RFR: 8371986: Remove the default value of InitialRAMPercentage

[Joel Sikström]

Hello,

This RFE changes the default of `InitialRAMPercentage` to 0, effectively removing its default value. Please see the CSR for specific details on this change.

Changing the default value to 0 results in the behavior that the initial heap size (InitialHeapSize) is set to the minimum heap size (MinHeapSize). This is because of the following lines in `Arguments::set_heap_size()`, which takes the MAX value of MinHeapSize as well:

uint64_t initial_memory = (uint64_t)(((double)MaxRAM * InitialRAMPercentage) / 100);
...

reasonable_initial = MAX3(reasonable_initial, reasonable_minimum, MinHeapSize);
reasonable_initial = MIN2(reasonable_initial, MaxHeapSize);


This change improves startup performance for all GCs, but affects the time-to-peak performance in some out-of-the-box configurations for some GCs. This is mainly visible in ParallelGC.

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Commit messages:
 - 8371986: Remove the default value of InitialRAMPercentage

Changes: https://git.openjdk.org/jdk/pull/28530/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28530&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8371986
  Stats: 4 lines in 3 files changed: 0 ins; 1 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/28530.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28530/head:pull/28530

PR: https://git.openjdk.org/jdk/pull/28530