RFR: 8280579: Shenandoah: Skip regions in the back of sorted array when choosing cset

[Yude Lin]

Can I have review on this small change that skips some unnecessary work in cset choosing?

When choosing regions to add to cset, we sort the regions from most garbage to least garbage. We then iterate the sorted array. We can break early from the loop if we find a region with (garbage <= garbage_threshold). Because we know the regions left won't have enough garbage and won't be added anyway.

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Commit messages:
 - 8280579: Shenandoah: Skip regions in the back of sorted array when choosing cset

Changes: https://git.openjdk.java.net/jdk/pull/7211/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7211&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8280579
  Stats: 4 lines in 1 file changed: 4 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7211.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7211/head:pull/7211

PR: https://git.openjdk.java.net/jdk/pull/7211