RFR: 8315781: Reduce the max value of GCDrainStackTargetSize

Wed Sep 6 12:26:55 UTC 2023

Simple adjustment to the max value of `GCDrainStackTargetSize`.

I picked 8K because the default queue capacity is ~16K and G1 use 2x of `GCDrainStackTargetSize` as some threshold.

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Commit messages:
 - g1-remove-default

Changes: https://git.openjdk.org/jdk/pull/15590/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15590&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8315781
  Stats: 9 lines in 4 files changed: 0 ins; 6 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/15590.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15590/head:pull/15590

PR: https://git.openjdk.org/jdk/pull/15590