RFR: 8255984: Shenandoah: "adaptive" heuristic is prone to missing load spikes

[Aleksey Shipilev]

On Wed, 11 Nov 2020 08:14:40 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> This change adds a "reactive" heuristic for triggering concurrent GC cycles.
>> 
>> The reactive heuristic maintains a margin of error and an allocation spike detection mechanism to trigger cycles somewhat more aggressively than the 'adaptive' heuristic. This heuristic 'reacts' to the outcome of GC cycles by adjusting the sensitivity of the triggers.
>> 
>> JBS ticket is here: https://bugs.openjdk.java.net/browse/JDK-8255984
>> 
>> The "adaptive" heuristic remains the default.
>> 
>> Steps to reproduce and test will follow shortly (there are no new jtreg test failures for Shenandoah with this change).
>
> Thanks for updates. I would like to dive in with some testing. Second read nits below, meanwhile.

Oh, and change PR title to "8255984: Shenandoah: "adaptive" heuristic is prone to missing load spikes", so that bots know what issue it refers to.

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

PR: https://git.openjdk.java.net/jdk/pull/1099