Javascript:SpiderMonkey:ProjectGenerationGarbageCollection

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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, evilpie and Ms2ger
Consulted: bhackett billm
Informed: Product Marketing

Tracking Bug: [meta] Implement generational garbage collection - bug 619558

Milestones

Endgame schedule

Milestone Estimated Date Actual Date Nightly Version
All Hazards found by static analysis have been fixed 2013-08-30 26
Static analysis is unhidden on TBPL 2013-09-02 26
All Exact Rooting crashes found by fuzzers have been fixed 2013-09-__ 26
Nightly 26 is uplifted to Aurora 2013-09-16 2013-09-16 27
Exact Rooting is enabled 2013-09-17 27
All GGC crashes found by fuzzers have been fixed 2013-09-__ 27
AWFY with GGC >= AWFY without GGC 2013-09-__ 27
GGC is enabled for desktop and Android 2013-09-30 27
GGC is enabled for B2G 2013-10-__ 27
Nightly 27 is uplifted to Aurora 2013-10-28 2013-10-28 28

Original schedule

Milestone Task Deliverable Assigned Estimated Weeks Expected Date Actual Date
1 Rooting analysis in the shell (x64) green on mozilla-inbound sfink, jonco, evilpie, Ms2ger 2 3/7/2013 3/2/2013
2 Rooting analysis in the shell (arm) green on mozilla-inbound sfink 2 pending
3 Exactly rooted shell (x64) green on mozilla-inbound sfink, jonco, evilpie, Ms2ger 2 3/14/2013 done?
4 Exactly rooted shell (arm) green on mozilla-inbound sfink 2 pending
4.1 Exactly rooted js/src green on mozilla-inbound jonco 3 5/9/2013 in progress
5 GGC no-jit shell only build on TBPL (x64) green on mozilla-inbound terrence 6 2/21/2013 4/7/2013
6 GGC no-jit shell only build on TBPL (arm) green on mozilla-inbound sfink, terrence 2 pending
7 JIT support (x64) (Bug 706885) TBPL build using JITs and Ion+Baseline+GGC displayed on AWFY bhacket 8 3/15/2013 4/7/2013
8 JIT support (arm) TBPL build using JITs and Ion+Baseline+GGC displayed on AWFY bhacket 2 pending
9 Optimized GGC in shell (x64 + arm) Ion+GGC faster than Ion-GGC on AWFY bhacket 12 6/1/2013 not started
10 Static rooting analysis - browser available via mrgiggles and URL sfink, bhacket 12 6/1/2013 done
10.1 Static analysis on TBPL - browser visible on tbpl sfink not started
10.2 Static rooting analysis - b2g available via mrgiggles and URL sfink pending
10.3 Static analysis on TBPL - b2g visible on tbpl sfink not started
11 Exactly rooted browser (x64 + arm) green on mozilla-inbound sfink, jonco, evilpie, Ms2ger, terrence 16 7/1/2013 in progress
12 GGC in the browser (x64 + arm) green on AWFY terrence 16 10/1/2013 not started

Steps

Exact Rooting done in JS Shell bug 753203

12 weeks started

JIT Integration with post barriers - 4 weeks, parallelized

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| - done.
  • Re-implement HashTable rekeying
    • We undid this code because it was a perf regression and was still a bit buggy. (terrence) - 3 weeks
    • at least part of this is bug 726687

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.

Performance Tuning - 4 weeks (This should probably start asap)

  • Implement a Nursery bug 706885 - 1 week
  • 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 bug 759585 - 6 weeks - done
  • Refactor code to avoid rooting on hot paths and keep rooter overhead acceptable bug 831886 (bhackett) - done

Make the Post Barrier Verifier Green in the browser bug 764882

  • 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.
  • 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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