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

[Gerard Ziemski]

On Thu, 1 Dec 2022 13:59:25 GMT, Johan Sjölen <jsjolen at openjdk.org> wrote:

>> This PR avoids the double registration of a failed `os::realloc` in NMT by doing the NMT free protocol steps inline (asserting block integrity, marking of MallocHeader, and registrering results to statistics). This is done by creating a new struct `FreePackage` which includes all of the necessary data for registrering results.
>> 
>> I also did some light refactoring which I think makes the protocol clearer, these are done piece wise as separate commits for the reviewers' convenience.
>
> Johan Sjölen has updated the pull request incrementally with 10 additional commits since the last revision:
> 
>  - Add test that asserts block integrity after revival
>  - Make MallocHeader NONCOPYABLE
>  - Rest of it
>  - Adjust comments
>  - Put back comment, suitably rewritten
>  - Note reversibility of mark_block_as_dead
>  - Rename record_free_block to record_free
>  - Rename record_free to deaccount
>  - Move FreePackage into MallocHeader and rename
>  - Rename as revive, delete copy ctr

Marked as reviewed by gziemski (Committer).

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?

-------------

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