RFR: 8337217: Port VirtualMemoryTracker to use VMATree [v34]

[Johan Sjölen]

On Tue, 4 Mar 2025 11:20:05 GMT, Afshin Zafari <azafari at openjdk.org> wrote:

>> - `VMATree` is used instead of `SortedLinkList` in new class `VirtualMemoryTracker`.
>>  -  A wrapper/helper `RegionTree` is made around VMATree to make some calls easier.
>>  - `find_reserved_region()` is used in 4 cases, it will be removed in further PRs.
>>  - All tier1 tests pass except this https://bugs.openjdk.org/browse/JDK-8335167.
>
> Afshin Zafari has updated the pull request incrementally with one additional commit since the last revision:
> 
>   test cases for doing reserve or commit the same region twice.

Still working through the files, a few more comments.

src/hotspot/share/nmt/memReporter.cpp line 451:

> 449:     });
> 450: 
> 451:     if (reserved_and_committed)

Missing braces

src/hotspot/share/nmt/regionsTree.hpp line 37:

> 35: // for processing the tree nodes in a shorter and more meaningful way.
> 36: class RegionsTree : public VMATree {
> 37:  private:

Remote private, not needed.

src/hotspot/share/nmt/regionsTree.hpp line 56:

> 54:       NodeHelper() : _node(nullptr) { }
> 55:       NodeHelper(Node* node) : _node(node) { }
> 56:       inline bool is_valid() { return _node != nullptr; }

Missing `const`

src/hotspot/share/nmt/regionsTree.inline.hpp line 33:

> 31: void RegionsTree::visit_committed_regions(const ReservedMemoryRegion& rgn, F func) {
> 32:   position start = (position)rgn.base();
> 33:   size_t end = (size_t)rgn.end() + 1;

Can we `static_cast<size_t>(rgn.end())` instead?

src/hotspot/share/nmt/virtualMemoryTracker.cpp line 60:

> 58:     if (tracker == nullptr) return false;
> 59:     _tracker = new (tracker) VirtualMemoryTracker(level == NMT_detail);
> 60:     return _tracker->tree() != nullptr;

@afshin-zafari , `_tracker->tree()` can never be null anymore. In the future we should do a PR where we change it to return a reference.

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PR Review: https://git.openjdk.org/jdk/pull/20425#pullrequestreview-2661644343
PR Review Comment: https://git.openjdk.org/jdk/pull/20425#discussion_r1981728394
PR Review Comment: https://git.openjdk.org/jdk/pull/20425#discussion_r1981743711
PR Review Comment: https://git.openjdk.org/jdk/pull/20425#discussion_r1981745212
PR Review Comment: https://git.openjdk.org/jdk/pull/20425#discussion_r1981747136
PR Review Comment: https://git.openjdk.org/jdk/pull/20425#discussion_r1981755525