RFR: 8373225: GenShen: More adaptive old-generation growth heuristics [v2]

[Kelvin Nilsen]

> When old-gen consumes a small percentage of heap size, trigger when old-gen expands by more than ShenandoahMinOldGenGrowthPercent, with default value 50%, from the live data in old at time of previous old-gen mark.
> 
> When old-gen consumes a larger percentage of heap size, we trigger when old-gen expands by more than  ShenandoahMinOldGenGrowthRemainingHeapPercent, with default value 25%, of the memory not live in old at the last marking of old.

Kelvin Nilsen has updated the pull request incrementally with three additional commits since the last revision:

 - Add comment to describe behavior of adjust_old_garbage_threshold()
 - Simplify representation of growth percentages
 - Change default value of ShenandoahMinOldGenGrowthRemainingHeapPercent

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Changes:
  - all: https://git.openjdk.org/jdk/pull/28561/files
  - new: https://git.openjdk.org/jdk/pull/28561/files/3c9a86ee..d5e4072d

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=28561&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=28561&range=00-01

  Stats: 39 lines in 4 files changed: 14 ins; 4 del; 21 mod
  Patch: https://git.openjdk.org/jdk/pull/28561.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28561/head:pull/28561

PR: https://git.openjdk.org/jdk/pull/28561