RFR: 8373225: GenShen: More adaptive old-generation growth heuristics [v4]

[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 one additional commit since the last revision:

  Protect against underflow when computing old growth trigger threshold

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Changes:
  - all: https://git.openjdk.org/jdk/pull/28561/files
  - new: https://git.openjdk.org/jdk/pull/28561/files/c7c22974..79a21ee6

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=28561&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=28561&range=02-03

  Stats: 10 lines in 1 file changed: 7 ins; 0 del; 3 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