RFR: 8254739: G1: Optimize evacuation failure for regions with few failed objects [v18]

Hamlin Li mli at openjdk.java.net
Wed Nov 3 01:09:34 UTC 2021

> This is a try to optimize evcuation failure for regions.
> I record every evacuation failure object per region (by G1EvacuationFailureObjsInHR), and then iterate (which indeed includes compact/sort/iteration) these objects directly in RemoveSelfForwardPtrHRClosure.
> I have tested it with following parameters, 
> -   -XX:+ParallelGCThreads=1/32/64
> -   -XX:G1EvacuationFailureALotInterval=1
> -   -XX:G1EvacuationFailureALotCount=2/10/100/1000/10000/100000
> It saves "Remove Self Forwards" time all the time ,and in most condition it saves "Evacuate Collection Set" time. 
> It brings some performance degradation when -XX:G1EvacuationFailureALotCount is low, such as *2*. To improve this a little, we can record the number evacuation failure object per region, and not record these objects when the number hit some limit. But I'm not sure if it's necessary to do so, as I think such condition is so extreme to be met in real environment, although I'm not quite sure.

Hamlin Li has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 19 commits:

 - Merge branch 'openjdk:master' into speedup-iterate-evac-failure-objs-in-one-region
 - Refine code based on Thomas' suggestion
 - Merge branch 'openjdk:master' into speedup-iterate-evac-failure-objs-in-one-region
 - Fix compilation error
 - Fix compilation error
 - Refactor as Thomas suggested
 - Rename from g1EvacuationFailureObjsInHR to g1EvacFailureObjsInHR
 - Add asserts, comments
 - Use refactored G1SegmentedArray rather than home-made Array+Node
 - Fix wrong merge
 - ... and 9 more: https://git.openjdk.java.net/jdk/compare/bb92fb02...d33f87b4


Changes: https://git.openjdk.java.net/jdk/pull/5181/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5181&range=17
  Stats: 349 lines in 12 files changed: 311 ins; 5 del; 33 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5181.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5181/head:pull/5181

PR: https://git.openjdk.java.net/jdk/pull/5181

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