8369219: JNI::RegisterNatives causes a memory leak in CodeCache

[fandreuz]

I propose to amend nmethod::is_cold to let GC collect not-entrant native nmethod instances.

Passes tier1 and tier2 (fastdebug).

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Issue

• JDK-8369219: JNI::RegisterNatives causes a memory leak in CodeCache (Bug - P4)

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• 03: Full - Incremental (8ea13b6e)
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[dholmes-ora]

/label add hotspot-compiler

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The hotspot-compiler label was successfully added.

[dean-long]

So I guess we need to decide what to do about native wrappers that are still "in use", but are "cold" because they haven't been called in a while. The above change would keep them around forever. We could instead allow them to be cleaned up like regular nmethods.