8236073: G1: Use SoftMaxHeapSize to guide GC heuristics

[tschatzl]

Hi all,

please review this change to implement SoftMaxHeapSize for G1.

Main change is that SoftMaxHeapSize now impacts the G1IHOPControl::target_occupancy(), i.e. the amount of bytes G1 when reclaim should start.

Most of the other changes are just about updating logging/JFR and making sure that the SoftMaxHeapSize values are consistent across calls.

Testing: tier1-5

Thanks,
Thomas

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Progress

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Warnings

 ⚠️ Patch contains a binary file (src/java.base/share/classes/jdk/internal/icu/impl/data/icudt76b/nfc.nrm)
 ⚠️ Patch contains a binary file (src/java.base/share/classes/jdk/internal/icu/impl/data/icudt76b/ubidi.icu)
 ⚠️ Patch contains a binary file (src/java.base/share/classes/jdk/internal/icu/impl/data/icudt76b/uprops.icu)
 ⚠️ Patch contains a binary file (test/jdk/javax/net/ssl/HttpsURLConnection/crisubn.jks)
 ⚠️ Patch contains a binary file (test/jdk/javax/net/ssl/HttpsURLConnection/trusted.jks)

Issue

• JDK-8236073: G1: Use SoftMaxHeapSize to guide GC heuristics (Enhancement - P4)

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[caoman]

Responding to @tschatzl's comment in https://bugs.openjdk.org/browse/JDK-8236073:

SoftMaxHeapSize just affects the target heap size for scheduling concurrent marks. GCTimeRatio sets the target as well, so the result is basically MIN(SoftMaxHeapSize, GCTimeRatio-based-target).

I have not verified, but could this problematic feedback loop happen?
User sets a low SoftMaxHeapSize value, then G1 starts to trigger more concurrent marks and incremental collections, then GC overhead becomes higher. Then G1 observes that the actual GC overhead is above the GCTimeRatio target, so it expands the heap. Thus, setting a small SoftMaxHeapSize makes G1 expand the heap further,

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