RFR: 8317755: G1: Periodic GC interval should test for the last whole heap GC [v2]

[Y. Srinivas Ramakrishna]

On Wed, 18 Oct 2023 14:27:26 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> See the description in the bug. Fortunately, we already track the last whole-heap GC. The new regression test verifies the behavior.
>> 
>> Additional testing:
>>  - [x] Linux x86_64 fastdebug `tier1 tier2 tier3`
>
> Aleksey Shipilev has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains five additional commits since the last revision:
> 
>  - Merge branch 'master' into JDK-8317755-g1-periodic-whole
>  - Optional flag
>  - Merge branch 'master' into JDK-8317755-g1-periodic-whole
>  - Keep the cast
>  - Fix

LGTM. Very useful when there is no direct feedback loop from resource pressure that we might otherwise have used for signaling the need for a whole heap GC, so is a good escape hatch to put in the hands of service owners. Of course, like any escape hatch, it could be misused, but I don't think that is a concern about ejection seats from fighter jets for example. We trust those who fly the jets not to eject for no reason.

I would suggest formally dissociating this from the JEP itself. The fix ups to the JEP's and its implementation shortcomings can be addressed fully in the fullness of time. My USD 0.02.

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Marked as reviewed by ysr (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/16107#pullrequestreview-1751328467