8354727: CompilationPolicy creates too many compiler threads when code cache space is scarce

[mhaessig]

Issue Summary

Running

java -XX:+SegmentedCodeCache -XX:ReservedCodeCacheSize=10M -XX:NonNMethodCodeHeapSize=6M \
     -XX:ProfiledCodeHeapSize=5M -XX:NonProfiledCodeHeapSize=5M -version

on a machine with more than 255 cores, this would fail with the message that the specified NonNMethodCodeHeapSize is too small to fit all compiler buffers (instead of failing because the sum of the heaps is larger than the ReservedCodeCacheSize). Hence, the calculated compiler count is too high. This is due to CompilationPolicy::initialize() checking how many compiler buffers fit into the ReservedCodeCacheSize. However, in the case above, this is significantly larger than NonNMethodCodeHeapSize and causes a check updated in #17244 to fail that should ensure that NonNMethodCodeHeapSize is at least CodeCacheMinimumUseSpace plus the size of all CICompilerCount compiler buffers. This is stronger than before #17244 where this check merely required NonNMethodCodeHeapSize >= CodeCacheMinimumUseSpace due to the fact that compiler buffers can also use the rest of the code cache if the non-nmethod heap is not sufficient.

Change Rationale

This PR reverts the failing check to ensuring NonNMethodCodeHeapSize >= CodeCacheMinimumUseSpace since the computation of the ergonomic CICompilerCount in CompilationPolicy::initialize() does not support the assumption that all compiler buffers must always fit inside the non-nmethod code heap.

This change required to adjust a test, because with the weaker check, it is currently not possible to trigger it from the commandline.

Testing

• Github Actions
• tier1 and tier2 plus some Oracle internal testing

---

Progress

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Issue

• JDK-8354727: CompilationPolicy creates too many compiler threads when code cache space is scarce (Bug - P4)

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