RFR: 8318190: GenShen: Be less aggressive with triggers for old-gen has expanded [v4]

[Kelvin Nilsen]

> This patch reduces the frequency of old-has-grown triggers in the case that old usage is smaller than a particular threshold percentage (default value 5%) of the total heap size.  In this case, old is triggered for growth no more frequently than once every N cycles, where N defaults to 50.

Kelvin Nilsen has updated the pull request incrementally with one additional commit since the last revision:

  Fix user instructions

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Changes:
  - all: https://git.openjdk.org/shenandoah/pull/341/files
  - new: https://git.openjdk.org/shenandoah/pull/341/files/e7747100..b4071011

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=shenandoah&pr=341&range=03
 - incr: https://webrevs.openjdk.org/?repo=shenandoah&pr=341&range=02-03

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/shenandoah/pull/341.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah.git pull/341/head:pull/341

PR: https://git.openjdk.org/shenandoah/pull/341