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

[Afshin Zafari]

On Mon, 3 Mar 2025 19:58:16 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 72:
> 
>> 70:   EXPECT_EQ(rmr.base(), (address)1400);
>> 71:   rmr = rt.find_reserved_region((address)1005);
>> 72:   EXPECT_EQ(rmr.base(), (address)1000);
> 
> When I do:
> 
>   rmr = rt.find_reserved_region((address)999);
> 
> I get back ReservedMemoryRegion with base == 1, I am not 100% sure what I was expecting - probably 0, but not 1.

Here, the 999 address is not in any region. 
If no region is found by the `rt.find_reserved_region(addr)`, a region with base==1 and size==1 is returned. base == 0 triggers some assertions since it is a pointer. Because of this, I added the `ReservedMemoryRegion::is_valid()` which checks base and size.


rmr = rt.find_reserved_region(999);
if (!rmr.is_valid()) {
  // your code ....
}

P.S.: The `find_reserved_region` is expensive and hopefully it would be removed in future PRs.

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

PR Review Comment: https://git.openjdk.org/jdk/pull/20425#discussion_r1979067689