introduction-to-modern-gc

Shenandoah GC・ZGC・Epsilon GCをざっくり理解したい！

JJUG CCC 2018 Spring での発表資料です

Transcript

1. ͬ͘͟Γ

   Θ͔ͬͨؾʹͳΔ
   ϞμϯGC ೖ໳
   JJUG CCC 2018 Spring @yokotaso
   

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2. Agenda
   • ͜Ε·ͰͷGCͱͳͥ৽GC͕ඞཁͳͷ͔
   • Shenandoah GC
   • ZGC
   • Epsilon GC
   

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3. ͜Ε·ͰͷGC
   

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4. GCͱΞϓϦఀࢭ(STW)
   Compaction GC
   Parallel GC
   young gc old gc
   GC = ΞϓϦέʔγϣϯεϨουఀࢭ
   ϝϞϦ͕ϑϥάϝϯτ͠ͳ͍
   CPUෛՙ͸খ͍͞
   Stop The world = ΞϓϦέʔγϣϯεϨουͷఀࢭ
   Mark Compaction GC
   Noop
   

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5. GCͱΞϓϦఀࢭ(STW)
   CMS GC Compaction GC
   young gc
   marking sweep GC
   old gc
   initial-mark final-remark
   young gc͸ΞϓϦέʔγϣϯεϨουఀࢭ
   major gc͸΄΅ฒྻ
   ϝϞϦͷϑϥάϝϯτ͕ܽ఺
   Stop The world = ΞϓϦέʔγϣϯεϨουͷఀࢭ
   Concurrent = ΞϓϦέʔγϣϯεϨουͱฒྻ
   

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6. GCͱΞϓϦఀࢭ(STW)
   G1GC Compaction GC
   young gc
   Marking
   old gc
   initial-mark final-remark
   young gc͸ΞϓϦέʔγϣϯεϨουఀࢭ
   major gc͸໨ඪఀࢭ࣌ؒΛݩʹGCΛߦ͏
   ϝϞϦ͕ϑϥάϝϯτ͠ͳ͍
   Stop The world = ΞϓϦέʔγϣϯεϨουͷఀࢭ
   Compaction GC
   Concurrent = ΞϓϦέʔγϣϯεϨουͱฒྻ
   

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7. GCͱΞϓϦఀࢭ(STW)
   Parallel GC
   CMS GC
   G1GC
   young gc
   Concurrent mark Concurrent sweep
   Mark
   Concurrent mark
   old gc
   Compaction GC
   Compaction GC
   Compaction GC Compaction GC
   Compaction GC
   Noop
   

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8. GCͱΞϓϦͷఀࢭ(STW)
   • ίϯύΫγϣϯGCͰఀࢭ

   ੈ୅ܕGC͸Young GCͰఀࢭ

   ੜଘͷΦϒδΣΫτͷ଴ආͰఀࢭ
   • ίϯύΫγϣϯ͠ͳ͍ͱϝϞϦ͕

   ϑϥάϝϯτͯ͠͠·͏
   

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9. ͳͥ৽GCͳͷ͔
   

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10. ৽͍͠GCͷඞཁੑ
    • ڊେώʔϓΛ࢖͏ΞϓϦέʔγϣϯͷ୆಄

    ElasticsearchͳͲ
    • ίϯύΫγϣϯܕGCͷఀࢭΛ΍Ί͍ͨ

    Young GC / G1GCͷίϯύΫγϣϯ
    • ώʔϓྖҬͷେ͖͞ͱGCͰͷఀࢭ͕࣌ؒൺྫ
    

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11. Shenandoah GC
    

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12. Shenandoah GC
    • Redhat͕ࣾ։ൃͨ͠GC
    • 100GBͱ2GBͷఀࢭ͕࣌ؒมΘΒͳ͍
    • 2018/05 όοΫϙʔτ͕ඞཁ
    

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13. GCͷಛ௃
    • ੈ୅ܕϝϞϦ؅ཧΛ͠ͳ͍
    • ϦʔδϣϯܕͷϝϞϦ؅ཧ
    • ฒྻϚʔΩϯάɾฒྻίϯύΫγϣϯ
    • ΞϓϦέʔγϣϯͱฒྻͰಈ͔͠ͳ͕Β

