8236073: G1: Use SoftMaxHeapSize to guide GC heuristics

[caoman]

Hi all,

I have implemented SoftMaxHeapSize for G1 as attached. It is completely reworked compared to previous PR, and excludes code for CurrentMaxHeapSize. I believe I have addressed all direct concerns from previous email thread, such as:

• does not respect MinHeapSize;
• being too "blunt" and does not respect other G1 heuristics and flags for resizing, such as MinHeapFreeRatio, MaxHeapFreeRatio;
• does not affect heuristcs to trigger a concurrent cycle;

This recent thread also has some context.

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Issue

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

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[bridgekeeper]

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[openjdk]

@caoman The following label will be automatically applied to this pull request:

• hotspot-gc

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[mlbridge]

Webrevs

• 01: Full - Incremental (59d1ac69)
• 00: Full (b4293e4e)

[caoman]

@mo-beck Here is my implementation for SoftMaxHeapSize for G1. Let me know if you have any feedback or concerns.

[caoman]

This probably requires fixing https://bugs.openjdk.org/browse/JDK-8352765 before users try to use SoftMaxHeapSize. Otherwise, setting a small SoftMaxHeapSize could trigger premature OutOfMemoryError.