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

[Thomas Schatzl]

Hi,

On 31.03.20 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.
> 

- heapRegion.cpp: s/benificial/beneficial

- heapRegionBounds.hpp: Maybe remove the "(based on the max heap size)." 
comment part. Apparently we forgot to update that last time, so we 
probably will next time too. The code is simple enough too.

- maybe update copyrights while you are at it.

No need to re-review these comment updates.

Looks good.

Thanks,
   Thomas