RFC: JEP draft: Automatic Heap Sizing for G1

[Kirk Pepperdine]

Hi Thomas,

I like the proposal. The only questions I have is with regards to the section on "Responding to machine memory pressure” and testing. How do you see testing the features that respond to increased memory pressure?

Kind regards,
Kirk


> On Jun 26, 2025, at 12:45 AM, Thomas Schatzl <thomas.schatzl at oracle.com> wrote:
> 
> Hi all,
> 
>  with this email I would like to collect feedback for the "Automatic Heap Sizing for G1" JEP draft I started writing recently [0].
> 
> The purpose of this JEP is to have G1 automatically and dynamically adapt the maximum heap size according to the environment.
> 
> We think there is fair possibility to complete the implementation by next JDK's feature complete date as the main preparatory change [1] is currently under review (fwiw, please chime in if interested, more feedback is always appreciated).
> 
> G1 AHS is somewhat different to ZGC's Automatic Heap Sizing proposal as part of the functionality proposed there has already been available in G1 for a long time.
> 
> It should be fairly complete, although I'm still a bit conflicted about the usefulness of the proposed G1GCIntensity flag, but we can always change that area as needed.
> 
> Thanks,
>  Thomas
> 
> [0] https://bugs.openjdk.org/browse/JDK-8359211
> [1] https://bugs.openjdk.org/browse/JDK-8238687 / https://git.openjdk.org/jdk/pull/25832
>