JDK-8272773 : Configurable card table card size
  • Type: Enhancement
  • Component: hotspot
  • Sub-Component: gc
  • Affected Version: 18
  • Priority: P4
  • Status: Resolved
  • Resolution: Fixed
  • Submitted: 2021-08-20
  • Updated: 2024-06-11
  • Resolved: 2021-11-20
The Version table provides details related to the release that this issue/RFE will be addressed.

Unresolved : Release in which this issue/RFE will be addressed.
Resolved: Release in which this issue/RFE has been resolved.
Fixed : Release in which this issue/RFE has been fixed. The release containing this fix may be available for download as an Early Access Release or a General Availability Release.

To download the current JDK release, click here.
JDK 18
18 b25Fixed
Related Reports
CSR :  
JDK-8275142 - Configurable card table card size
Relates :  
JDK-8334010 - G1: gc/g1/TestShrinkAuxiliaryDataRunner.java crashes with card table card sizes < ObjectAlignmentInBytes
Relates :  
JDK-8277854 - The upper bound of GCCardSizeInBytes should be limited to 512 for 32-bit platforms
Relates :  
JDK-8277373 - Make maximum card table size dependent on ObjectAlignmentInBytes
Relates :  
JDK-8277450 - Record number of references into collection set during gc
Relates :  
JDK-8328364 - Remove redundant fields in 'BOTConstants'
Relates :  
JDK-8277372 - Add getters for BOT and card table members
Relates :  
JDK-8309627 - Incorrect sorting of DirtyCardQueue buffers
Relates :  
JDK-8227174 - Lazily set card table of allocated regions to correct values in G1
Relates :  
JDK-8278901 - Parallel: Investigate impact of card size on card scanning work distribution
Relates :  
JDK-8275056 - Virtualize G1CardSet containers over heap region
Relates :  
JDK-8272774 - Allow heap region sizes larger than 32M with larger card table entry sizes
Sub Tasks
JDK-8277448 :  
Release Note: Configurable Card Table Card Size - Closed
Description
A card in the card table currently has a fixed constant size of 512 bytes for forever.

This can impact pause time significantly in g1 as it needs to clear the young gen card table in the pause.

If you increase the card table entry size, there may be significant savings on that time when the amount of regions the card table has to be cleared is large, as the attached spreadsheet shows for specjbb2015.

See what the impact on other applications and garbage collectors is when increasing the card table size, effectively making it startup time configurable.
Comments
Changeset: 1c215f33 Author: Vishal Chand <vishalchand2492@gmail.com> Committer: Thomas Schatzl <tschatzl@openjdk.org> Date: 2021-11-20 10:03:45 +0000 URL: https://git.openjdk.java.net/jdk/commit/1c215f33698ba2aef4fb230475a9bd33ed3005f9
20-11-2021
Suggested by V. Chand (https://mail.openjdk.java.net/pipermail/hotspot-gc-dev/2021-August/036197.html) Attached numbers are also from him.
23-08-2021