RFR: 8268127: Shenandoah: Heap size may be too small for region to align to large page size [v2]

[Zhengyu Gu]

> TestLargePages.java failed on Linux AArch64, where large page size is 500M, and the test is configured to run with much smaller heap, e.g. 131M.
> 
> This is *not* AArch64 specific, just none of our regular test machines has large page setup.
> 
> I purpose two invariants:
> 1) Heap size always aligns up to page size that is requested.
> 2) Region size always aligns up to page size that is requested if heap is large enough to accommodate them. Otherwise, it aligns up to regular page size.
> 
> This partially reverts JDK-8266802.
> 
> Obviously, this is a corner case and is unlikely seen in real word. The alternative is to disable UseLargePages if heap size is too small, e.g. align_up(heap_size, page_size) < MIN_NUM_REGIONS.
> 
> Test:
>   hotspot_gc_shenandoah

Zhengyu Gu has updated the pull request incrementally with one additional commit since the last revision:

  Fix compilation error

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/4320/files
  - new: https://git.openjdk.java.net/jdk/pull/4320/files/892d07be..1e0e8320

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=4320&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=4320&range=00-01

  Stats: 2 lines in 2 files changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4320.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4320/head:pull/4320

PR: https://git.openjdk.java.net/jdk/pull/4320