RFR(XS): 8001425: G1: Change the default values for certain G1 specific flags

John Cuthbertson john.cuthbertson at oracle.com
Thu Jan 10 18:47:38 UTC 2013

Hi Bengt,

Thanks for reviewing the code. Replies inline...

On 1/10/2013 2:07 AM, Bengt Rutisson wrote:
> Hi John,
> Changes look good.
> One question about G1NewSizePercent and G1MaxNewSizePercent. Why are 
> these only changed for heap sizes below 4GB? I would think that at 
> least the reduction of G1NewSizePercent would be even more important 
> for larger heap sizes. If we want to get lower pause times on larger 
> heaps we need to be able to have a small young gen size.

The simple answer is: it was suggested by Monica and Charlie. Personally 
I'm OK with making the new values of G1NewSizePercent and 
G1MaxNewSizePercent the defaults for all heap sizes and we might (or 
most likely will) go there in the future - but for the moment we're 
being conservative.

As I mentioned we would like to make G1 a bit more adaptive - and both 
Monica and Charlie have some ideas in that area.

> Also, your change in arguments.cpp is guarded by #ifndef SERIALGC. 
> This is correct of course, but Joe Provino has a change out that will 
> replace this kind of check with #if INCLUDE_ALL_GCS:
> http://cr.openjdk.java.net/~jprovino/8005915/webrev.00
> Neither you nor Joe will get any merge conflicts if your changes are 
> both pushed. It will even still compile. But the code inside #ifndef 
> SERIALGC will never be executed. So, it might be good to keep any eye 
> out for how Joe's change propagate through the repositories to make 
> sure that you can manually resolve this.
> My guess is that Joe's change will have to wait a while since it 
> includes make file changes that potentially interfere with changes for 
> the new build system. So, hopefully you get to push this first :)

Thanks. I've been watching the progress that Joe's change has been 
making. I guess you can think of this change as the one for hs24 and 
another with the SERIALGC changed appropriately being for hs25. :)



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