RFR: 8337217: Port VirtualMemoryTracker to use VMATree [v33]

[Johan Sjölen]

On Mon, 3 Mar 2025 20:17:15 GMT, Gerard Ziemski <gziemski at openjdk.org> wrote:

>> Afshin Zafari has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   style, some cleanup, VMT and regionsTree circular dep resolved
>
> test/hotspot/gtest/nmt/test_regions_tree.cpp line 98:
> 
>> 96:   rt.reserve_mapping(1400, 50, rd);
>> 97: 
>> 98:   rt.commit_region((address)1010, 5UL, ncs);
> 
> What would, what should happen if we repeat the same reserve_mapping?
> 
> rt.commit_region((address)1010, 5UL, ncs);
> rt.commit_region((address)1010, 5UL, ncs);
> 
> Are/should we be allowed to do this?

Nothing would happen, the state of the tree would stay the same. We should allow it, at least on product builds! For me, the most important part of this rewrite is getting rid of NMT crashing because it reaches states that it can't do anything with. We can handle more usage patterns, and we try our darnest to not fail.

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PR Review Comment: https://git.openjdk.org/jdk/pull/20425#discussion_r1978986884