RFR: 8320370: NMT: Change MallocMemorySnapshot to simplify code.

[Thomas Stuefe]

On Sat, 18 Nov 2023 15:48:19 GMT, Johan Sjölen <jsjolen at openjdk.org> wrote:

> Hi,
> 
> `MallocMemorySnapshot` used to be initialized in a quite non-standard way, using global placement new on an array of `size_t` of the size required to fit `MallocMemorySnapshot`. This looks like it was intended to circumvent some `ResourceObj` internals, but I'm unsure of its purpose. This change does what you expect a regular initialization of a global variable to look like.
> 
> ~Currently running through tier1.~ GHA passed and so did tier1 on Oracle CI.

Looks good, smaller nits.

src/hotspot/share/nmt/mallocTracker.cpp line 46:

> 44: #include "utilities/vmError.hpp"
> 45: 
> 46: MallocMemorySnapshot MallocMemorySummary::_snapshot{};

Why the curly braces?

src/hotspot/share/nmt/virtualMemoryTracker.cpp line 52:

> 50: 
> 51: void VirtualMemorySummary::initialize() {
> 52: }

Can be removed.

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PR Review: https://git.openjdk.org/jdk/pull/16724#pullrequestreview-1739716823
PR Review Comment: https://git.openjdk.org/jdk/pull/16724#discussion_r1399144474
PR Review Comment: https://git.openjdk.org/jdk/pull/16724#discussion_r1399147254