RFR: 8304442: Allocate VirtualMemoryTracker into Arena

[Coleen Phillimore]

On Mon, 27 Mar 2023 11:24:38 GMT, Johan Sjölen <jsjolen at openjdk.org> wrote:

> Hi,
> 
> This is a suggestion to allocate the VirtualMemoryTracker memory inside of an Arena instead of on the heap. This reduces the number of NativeCallStacks allocated as VMT doesn't go through os::malloc for each linked list node. It also hopefully increases memory locality, as the nodes are in the best case allocated very close to each other.
> 
> This PR sees a performance improvement in os::commit_memory and reserve_memory of about 10-25%, at no cost to reporting.

These sorted regions are never deleted?

src/hotspot/share/services/virtualMemoryTracker.cpp line 120:

> 118:   VirtualMemoryRegion(base, size),
> 119:   _committed_regions(VirtualMemoryTracker::_backing_arena),
> 120:   _stack(NativeCallStack::empty_stack()), _flag(mtNone) { }

You shouldn't record anything with mtNone (not sure if this is what this does).

src/hotspot/share/services/virtualMemoryTracker.cpp line 127:

> 125:     _committed_regions(VirtualMemoryTracker::_backing_arena) {
> 126:     *this = rr;
> 127: }

(preexisting) since you have a copy constructor, should you have a deleted operator=?

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PR Review: https://git.openjdk.org/jdk/pull/13190#pullrequestreview-1359587493
PR Review Comment: https://git.openjdk.org/jdk/pull/13190#discussion_r1149602431
PR Review Comment: https://git.openjdk.org/jdk/pull/13190#discussion_r1149602739