    ίϯύΫγϣϯGC͢Δ೉͠͞ͱ͸ʁ
    

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14. ฒྻίϯύΫγϣϯͷ໰୊఺
    Pointer
    x = 1
    y = 2
    z= 3
    Pointer
    x = 1
    y= 2
    z= 3
    GCεϨου͕Ҡಈத
    • GCεϨου͕ΦϒδΣΫτͷҠಈதʹ

    ϦϑΝϨϯεͷॻ͖׵͕͑ى͖ΔՄೳੑ
    Ͳ͕ͬͪຊ෺ʁ
    

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15. ΦϒδΣΫτͷϔομ͕ΩϞ
    Pointer
    Header
    ͜ΕΛղܾ͢ΔͨΊʹBrooks pointerΛಋೖ

    ϙΠϯλ͕ࣗ෼Ҏ֎ͷϔομΛࢦ͍ͯ͠Δ৔߹

    ͦͷઌͷΦϒδΣΫτΛࢀর͢Δ
    x = 1
    y = 2
    z = 3
    Pointer
    Header
    x = 1
    y= 2
    z= 3
    ຊ෺
    ผͷ৔ॴʹ଴ආ
    

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16. Brooks pointer
    Pointer
    Header
    x = 1
    y = 2
    z= 3
    Pointer
    Header
    x = 1
    y= 2
    z= 3
    ࢀরઌ͕ίϯύΫγϣϯ͞Εͨݹ͍ΦϒδΣΫτͳΒ
    ϔομʔΛͨͲͬͯɺ৽͍͠ΦϒδΣΫτΛࢀর͢Δ
    

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17. GC શମΛோΊͯΈΔ
    Region Region Region Region
    Root
    

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18. Initial-Mark
    Root
    Region Region Region Region
    Root͔ΒͨͲΕΔΦϒδΣΫτΛϚʔΫ͢Δ
    Stop the world
    

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19. Concurrent-Mark
    Root
    Region Region Region Region
    Initial-MarkͰϚʔΫͨ͠ΦϒδΣΫτΛͨͲͬͯϚʔΫ͢Δ
    Concurrent
    ௥Ճ͞Εͨࢀর
    ❌
    ࡟আ͞Εͨࢀর
    

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20. Final-Remark
    Root
    Region Region Region Region
    Concurrent-Markதʹൃੜͨ͠

    ࢀরͷมߋ൓өɾΰϛΦϒδΣΫτͷ֬ఆ
    Stop the world
    

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21. Concurrent-Compaction
    Root
    Region Region Region Region
    ίϯύΫγϣϯ͢ΔϦʔδϣϯΛܾఆͯ͠

    ΦϒδΣΫτΛୀආ͢Δ
    ୀආ͢ΔϦʔδϣϯ
    Concurrent
    

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22. Concurrent-Compaction
    Root
    Region Region Region Region
    ίϯύΫγϣϯ͢ΔϦʔδϣϯΛܾఆͯ͠

    ΦϒδΣΫτΛୀආ͢Δ
    Concurrent
    

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23. Concurrent-updateReference
    Root
    Region Region Region Region
    ࢀরઌͷϙΠϯλΛୀආઌʹߋ৽͢Δ
    Concurrent
    ৽͍͠ࢀর
    ଴ආઌʹϙΠϯλߋ৽
    

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24. Final-updateReference
    Root
    Region Region Region Region
    Concurrent-updateReferenceதʹൃੜͨ͠ߋ৽Λ൓ө͢Δ
    Stop the world
    ۭʹͳͬͨʂ
    

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25. GCશମΛͳ͕ΊͯΈΔ
    Initial Mark Final Remark
    Concurrent Mark
    Concurrent Compaction
    update Reference
    Concurrent update Reference
    final update Reference
    Application work Application work Application work
    ฒྻίϯύΫγϣϯͷ͓͔͛Ͱ

    ίϯύΫγϣϯ࣌ͷSTWΛͳͭͭ͘͠

    ϑϥάϝϯτΛ๷͙͜ͱ͕Ͱ͖ΔΑ͏ʹͳͬͨ
    Stop the world
    

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26. ZGC
    

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27. ZGC
    • OracleͰ։ൃ͞ΕͨGC
    • ਺TBͷώʔϓͰ΋GCʹΑΔఀࢭ࣌ؒ͸

