RFR: 8366241: NMT: Consolidate [Virtual/Committed/Reserved]Regions into one structure [v6]

[Afshin Zafari]

On Thu, 20 Nov 2025 13:01:45 GMT, Paul Hübner <phubner at openjdk.org> wrote:

>> Afshin Zafari has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains nine commits:
>> 
>>  - Merge remote-tracking branch 'origin/master' into _8366241_nmt_consolidate_structures
>>  - fixes
>>  - Merge remote-tracking branch 'origin/master' into _8366241_nmt_consolidate_structures
>>  - Merge remote-tracking branch 'origin/master' into _8366241_nmt_consolidate_structures
>>  - master merge fix
>>  - Merge remote-tracking branch 'origin/master' into _8366241_nmt_consolidate_structures
>>  - after merge with 8366363.
>>  - Merge remote-tracking branch 'origin/master' into _8366241_nmt_consolidate_structures
>>  - 8366241: NMT: Consolidate [Virtual/Committed/Reserved]Regions into one structure
>
> src/hotspot/share/nmt/virtualMemoryTracker.hpp line 271:
> 
>> 269:   inline const NativeCallStack* committed_call_stack() const         { return &_committed_stack; }
>> 270: 
>> 271:   bool is_valid() const { return base() != nullptr && size() != 0;}
> 
> The old structures had the base address and size by default initialised to 1. I think the new "invalid" values of 0 and 0 are more ergonomic, but I'm wondering, what's the reason we used 1 originally?

IIRC, they were used for debugging  and tracing some cases that happened during VMATree implementation.

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PR Review Comment: https://git.openjdk.org/jdk/pull/27137#discussion_r2559312713