RFR (M): 8137082: Factor out G1 prediction code from G1CollectorPolicy and clean up

[Thomas Schatzl]

Hi Jon,

On Thu, 2015-10-01 at 08:25 -0700, Jon Masamitsu wrote:
> Thomas,
> 
> Looks good.  Thanks for the changes.
> 
> In g1Predictions.cpp you set epsilon to 1e-6.
> Is that value based on what you've seen as
> being needed to avoid floating point inaccuracies?
> Or just a nice conservative number that should never
> fail?
> 

The 1e-6 is just some typical "small" number to counter floating point
representation problems during comparison.
It has nothing to do with the prediction at all.

Let me see if I can find something like that in the existing code.

> If you decide to add a comment about what this code
> is trying to do (as I requested in my last mail)
> 
>   469   if ((2.0 /* magic */ * _predictor.sigma()) * (double) bytes_to_copy > (double) free_bytes) {
> 
> I don't need a new webrev.

I added comments to JDK-8138684. I expect that to be fixed soon, the
current code makes G1 take too much risk in adding regions, potentially
causing evacuation failures. This degrades the G1 experience :)

Thanks,
  Thomas