    ୯ௐ૿Ճ͠ͳ͍
    • 2018/05ɺόοΫϙʔτ͕ඞཁ
    • Linux 64bit ͷΈಈ࡞
    

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28. Shenandoah GCͱࣅ͍ͯΔ
    • ίϯηϓτ͸ Shenandoah GCͱಉ͡

    ੈ୅؅ཧͳ͠ɾϦʔδϣϯܕͷϝϞϦ؅ཧ

    ฒྻίϯύΫγϣϯ
    • Linux 64 bit OSͰ͔͠ར༻Ͱ͖ͳ͍
    

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29. ZGCͰಛ௃తͳ΋ͷ
    • ΧϥʔɾϙΠϯλ
    • Linux Ծ૝ϝϞϦͷ׆༻

    64bitͷΞυϨεදݱΛϑϧ׆༻͢Δ
    • ϑΥϫʔσΟϯάɾςʔϒϧ
    

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30. ΧϥʔɾϙΠϯλ
    • ΦϒδΣΫτͷঢ়ଶΛΧϥʔͱͯ͠දݱ
    • ϚʔΫࡁ 0(marked0) ϚʔΫϑΣʔζʹ࢖͏
    • ϚʔΫࡁ 1(marked1) ޙͰৄ͘͠
    • ΦϒδΣΫτ଴ආࡁ (remapped)
    

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31. ΦϒδΣΫτͷΞυϨεදݱ
    42 bit
    ࠷େ4TBͷΞυϨεΛදݱͰ͖Δ
    4
    1
    17 bit
    ະ࢖༻
    ΧϥʔϙΠϯλΛදݱ
    1. 64bitͷΞυϨεۭؒશ෦࢖͏
    2. ώʔϓΞυϨε͸ԼҐ42bitΛར༻
    3. 4bitͰΧϥʔϙΠϯλͷ৭Λදݱ
    

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32. 64bitΞυϨεΛ࠷େݶར༻
    Heap(4TB)
    marked0
    marked1
    remapped
    0x0000040000000000
    0x0000000000000000
    0x0000080000000000
    0x00000C0000000000
    0x0000100000000000
    0x0000140000000000
    0x000010001234abcdef
    1. ΦϒδΣΫτ͸଴ආࡁΈ
    2. 001234abcdefʹ࣮ମ
    ZGCͰ͸64bitͷΞυϨεΛ࢖͏.ϝϞϦ͕128TBඞཁ
    

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33. ڊେϝϞϦͷਖ਼ମ͸Ծ૝Խ
    • ZGCͰ͸64bitΛ͢΂ͯ࢖͏ͷͰ128TBඞཁ
    • ͦΜͳڊେͳϝϞϦͳ͍ΜͰ͕͢…

    ͦ͜ͰԾ૝ϝϞϦΛ࢖ͬͯղܾ͢Δ
    Linuxͷ͍͍ຊ͕࠷ۙͰͨΒ͍͠Ͱ͢Α
    

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34. GC શମΛோΊͯΈΔ
    Region Region Region Region
    Root
    

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35. Initial-Mark
    Root
    Region Region Region Region
    Root͔ΒͨͲΕΔΦϒδΣΫτΛ ͰϚʔΫ͢Δ
    Stop the world
    

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36. Concurrent-Mark
    Root
    Region Region Region Region
    Initial-MarkͰϚʔΫͨ͠ΦϒδΣΫτΛͨͲͬͯϚʔΫ͢Δ
    Concurrent
    ௥Ճ͞Εͨࢀর
    ❌
    ࡟আ͞Εͨࢀর
    

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37. Final-Remark
    Root
    Region Region Region Region
    Concurrent-Markதʹൃੜͨ͠ࢀরͷมߋ൓өͱ

    ΰϛΦϒδΣΫτͷ֬ఆ
    Stop the world
    

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38. Concurrent-Compaction
    Root
    Region Region Region Region
    ίϯύΫγϣϯ͢ΔϦʔδϣϯΛܾఆ.

