[jdk11u-dev] RFR: 8228609: G1 copy cost prediction uses used vs. actual copied bytes [v6]

[Yude Lin]

On Sat, 2 Apr 2022 06:02:19 GMT, Yude Lin <duke at openjdk.java.net> wrote:

>> I would like to backport 8228609 which fixes a prediction error regarding cost per bytes copied.
>> 
>> The patch does not apply cleanly, so this backport is basically changing the calculation of copied bytes.
>> 
>> https://bugs.openjdk.java.net/browse/JDK-8227442 is not in 11u. So this patch also uses G1ParScanThreadState::surviving_young_words() in place of _surviving_young_words to adjust for the correct cset index.
>
> Yude Lin has updated the pull request incrementally with one additional commit since the last revision:
> 
>   trigger GitHub actions

Gentle ping. Can anyone review this?

The reason I believe it's worth a backport is, apart from what's mentioned in https://bugs.openjdk.java.net/browse/JDK-8228609, it correctly accounts for early reclaimed humongous objects. I think originally the oversight of the size of early reclaimed humongous objects cause the calculation to be erroneous, resulting in a very high copy time prediction and unstable gc frequency.

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PR: https://git.openjdk.java.net/jdk11u-dev/pull/927