Automatic Online of hotplugged memory

[Abbasali Companywala]

Hi,

I am trying to perform memory hotplug on an Ubuntu 16.04 qemu\kvm guest 
and while I can successfully add memory, the added memory doesn't 
automatically come online. After doing a bit of research I found out 
that there is a kernel config option called 
"CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE" which needs to be enabled to have 
automatic onlining of hotplugged memory. However, this option is not 
available on the Ubuntu 16.04 which comes with a default kernel of 
4.4.0-62-generic. I can get around this issue by creating a udev rule to 
online memory. I was wondering if this is a bug that needs to be reported?

#Setup info:
Host: Oracle Linux 7.4 + qemu2.9.0-3 + UEK 4.1.12-94.3.9
Guest: Ubuntu 16.04 with default kernel 4.4.0-62-generic
root at ubuntu-uefi-L1:~# cat /boot/config-4.4.0-62-generic | grep 
CONFIG_MEMORY_HOTPLUG
CONFIG_MEMORY_HOTPLUG=y
CONFIG_MEMORY_HOTPLUG_SPARSE=y

This issue doesn't exist in Ubuntu 16.10 which comes with the 
4.8.0-22-generic default kernel.
acompany at acompanyPC:~$ cat /boot/config-4.8.0-22-generic | grep 
CONFIG_MEMORY_HOTPLUG
CONFIG_MEMORY_HOTPLUG=y
CONFIG_MEMORY_HOTPLUG_SPARSE=y
CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE=y

Thanks,

Abbas Companywala

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