> This is a test bug.  The gets the first region, gets top() for the that 
> region, and then uses that top() address to get the region that top() is in. 
> It expects it to be the same region. However, when the region is full, top() 
> is actually the next address beyond the end of the region, so marks the start 
> of the next region. The fix is to simply subtract 1 from top() when it equals 
> end(). Note top() is where the next allocation comes from in the region and 
> end() is the end of region space.
> 
> I improved the test by adding printing of the G1 heap, including all regions. 
> I also improved the test by making it test every region, not just the first 
> one. During local testing the first region was always free, so did not make 
> for a very good test, and would not reproduce the issue. When I started 
> testing every region, it failed every time. All you need is one full region 
> for failures.
> 
> I ran the test 100 times on all supported platforms.
> 
> ---------
> - [x] I confirm that I make this contribution in accordance with the [OpenJDK 
> Interim AI Policy](https://openjdk.org/legal/ai).

Chris Plummer has updated the pull request incrementally with one additional 
commit since the last revision:

  get rid of unneeded module

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/31469/files
  - new: https://git.openjdk.org/jdk/pull/31469/files/3d9adb41..70e9387e

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=31469&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=31469&range=00-01

  Stats: 2 lines in 1 file changed: 0 ins; 2 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/31469.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/31469/head:pull/31469

PR: https://git.openjdk.org/jdk/pull/31469

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