JDK-8368993 : Parallel: JDK-8348278: Trim InitialRAMPercentage caused a performance regression in SPECjvm2008-SOR.small-ParGC
  • Type: Bug
  • Component: hotspot
  • Sub-Component: gc
  • Affected Version: 26
  • Priority: P2
  • Status: Closed
  • Resolution: Other
  • Submitted: 2025-10-01
  • Updated: 2025-12-16
  • Resolved: 2025-12-16
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JDK 26
26Resolved
Related Reports
Causes :  
JDK-8348278 - Trim InitialRAMPercentage to improve startup in default modes
Relates :  
JDK-8369346 - Remove default value of and deprecate the MaxRAM flag
Relates :  
JDK-8373023 - [REDO] Remove the default value of InitialRAMPercentage
Relates :  
JDK-8373712 - Regressions in 26+27 after JDK-8371986: Remove the default value of InitialRAMPercentage
Description
In SPECjvm2008-SOR small using Parallel GC we can observe a 36% regression on Linux aarch64. There seem to be a regression on about 1-2% for Linux x64 too but this is not statistically confirmed due to to a high variance.
Comments
I'm closing this after JDK-8373023 has been integrated, changing InitialRAMPercentage to 0. We will follow a similar (really the same regression but with new numbers) in JDK-8373712.
16-12-2025
The performance regression stems from a change to the initial heap size, which increases GC frequency. The higher GC frequency caused the observed regression. In all configurations, GC frequency remains low (below the permitted GC CPU percentage), so automatic heap resizing does not help -- this is an inherent footprint-versus-throughput trade-off. Two changes affect the initial heap size: JDK-8369346 and JDK-8369346. The machine has 1020G of RAM, and systems with large memory (>128G) are likely to experience the regression to varying degrees. Observed logs: - [0.009s][info][gc,init] Memory: 1020G Before JDK-8369346 (InitialRAMPercentage = 1.5): - [0.009s][info ][gc,init] Heap Initial Capacity: 2G After JDK-8369346 (InitialRAMPercentage = 0.2): - [0.009s][info][gc,init] Heap Initial Capacity: 288M After lifting MaxRam (post JDK-8369346): - [0.008s][info][gc,init] Heap Initial Capacity: 2112M After JDK-8369346, performance is roughly back to what was observed originally.
05-11-2025