KSM is enabled by handler at 80% mem utilization (by default).
However, KSM takes a while to have a positive effect on the memory consumption (aka reduce memory load).

The problem is if memory keeps increasing after going beyond 80% and will eventually hit the hard-eviction threshold of the node, which will then lead to eviction of VMs.

4.20

Always

1. Create many VMs which will eventually use (in sum) 95% of the allocatable memory of a node (or as much as possible)
2. Hard eviction (or soft eviciton if configured) will be triggered
3. 

Some VMs will be evicted

KSM is enabled earlier in order to avoid running out of memory

Enabling KSM earlier is not solving this test-case per se, because if VMs start to too quickly consume memory, then we will still run out of it.
Thus starting it earlier is just improving the situation.