RFR: JDK-8262068: Improve G1 Full GC by skipping compaction for regions with high survival ratio [v11]

[Stefan Johansson]

On Fri, 26 Mar 2021 09:56:13 GMT, Hamlin Li <mli at openjdk.org> wrote:

>> Looks pretty good actually.
>
> I think it's better to agree on one thing first: 
> 1. Thomas suggests to use attribute table to store the pinned info for "high survival ratio regions"
> 2. Stefan suggests to add a new Region Type.
> I'm OK with both ways, "new Region Type" way is a little bit redudant but it's more straight.
> Would you mind to share comments on this point?

As I responded to Thomas comment, I'm fine with just using the attribute table, as long as we structure the code a bit better. Like using a `should_compact()` function that checks both `hr->is_pinned()` and the liveness.

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PR: https://git.openjdk.java.net/jdk/pull/2760