RFR (S): 6490394: G1: Allow heap shrinking / memory unmapping after reclaiming regions during Remark

[Ruslan Synytsky]

Dear Thomas and Sangheon, hope you are doing great.

I just noticed an important improvement related to vertical scaling and
would like to clarify details mentioned in the release notes
<https://bugs.openjdk.java.net/browse/JDK-8211756>

*> By default, G1 may now give back Java heap memory to the operating
system during any concurrent mark cycle. G1 will respect default Java heap
sizing policies at that time. *
Does it mean that G1 is smart enough now by default and users do not need
to deal with *loadaverage* and *G1PeriodicGCInterval *that we introduced in JEP
346 <https://bugs.openjdk.java.net/browse/JDK-8204089>?

*> This behavior may be disabled by changing minimum Java heap size via the
-Xms option.*
At the same time if a user adjusts Xms option then he/she does not get this
"smart behaviour" at all.

Are these rephrased statements correct?

Thank you
-- 
Ruslan
CEO @ Jelastic <https://jelastic.com/>
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