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  1. JDK
  2. JDK-8040162

Avoid reallocating PLABs between GC phases in G1

    Details

    • Type: Enhancement
    • Status: Resolved
    • Priority: P4
    • Resolution: Fixed
    • Affects Version/s: 9
    • Fix Version/s: 9
    • Component/s: hotspot
    • Subcomponent:
      gc
    • Resolved In Build:
      b81

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        Description

        Currently G1 uses separate allocation buffers for the different gc phases (evacuation, soft reference processing): however, PLAB size is determined by overall allocation behavior. It is very expensive in terms of memory usage to size the buffers the same in phases that have a wildly different allocation behavior: evacuation typically allocates a lot, while other phases (soft reference processing) does not.

        This often wastes a lot of memory at the end of the phases that do not allocate a lot. Particularly in the soft-reference processing phase, very often only a few objects are kept alive, although G1 sizes the buffer to the same size as for the actual evacuation phase which has a lot more survivors.

        Fix this.

        One suggestion is to use per-thread single instances of G1ParGCAllocBuffers during the whole GC phase.

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                • Assignee:
                  tschatzl Thomas Schatzl
                  Reporter:
                  tschatzl Thomas Schatzl
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                  • Created:
                    Updated:
                    Resolved: