RFR: 8241670: Enhance heap region size ergonomics to improve OOTB performance

[Claes Redestad]

Hi,

looks great - both the patch and the out-of-the-box performance
improvements.

Thanks!

/Claes

On 2020-03-31 11:42, Stefan Johansson wrote:
> Hi,
> 
> Please review this enhancement to improve the out of the box performance 
> of G1.
> 
> Webrev: http://cr.openjdk.java.net/~sjohanss/8241670/00/index.html
> JBS: https://bugs.openjdk.java.net/browse/JDK-8241670
> 
> Summary
> The default heap region size determined at startup used the initial and 
> max heap size to calculate a region size so that the heap would have at 
> least 2048 regions (if possible). This proposed patch will change this to:
> 1) Only consider Max to make it easy to explain and avoid strange 
> situations where -Xms or the lack of it will cause different region size 
> for the same max heap size.
> 2) Round up the region size to next power of 2, since we've seen many 
> cases where a larger region size is beneficial.
> 3) Keep the 2048 target for now since the other two changes, will have 
> good effect on choosing a larger region size for heaps above 2G.
> 
> Testing
> Mach5 tier1-4, aurora performance run for sanity and manual performance 
> testing to verify results.
> 
> Thanks,
> Stefan