RFR: 8370527: Memory leak after 8316694: Implement relocation of nmethod within CodeCache [v2]

[Vladimir Kozlov]

On Wed, 29 Oct 2025 14:56:14 GMT, Leonid Mesnik <lmesnik at openjdk.org> wrote:

>>> Ah, so _there_! I confused myself. This one is readable: the counter `0` means we can free. It would be even better if you did `inc_immutable_data_refcount()` and `dec_immutable_data_refcount()`, and did e.g.:
>>> 
>>> ```
>>> if (dec_immutable_data_refcount() == 0) {
>>>   os::free(_immutable_data);
>>> }
>>> 
>>> int dec_immutable_data_refcount() {
>>>   int refcount = get(...);
>>>   assert(refcount > 0, "Must be positive");
>>>   set(refcount - 1);
>>>   return refcount - 1;
>>> }
>>> ```
>>> 
>>> Because the next thing you know this would need to be replaced with Atomics a year later.
>> 
>> I agree this makes the code cleaner.
>> 
>> I replaced the getter and setter for the counter with `init_immutable_data_ref_count`, `inc_immutable_data_ref_count`, and `dec_immutable_data_ref_count`. I also shortened the counter name from `immutable_data_references_counter` to `immutable_data_ref_count`
>> 
>> I modified `NMethod.java` to calculate the offsets that same way as is done in the JVM. I missed this in [JDK-8369642](https://bugs.openjdk.org/browse/JDK-8369642)
>> 
>> The last notable change is that I modified the [immutable data size calculation](https://github.com/chadrako/jdk/blob/26bdc3ceb4ab9ad9cb9a4218bb87ce2d7546fa22/src/hotspot/share/code/nmethod.cpp#L1155) to only include a reference counter if there is immutable data
>
> @chadrako The testing pass now.

@lmesnik please add link to testing in confidential comment in JBS

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PR Comment: https://git.openjdk.org/jdk/pull/28008#issuecomment-3462693312