JDK-8071277 : G1: Merge commits and uncommits of contiguous memory
  • Type: Enhancement
  • Component: hotspot
  • Sub-Component: gc
  • Affected Version: 9
  • Priority: P4
  • Status: Resolved
  • Resolution: Fixed
  • Submitted: 2015-01-21
  • Updated: 2025-10-07
  • Resolved: 2025-09-29
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JDK 26
26 b18Fixed
Related Reports
Duplicate :  
JDK-8348270 - G1 is slow at startup due to initial heap commits
Relates :  
JDK-8367993 - G1: Speed up ConcurrentMark initialization
Relates :  
JDK-8367992 - Card table clearing during commit significantly slows down VM startup
Relates :  
JDK-8359802 - JEP 523: Make G1 the Default Garbage Collector in All Environments
Description
Currently G1 does not merge commits (and uncommits) of contiguous memory if the commit page size is smaller than commit granularity.

This results in additional commit/uncommit calls that may be slow, particularly during startup (the commit)
Comments
Changeset: 08b677bb Branch: master Author: Thomas Schatzl <tschatzl@openjdk.org> Date: 2025-09-29 10:05:45 +0000 URL: https://git.openjdk.org/jdk/commit/08b677bba4b1e23feb55b104d86fe0eef543d59c
29-09-2025
A pull request was submitted for review. Branch: master URL: https://git.openjdk.org/jdk/pull/27381 Date: 2025-09-19 07:01:00 +0000
19-09-2025
As found during investigation of JDK-8348270, fixing this improves startup significantly: See https://bugs.openjdk.org/browse/JDK-8348270?focusedId=14818136&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#comment-14818136
18-09-2025
Patch contains merging the "commit" part
28-10-2015
Have a prototype for merging commits of contiguous memory. There is no measurable difference in doing that on larger heaps I tested (up to 100G)
10-04-2015