RFR: 8366434: THP not working properly with G1 after JDK-8345655

[Aleksey Shipilev]

On Tue, 2 Sep 2025 16:59:50 GMT, Stefan Johansson <sjohanss at openjdk.org> wrote:

>> test/hotspot/jtreg/gc/TestTransparentHugePagesHeap.java line 105:
>> 
>>> 103: 
>>> 104:             final Pattern heapSection = Pattern.compile("^" + heapAddress + ".*");
>>> 105:             final Pattern thpEligible = Pattern.compile("THPeligible:\\s+(\\d)\\s*");
>> 
>> I thought we had the `smaps` parser somewhere, and here it is: https://github.com/openjdk/jdk/blob/444a8fa14e8ab016b8aae018054c5dc1eb843fee/test/hotspot/jtreg/runtime/os/TestTracePageSizes.java#L149 -- maybe yank it from there to some testlib location, and use it?
>
> I agree that this is what we want long-term, we talked about this internally as well. At one point we also just extended the `TestTracePageSizes.java` test to ensure THP for the heap to avoid some duplication. In the end we felt creating a new test was the best approach right now, to also allow for small and safe backport to 25u.
> 
> Created [JDK-8366716](https://bugs.openjdk.org/browse/JDK-8366716) to keep track of this. 
> 
> Are you good with this approach?

Yes, OK.

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PR Review Comment: https://git.openjdk.org/jdk/pull/27051#discussion_r2316739575