RFR: 8366157: Clarify in man pages that only G1 and Parallel supports MaxGCPauseMillis [v3]

[Thomas Schatzl]

On Fri, 29 Aug 2025 09:29:10 GMT, Jonas Norlinder <duke at openjdk.org> wrote:

>> Hi all,
>> 
>> This patch clarifies the description of `MaxGCPauseMillis`.
>
> Jonas Norlinder has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Parallel do support a pause time target but does not use it by default

Changes requested by tschatzl (Reviewer).

src/java.base/share/man/java.md line 2507:

> 2505:     and Parallel supports a maximum GC pause time target. For G1, the default
> 2506:     maximum pause time target is 200 milliseconds. Parallel do not use a
> 2507:     pause time goal by default.

Suggestion:

    soft goal, and the JVM will make a best effort to achieve it. The default
    maximum pause time target is 200 milliseconds.
    Only G1 and Parallel GC support a maximum pause time target.


* grammar error: `supports`->`support`
* I do not think it is useful to tell that Parallel GC does not adhere to this target by default and needs another setting. First, this begs the question what option this is, and second, this information should be part of the tuning guide as otherwise the manpage will get too lengthy (if we explained all interactions with all flags for every option here). I am aware that most likely this is not currently in the documentation.
I mean, similarly to Parallel, one would, to be somewhat complete also detail that there is an important interaction with another flag (-XX:GCPauseIntervalMillis). (This is explained in the guide)
Leaving out this sentence is not a strong opinion, but just imho.

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

PR Review: https://git.openjdk.org/jdk/pull/26940#pullrequestreview-3168073800
PR Review Comment: https://git.openjdk.org/jdk/pull/26940#discussion_r2309688836