RFR: 8290177: Improve documentation in G1MMUTracker [v3]

[Thomas Schatzl]

> Hi all,
> 
>   please review this change to improve the naming and documentation in `G1MMUTracker::when_sec`. Recently we have been looking at some young gen sizing issues (for another time), and it took some time to understand what the code does and how it works. This is kind of the result of this internal discussion, but I'm open to improve this further.
> 
> Testing: gha
> 
> Thanks,
>   Thomas

Thomas Schatzl has updated the pull request incrementally with one additional commit since the last revision:

  current_timestamp vs. timestamp

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/9471/files
  - new: https://git.openjdk.org/jdk/pull/9471/files/54d89bbd..dfafe00b

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=9471&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=9471&range=01-02

  Stats: 2 lines in 2 files changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/9471.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9471/head:pull/9471

PR: https://git.openjdk.org/jdk/pull/9471