For environments with memory oversubsription should we enable ksm?

[Alexander Bozhenko]

We probably need to enable kernel same-page mergings:

https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/6/html-single/Virtualization_Administration_Guide/index.html#chap-KSM
http://www.linux-kvm.org/page/KSM
https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/6/html-single/Virtualization_Tuning_and_Optimization_Guide/index.html#sect-Virtualization_Tuning_Optimization_Guide-NUMA-NUMA_KSM

This should be tested in our lab.

[Alexander Bozhenko (alexbozhenko)]

From
http://searchenterpriselinux.techtarget.com/tip/How-to-improve-KVM-performance-by-adjusting-KSM

"Determining whether to use KSM, or turn it off:
If the purpose is to run as many VMs as possible, and performance is not an issue, KSM should be kept running. For example, it allows running 40 VMs on a host normally capable of running 30 VMs, which means maximum hardware usage efficiency. But, if a server is running with a relatively small amount of VMs and performance is an issue, KSM should be turned off."

[Dmitry Mescheryakov (dmitrymex)]

Alexander, however small the item seems to be, it is outside of general bug fixing workflow: we need several relevant people to review your proposal and see if we can apply it and for which environments. Then it should be implemented and tested. So I am marking current bug as invalid. Please file a feature request into MOS backlog instead.