Strange behaviour on half-occupied heap

[Roman Kennke]

>> Even with -XX:ShenandoahMaxCSetFactor=60 same situation reproduces. 
>>
>> I recorded visualiser:
>> https://drive.google.com/file/d/1uhJiGE3kCCDZNbOds6G853u7AmSlPbs0/view?usp=sharing
> 
> Aha. Heuristics have run is into the corner: there is no space to evacuate to with concurrent GC,
> and all we are left to do is Full GC. I think I know what to do -- we have the "evacuation reserve"
> patch that we need to get in, so heap always have some reserved space to evacuate to.

Yeah, evac-reserve would be nice. But it still smells like something
else might be wrong: with that much garbage shouldn't it be able to
reclaim enough to maintain headroom for evac? Why is that not working?

Disclaimer: I haven't studied the logs much. I'm mostly on the phone
currently (on vacation). Please help me ;-)

Roman