RFR: JDK-8260200 G1: Remove unnecessary update in FreeRegionList::remove_starting_at [v4]

[Hamlin Li]

> optimize FreeRegionList::remove_starting_at by removing unnecessary reading and setting
> 
> FreeRegionList::remove_starting_at(...) traverses from a node and removes subsequent N nodes from free list. But when traverses the free list, it removes nodes one by one by setting the prev and next pointers of prev and next node. it's not necessary do these settings for every node, as we can remove target nodes at once and just set prev and next pointers for just 2 nodes.

Hamlin Li has updated the pull request incrementally with one additional commit since the last revision:

  JDK-8260200: G1: Remove unnecessary update in FreeRegionList::remove_starting_at

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/2181/files
  - new: https://git.openjdk.java.net/jdk/pull/2181/files/27c85ec5..30ec12f1

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=2181&range=03
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=2181&range=02-03

  Stats: 37 lines in 2 files changed: 19 ins; 16 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2181.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2181/head:pull/2181

PR: https://git.openjdk.java.net/jdk/pull/2181