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Javascript:SpiderMonkey:ProjectGenerationGarbageCollection

Revision as of 20:57, 5 February 2013 by Sfink (talk | contribs) (→‎Steps)

Wiki conversion of original Google Document: https://docs.google.com/a/jamsni.com/document/d/1-GZ8F0ZabvdpCnRQaecId0yuu4QFYr5pAvnRC_KFchc/edit


Objective

Implement Generational Garbage collection in Spider Monkey. <Some goal based off V8 performance delta % on Earley Boyer benchmark>

  • Accountable: Naveed
  • Responsible: Terrence, Steve, Jon, Nicholas, and evilpie Ms2ger
  • Consulted: bhackett billm
  • Informed: Product Marketing

Generational GC - bug 619558

Steps

  1. Exact Rooting done in JS Shell bug 753203 - 12 weeks started
    • Rooting Analysis on TinderBox (sfink) - done
      • Still need to unhide it for inbound - get it green, keep it green
    • Get the root analysis build green - two weeks?
    • Rooting analysis fuzz bugs bug 773746
      • Rely on static analysis to make this not be a whack-a-mole game
    • Remove E4X - done
    • Do something about JSD
    • Add exact roots to stack structures - 2 weeks
    • AddRoot/RemoveRoot for Heap structures - 4 weeks
    • Static code analysis bug 831409
  2. JIT Integration with post barriers - 4 weeks, parallelized
  3. Generational Garbage Collection in the Shell
    • Implement prototype algorithm (terrence) - 1 week
    • This is a potential milestone: we would need to build it and test it on TBPL similar to how |r| works now -- |GGCJS|.
    • Re-implement HashTable rekeying
      • We undid this code because it was a perf regression and was still a bit buggy. (terrence) - 3 weeks
    • Implement a Nursery bug 706885 - 1 week
  4. Exactly Root the Browser bug 831379 - 10 weeks
    • This is a potential milestone: we would turn on exact rooting for release FF at this point. We would not get a performance boost from this (necessarily), but it would lock in our work to this point.
  5. Performance Tuning - 4 weeks (This should probably start asap)
    • Test against V8 Earley-Boyer benchmark.
    • Also v8 deltablue, raytrace
    • We may need to Implement Bill’s Pools/Zones idea to get the nursery to the requisite perf - 6 weeks
    • Refactor code to avoid rooting on hot paths and keep rooter overhead acceptable - ??? weeks (start early) (bhackett)
  6. Make the Post Barrier Verifier Green in the browser bug 764882
  7. Investigate how long it will take to do generational barriers - 1 week
    • We may need to rewrite the maps in xpconnect and the browser in terms of HashTable: this could be a bunch of work.
  8. Make JS_IsAboutToBeFinalized indirect bug 765432 - 10 weeks

Other

  • Should we establish a new benchmark specifically for GGC. (sfink votes yes)
    • What would it measure? there are multiple goals, e.g. throughput/MMU/pause time
    • Should we make it a public benchmark?
    • What workloads should we consider?
    • compartmental GC very important to us, not necessarily applicable to other implementations
    • allocation rate (broken down into live vs garbage), steady behavior vs swapping between allocation + computation modes, etc.
  • How can we keep our advantage on Splay benchmark
    • possible to do with TI --- look at types of objects promoted from nursery to major heap, eventually start allocating them directly in the major heap
  • Compacting GC - Revisit in Febuary/March - 1 Month
    • Delayed until exact rooting is fully done. We can add this in if we have time in the schedule that we cannot parallelize.

Risks

  • Team is responsible for many top crashers
  • External rooting API has not been designed
  • GGC algorithm has not been decided on - it may not be faster
  • JSD1 exact rooting is lurking
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