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  1. JDK
  2. JDK-8234336

Improve G1 per-region predictions by discounting waste


    • Type: Enhancement
    • Status: Open
    • Priority: P4
    • Resolution: Unresolved
    • Affects Version/s: 14
    • Fix Version/s: tbd
    • Component/s: hotspot
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      Currently (and particularly after JDK-8231579) assumes that eden regions are completely filled in its calculation of survival ratios.

      Investigate the impact of this ratio calculation on the prediction by not assuming that eden regions are completely filled, but have various amounts of waste in them.

      E.g. end-of-region fill-up waste, and potentially waste at the end of regions.

      This results in the survival ratio to be way too low, particular for the last region which we sometimes (particularly in NUMA) end up filling early, thrashing the prediction for that region.

      An example: Assume that the last region is only filled half, and for some reason the actual survival rate is 50%. So instead of updating the predictors with 50% survival ratio, the current value used for updating is 25%.

      Another example would be waste at the end of TLAB, where the default sizing goal is 10% waste. Assuming again an actual survival rate of 50%, the value the current prediction is 45% (50% of 100-10%).


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              • Assignee:
                tschatzl Thomas Schatzl
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