RFR: 8297718: Make NMT free:ing protocol more granular [v2]

[Johan Sjölen]

On Thu, 8 Dec 2022 02:34:07 GMT, David Holmes <dholmes at openjdk.org> wrote:

>> src/hotspot/share/runtime/os.cpp line 732:
>> 
>>> 730:       // We have however marked it as dead, revert this change.
>>> 731:       header->revive();
>>> 732:       return nullptr;
>> 
>> This is the very first usage of `nullptr` instead of `NULL`, and we now have a mix of both.
>> 
>> Was this a deliberate choice? Should we then switch all `NULLs` to `nullptr` in here?
>
> We should try to use `nullptr` in new code and change from NULL within those methods for consistency, but a broader cleanup should be done as a separate cleanup RFE.

My strategy for the `NULL` to `nullptr` conversion is that if I touch the line of code, I change it to `nullptr`. Changing whole methods lead to a larger diff for reviewers, which can be annoying when looking for the relevant changes.

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PR: https://git.openjdk.org/jdk/pull/11390