RFR: Handle metadata induced GC

[Aleksey Shipilev]

On 10/26/2018 05:52 PM, Zhengyu Gu wrote:
> Updated patch is based on current head without any refactoring.
> 
> Instead of introducing asynchronous GC, the new approach communicates metaspace OOM by informing GC
> heuristics, and allows it to start new GC cycle early and performs classes unloading, etc.
> 
> http://cr.openjdk.java.net/~zgu/shenandoah/metadata_gc/webrev.01/

All right!

It still feels awkward to force Full GC on Metaspace OOM. We can technically do the concurrent cycle
with class unloading enabled, are we? This can be a good follow-up.

I think you can make _metaspace_oom cleaner if you reuse ShenandoahSharedFlag.

-Aleksey