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  1. JDK
  2. JDK-8224759

Investigate block splitting during heap root scan

    Details

    • Type: Enhancement
    • Status: Open
    • Priority: P4
    • Resolution: Unresolved
    • Affects Version/s: 13
    • Fix Version/s: tbd
    • Component/s: hotspot
    • Subcomponent:
      gc

      Description

      With JDK-8213108 consecutive dirty cards are scanned as a single block. This may result in pushing a lot of references to scan into the task queue (64kb chunk size, ie. 16k references max).

      During development of JDK-6672778 we found that having less references on the task queue is advantagous due to memory prefetching/caching reasons.

      Investigate the impact of splitting blocks on a smaller granularity than chunk size.

      BigRAMTester and SPECjbb2015 have a few GCs (at the start iirc) where the block/chunk size is very small, i.e. G1 can find many large blocks.

      Very short attempts on e.g. limiting block size to 4 cards (random number) showed no conclusive initial advantage or disadvantage in pause times.

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              • Assignee:
                Unassigned
                Reporter:
                tschatzl Thomas Schatzl
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                Dates

                • Created:
                  Updated: