JDK-8256303 : revisit ObjectMonitor padding between fields
  • Type: Enhancement
  • Component: hotspot
  • Sub-Component: runtime
  • Affected Version: 16
  • Priority: P4
  • Status: Open
  • Resolution: Unresolved
  • OS: generic
  • CPU: generic
  • Submitted: 2020-11-12
  • Updated: 2024-01-10
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JDK 23
23Unresolved
Related Reports
Relates :  
JDK-8253064 - monitor list simplifications and getting rid of TSM
Relates :  
JDK-8257975 - Regression ~ 2.5% in SwingMark.Table after JDK-8253064
Description
[~rehn] mentioned this RFE during the JDK-8253064 review: 

 src/hotspot/share/runtime/objectMonitor.hpp
  DEFINE_PAD_MINUS_SIZE(0, OM_CACHE_LINE_SIZE, sizeof(volatile markWord) +
                        sizeof(WeakHandle) + sizeof(AllocationState));
                        sizeof(WeakHandle));
  // Used by async deflation as a marker in the _owner field:


I have test with and without padding, I saw no difference.
Comments
I won't have time to investigate this issue for JDK19.
04-05-2022
The dust has not settled on the performance bugs that were logged against JDK-8253064 so making more changes that might make performance worse would not be a good idea. Changing to 'tbd'.
20-05-2021
[~rehn] - Feel free to edit the bug to make things more clear since all I did was copy stuff from the PR.
12-11-2020