    ΦϒδΣΫτΛ଴ආࡁΈͷ ͰϚʔΫͯ͠ɺୀආ͍ͯ͘͠ɻ
    ୀආ͢ΔϦʔδϣϯ
    Concurrent
    

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39. Concurrent-Compaction
    Root
    Region Region Region Region
    Concurrent
    ଴ආͨ͠ΦϒδΣΫτ͸

    ϑΥϫʔσΟϯάςʔϒϧʹϙΠϯλΛه࿥
    ϑΥϫʔσΟϯάɾςʔϒϧ
    

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40. ϑΥϫʔσΟϯάɾςʔϒϧ
    • Shenandoah GCͩͱΦϒδΣΫτ͝ͱʹ

    ϔομʔΛ෇͚Δ෼ɺΦʔόʔϔου͕େ͖͍
    • ΧϥʔϙΠϯλͷ͓͔͛ͰΦϒδΣΫτ͕

    ݹ͍ɾ৽͍͠Λ൑அՄೳ
    • ϑΥϫʔσΟϯάɾςʔϒϧͰϝϞϦઅ໿
    

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41. ࢀরͷߋ৽͸ʁ
    

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42. GCશମΛͳ͕ΊͯΈΔ
    Initial Mark Final Remark
    Concurrent Mark
    Concurrent Compaction
    Application work Application work
    

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43. GCશମΛͳ͕ΊͯΈΔ
    ark Final Remark
    oncurrent Mark
    Concurrent Compaction
    pplication work Application work
    Initial Mark Final Remark
    Concurrent Mark/Remap
    Concurrent Compaction
    Application work Application work
    GC1प໨
    GC2प໨
    

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44. ࢀরͷߋ৽͸࣍ͷGCαΠΫϧͰ
    • ࢀরͷߋ৽͸࣍ͷConcurrent-Markதʹ΍Δ
    • ਖ਼໊ࣜশ͸Concurrent-Mark/Remap
    • ࢀরΛͨͲΔճ਺Λઅ໿
    • ϚʔΩϯά͞ΕͨΦϒδΣΫτ͸

    ͍ͭͷGCαΠΫϧͰϚʔΩϯά͞Εͨʁ
    

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45. Concurrent-Mark/Remap
    Root
    Region Region Region Region
    Concurrent
    ৽͘͠௥Ճ͞Εͨࢀর͸ΧϥʔϙΠϯλͷ
    ϑϥά͕ҧ͏ͷͰɺ ͰϚʔΫ͠ͳ͓͠
    ϑΥϫʔσΟϯάɾςʔϒϧ
    ࢀর͕௥Ճ͞ΕͨͷͰ

    ϚʔΫ͠௚͠
    

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46. Concurrent-Mark/Remap
    Root
    Region Region Region Region
    Concurrent
    ΦϒδΣΫτͷࢀরΛߋ৽΍଴ආ.

    ϦʔδϣϯΛ׬શʹഇغ͢Δ
    ۭʹͳͬͨʂ
    ଴ආ
    

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47. Epsilon GC
    

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48. Epsilon GC
    • ΞϓϦέʔγϣϯεϨου͸ఀࢭ͠ͳ͍
    • CPUͷෛՙ͸΄ͱΜͲͳ͠
    • GCͷ࣌ؒ͸ݶΓͳ͘0ʹ͍ۙ
    

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49. ͳͥͳΒ
    

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50. ͳʹ΋͠ͳ͍GC
    

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51. ʋ(ŋωŋ)/ţƄŠŖ
    

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52. Epsilon GC
    • JVM։ൃ༻ͷGC
    • ύϑΥʔϚϯεଌఆ࣌ʹGCͰͷੑೳྼԽΛ

    ഉআ͢ΔͨΊ
    • ώʔϓ͕ຒ·Δͱ OutOfMemoryError
    • ຊ൪؀ڥͰ͸࢖Θͳ͍ͰͶ
    

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53. ·ͱΊ
    • ڊେώʔϓɾଟίΞલఏΞϓϦέʔγϣϯ༻GC

    ఀࢭ͕࣌ؒ໰୊ͳΒݕ౼ͷՁ஋͋Γ
    • Linux 64 bit OSͳΒ ZGC
    • ͦΕҎ֎ͳΒ Shenandoah GC
    • Epsilon GC͸Կ΋͠ͳ͍GC
    

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