RFR: 8376051: gc/stress/TestStressG1Uncommit.java fails assertLessThan: expected that xxx < xxx

[Thomas Schatzl]

On Thu, 22 Jan 2026 08:57:03 GMT, SendaoYan <syan at openjdk.org> wrote:

> > It will re-evaluate and resize the heap at every young gc, based on GC cpu usage.
> 
> What I meant is the free heap memory ratio will never greater than 100%, so when the value of MaxHeapFreeRatio is seted to 100, G1 will never give back memory to OS? I am not familiar with GC.

These ratios (actually percentages) only every applied to full gcs, and only for Serial/Parallel/G1 and maybe Shenandoah.

Since JDK 26, G1 will re-evaluate the "best" heap size based on GC cpu usage. So if lots of time, more than the goal, `GCTimeRatio`, is spent in GC activity, G1 will shrink the heap and give back memory to the OS. (Actually, in many applications, G1 is keeping a smaller footprint now).

G1 will re-evaluate and shrink/expand at every young gc (https://bugs.openjdk.org/browse/JDK-8238687), not only full gc/System.gc() based on arbitrary Min/MaxHeapFreeRatio. The [CSR](https://bugs.openjdk.org/browse/JDK-8375300) for the change causing this test failure hopefully explains the reason for this change well enough.

Actually we are not sure how/why this test failure slipped through.

> >    I think revert the WhiteBox change also acceptable. Should I do that?
> Yes, I think System.gc() is still cleaner.

In this case, `System.gc()` and `WhiteBox.fullGC()` act exactly the same so I would also keep `System.gc()` just to keep the code simpler.

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PR Comment: https://git.openjdk.org/jdk/pull/29357#issuecomment-3783709625