RFR: 8304442: Allocate VirtualMemoryTracker into Arena

[Johan Sjölen]

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.

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Commit messages:
 - Replace comment style
 - Allocate VirtualMemoryTracker in Arena

Changes: https://git.openjdk.org/jdk/pull/13190/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13190&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8304442
  Stats: 51 lines in 2 files changed: 29 ins; 12 del; 10 mod
  Patch: https://git.openjdk.org/jdk/pull/13190.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13190/head:pull/13190

PR: https://git.openjdk.org/jdk/pull/13190