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  1. JDK
  2. JDK-8233862

Investigate performance benefit of relocating CDS archive to under 32G



      According to Jiangli: "When enabling CDS we [google] noticed a small runtime overhead in JDK 11 recently with a benchmark. After I backported JDK-8213713 to 11, it seemed to reduce the runtime overhead that the benchmark was experiencing."

      (Note: without JDK-8213713, using CDS will cause a 1GB gap in the compressed klass space, which starts at 0x800000000 on Linux/x64)

      With JDK-8231610, the CDS archive will be automatically relocated if it cannot be mapped at 0x800000000. As a result, the compressed klass space might be mapped to much higher than 32GB. Jiangli is worried that this might cause VM slow down (as she experienced with the backport of JDK-8213713), and suggested that it may be beneficial to try to relocated the CDS archive to under 32GB.

      I ran a few benchmarks (Octane-DeltaBlue,
      Octane-NavierStokes, SPECjbb2005-Tuned, JFR-SPECjbb2005-Tuned, SPECjvm2008-Serial-G1, Tools-Javac-Hello) and did not see regression when the CDS archive is relocated.

      This RFE is a reminder for further evaluation to see if this is indeed an issue that needs to be addressed.




            • Assignee:
              iklam Ioi Lam
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