RFR: 8371986: Remove the default value of InitialRAMPercentage

[Joel Sikström]

On Thu, 27 Nov 2025 13:27:00 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> 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.
>
> Marked as reviewed by shade (Reviewer).

Thank you for the reviews! @shipilev @xmas92

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PR Comment: https://git.openjdk.org/jdk/pull/28530#issuecomment-3601818460