RFR: Clear cards for old regions when they are put into service

[Kelvin Nilsen]

On Wed, 23 Feb 2022 21:54:27 GMT, William Kemper <wkemper at openjdk.org> wrote:

> Preemptively clearing cards during recycle for every region adds considerable overhead to the concurrent clean up phase. Moving card clearing transfers the cost of card clearing to the evacuation phase and reduces the cost to only those regions that will be used by the old generation.

Marked as reviewed by kdnilsen (Committer).

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PR: https://git.openjdk.java.net/shenandoah/pull/119