RFR: 8270100: Fix some inaccurate GC logging

[Albert Mingkun Yang]

On Thu, 8 Jul 2021 15:19:01 GMT, Volker Simonis <simonis at openjdk.org> wrote:

> If running with `-Xlog:gc+heap*=trace` the JVM will print the extra per thread amount which is added to the new generation on resize:
> 
> [0,105s][debug][gc,ergo,heap ] GC(0) New generation size 34112K->34176K [eden=27392K,survivor=3392K]
> [0,105s][trace][gc,ergo,heap ] GC(0) [allowed 0K extra for 0 threads]
> 
> Currently this will always print "0K extra for 0 threads" no matter how much extra space was added.
> 
> Also, the shrink factor will always be printed to be 0%, even if we run with `-XX:-ShrinkHeapInSteps` which pins the shrink factor at 100%:
> 
> [13,213s][trace][gc,heap ] GC(34) shrink_bytes: 463564,0K current_shrink_factor: 0 new shrink factor: 0 _min_heap_delta_bytes: 192,0K
> [13,239s][trace][gc,heap ] GC(34) Shrinking tenured generation from 531852K to 68288K
> 
> 
> The fix is trivial.

Can you share the complete flags and the benchmark for easy reproducing? Somehow I can't reproduce the gc logs; the flags and the benchmark I used:

`java -XX:+UseSerialGC -Xms2g -Xmx2g  '-Xlog:gc,gc+heap*=trace:gc.log::filecount=0' -jar dacapo-9.12-MR1-bach.jar h2 -s huge -n 1`

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PR: https://git.openjdk.java.net/jdk/pull/4727