RFR: 8256155: 2M large pages for code when LargePageSizeInBytes is set to 1G for heap

[Marcus G K Williams]

Use 2m pages for executable large
pages and in large page requests less
than 1g on linux.

- Add os::exec_large_page_size() that
returns 2m as size
- Add os::select_large_page_size() to return
correct large page size for size_t bytes
- Add 2m size to _page_sizes array
- Update reserve_memory_special methods
to set/use large_page_size based on exec
size
- Update large page not reserved warnings
to include large_page_size attempted
- Update TestLargePageUseForAuxMemory.java
to expect 2m large pages in some instances

Signed-off-by: Marcus G K Williams <marcus.williams at intel.com>

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Commit messages:
 - Default to 2M LargePages for code

Changes: https://git.openjdk.java.net/jdk/pull/1153/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1153&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8256155
  Stats: 99 lines in 3 files changed: 69 ins; 0 del; 30 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1153.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1153/head:pull/1153

PR: https://git.openjdk.java.net/jdk/pull/1153