RFR: JDK-8266802: Shenandoah: Round up region size to page size unconditionally [v3]

[Aleksey Shipilev]

> Since JDK-8265239, runtime/os/TestTracePageSizes.java fails with Shenandoah like this:
> 
> 
> # Internal Error (/home/buildbot/worker/test-jdkX-linux/build/src/hotspot/share/gc/shenandoah/shenandoahHeap.cpp:156), pid=55712, tid=55720
> # assert(_num_regions == (max_byte_size / reg_size_bytes)) failed: Must match
> 
> 
> This is because Shenandoah region sizes are rounded up to page size only when `ShenandoahUncommit` is true. In the failing test configuration, `ShenandoahUncommit` is false, because Xmx == Xms.
> 
> Additional testing:
>  - [x] New regression test, now passes
>  - [x] `tier1` with Shenandoah

Aleksey Shipilev has updated the pull request incrementally with one additional commit since the last revision:

  UseTransparentHugePages is only available on Linux

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/3945/files
  - new: https://git.openjdk.java.net/jdk/pull/3945/files/96a4778b..dd3ba65d

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=3945&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=3945&range=01-02

  Stats: 12 lines in 1 file changed: 11 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3945.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3945/head:pull/3945

PR: https://git.openjdk.java.net/jdk/pull/3945