RFR: 8276098: Do precise BOT updates in G1 evacuation phase

[Stefan Johansson]

On Mon, 1 Nov 2021 06:31:18 GMT, Yude Lin <duke at openjdk.java.net> wrote:

> Another thought is maybe `G1BlockOffsetTable::set_offset_array/_raw` don't need to be conservatively ordered, that is, they can be memory_order_relaxed. Since now all updates are in the pause and there is no concurrent readers.

Another good point. I think such change should also be done as a separate PR and we should probably also look at hardening the code to not allow updates because the BOT is not precise (because it should be). I will file issues for these two things.

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PR: https://git.openjdk.java.net/jdk/pull/6166