RFR: JDK-8262068: Improve G1 Full GC by skipping compaction for regions with high survival ratio [v14]

[Thomas Schatzl]

On Fri, 9 Apr 2021 10:49:11 GMT, Thomas Schatzl <tschatzl at openjdk.org> wrote:

>> Thanks for discussion! I had the same concern (BOTs of these Survivor-turned-to-Old regions contains no useful info, so might make it very slow when finding block start in these regions), but I was not sure if there is some "lazy" mechanism to fill valid BOTs info for these regions when they are accessed subsequently. I just not have time to do further investigation, now I got the answer from you. 
>> 
>> Sure I will add code to fill valid BOTs info for these young regions by the end of full gc.
>> I'm not sure if it's OK for me to do this BOTs filling action in a separate issue? As we already had such a long discussion, I think it's might be better for us to initialize another discussion for this specific follow-up issue. Please kindly let me know your thoughts.
>
> It is fine with me to fix this separately.
> 
> There is some lazy mechanism to fill this BOT, but it does not work in this case (which is the gist of what I said above).

Note that if that were fixed, I think PR #3356 would not be needed - because then young region BOTs have the expected contents :) Your call.

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PR: https://git.openjdk.java.net/jdk/pull/2760