--
Thanks,

David / dhildenb