RFR: 8267894: Skip work for empty regions in G1 Full GC

[Stefan Johansson]

On Tue, 17 Aug 2021 13:29:59 GMT, Ivan Walulya <iwalulya at openjdk.org> wrote:

> Hi all,
> 
> Please review this change to skip doing work on regions that were empty at the beginning of the Full GC in phases that execute on a per-region basis.
> 
> Testing: Tier 1-3.

I think the text "not initialized yet" is a bit wrong. We should never call is_skip_marking() for objects in "Invalid" regions, because there can't be any objects there. Same goes for "Free" regions. So I would change the assert to something like: 

assert(!is_free(obj), "Should be no objects in free regions."); 

I agree that changing the default value should work. One benefit of using a new state could be to have a difference between free and not committed regions. But not sure it is worth the effort right now.

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PR: https://git.openjdk.java.net/jdk/pull/5143