RFR: 8341042: GenShen: Reset mark bitmaps for unaffiliated regions when preparing for a cycle

[William Kemper]

On Thu, 26 Sep 2024 16:55:55 GMT, William Kemper <wkemper at openjdk.org> wrote:

> A recent change to reset unaffiliated bitmaps during the concurrent cleanup phase has caused a performance regression. Likely because concurrent cleanup only uses one thread (at this time). This issue is to revert the regression causing change while we work on a preferred solution.

src/hotspot/share/gc/shenandoah/shenandoahHeapRegion.cpp line 582:

> 580:   set_top(bottom());
> 581:   clear_live_data();
> 582:   heap->marking_context()->clear_bitmap(this);

This is a merge error on this branch. `shenandoah-jdk21u` does not reset the bitmaps twice like this.

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PR Review Comment: https://git.openjdk.org/shenandoah/pull/504#discussion_r1777458359