Integrated: 8373023: [REDO] Remove the default value of InitialRAMPercentage

[Joel Sikström]

On Wed, 3 Dec 2025 16:07:07 GMT, Joel Sikström <jsikstro at openjdk.org> wrote:

> Hello,
> 
> We backed out this change in https://github.com/openjdk/jdk/pull/28617 after issues in found in testing. Moving forward, we've decided to problem list a few tests that assumes that a GC does not run during their execution. When the initial heap size becomes very low with this change, it may trigger additional GCs, which may interfere with a few tests.
> 
> We are planning to follow up on the problem lists with test fixes in:
> https://github.com/openjdk/jdk/pull/28638, https://github.com/openjdk/jdk/pull/28637
> 
> From the original RFE: 
> 
> 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.
> 
> Testing:
> * Oracle's tier1-3

This pull request has now been integrated.

Changeset: 8d80778e
Author:    Joel Sikström <jsikstro at openjdk.org>
URL:       https://git.openjdk.org/jdk/commit/8d80778e05aee878f9a3e8beabe6a0cfd0a02c16
Stats:     15 lines in 5 files changed: 11 ins; 1 del; 3 mod

8373023: [REDO] Remove the default value of InitialRAMPercentage

Reviewed-by: stefank, sjohanss, aboldtch

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PR: https://git.openjdk.org/jdk/pull/28641