[crac] RFR: 8353241: [CRaC] Support ZGC [v3]

[Radim Vansa]

On Mon, 14 Apr 2025 06:57:19 GMT, Timofei Pushkin <tpushkin at openjdk.org> wrote:

>> Radim Vansa has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains three commits:
>> 
>>  - Merge branch 'crac' into zgc
>>  - fixup
>>  - 8353241: CRaC ZGC support
>
> src/hotspot/share/gc/z/zPageAllocator.hpp line 173:
> 
>> 171:   void threads_do(ThreadClosure* tc) const;
>> 172: 
>> 173:   void cleanup_unused();
> 
> This should not be addressed in this PR, but I find "cleanup_unused" name pretty undescriptive, both here and in `CollectedHeap` in general. It wasn't obvious to me that this is something used only by CRaC. I would propose `cleanup_before_checkpoint`, for example.

The name is not mandated by any interface so I can rename it even here...

> src/hotspot/share/runtime/crac.cpp line 429:
> 
>> 427:     MemTracker::final_report(tty);
>> 428:   }
>> 429: 
> 
> Is this left intentionally? If yes, I think nothing will be printed after this on the real VM exit (after restore) since there is `Atomic::cmpxchg(&g_final_report_did_run, false, true) == false` in `MemTracker::final_report()`.

Yes, I've left this intentionally. Well spotted, I'll make sure that the final report will run as well.

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PR Review Comment: https://git.openjdk.org/crac/pull/219#discussion_r2042020387
PR Review Comment: https://git.openjdk.org/crac/pull/219#discussion_r2041549347