RFR (M): 8212657: Implementation of JDK-8204089 Timely Reduce Unused Committed Memory

[Thomas Schatzl]

Hi Sunny,

On Wed, 2018-11-14 at 12:07 +0100, Thomas Schatzl wrote:
> Hi,
> 
> On Wed, 2018-11-14 at 10:49 +0000, Sunny Chan, CLSA wrote:
> > I think my main concern is that this is a departure from the norm
> > in the VM. The use of "peridodic gc" reminds me of the RMI DGC
> > hourly 
> 
> Both Shenandoah and ZGC have some sort of periodic GC. Their GC
> pauses are of course much lower.
> 
> > Full GC saga where it causes random pauses that is not known and
> > eventually everyone pretty much disabled it by default. Although it
> > is a concurrent cycle and the impact is supposedly small, I suspect
> > there will be other unintended consequences and effects that would
> > be discovered when we move to production. However I can see that
> > for a lot of docker/cloud workload this would be a beneficial.
> 
> Thank you for the historical perspective. Maybe it is some case of
> good intentions cause havoc, what do others think?
> 
> We can disable these periodic GCs by default for now and look at the
> adoption rate. It is also opt-in for J9.

I asked around within the team and there is a slight preference to
making the periodic GCs opt-in (setting G1PeriodicGCInterval to 0).
This also saves us to think of a good value for that.

I will update the JEP and CSR as soon there is some consensus about
this and actually how to determine when such a GC should be started.

The updated webrev link will be sent out in response to StefanJ's
review comments.

Thanks,
  Thomas