RFR: 8316929: Shenandoah: Shenandoah degenerated GC and full GC need to cleanup old OopMapCache entries

[Aleksey Shipilev]

On Tue, 26 Sep 2023 12:48:12 GMT, Zhengyu Gu <zgu at openjdk.org> wrote:

> During STW root scan, interpreted frame's oop map may be cached. But due to limited cache size (32 entries per instance class), entries may be evicted to old entries list due to collision, should be cleanup in VM_Operation's doit_epilogue(), or risk leaking memory.
> 
> Test:
>   hotspot_gc_shenandoah (fastdebug and release on MacOSX)

This looks okay, but I think you can "just" add `OMC::cleanup_old_entries` in `VM_ShenandoahReferenceOperation` destructor, without introducing the intermediary?

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PR Review: https://git.openjdk.org/jdk/pull/15921#pullrequestreview-1652325437