introduction-to-modern-gc

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ͬ͘͟Γ  Θ͔ͬͨؾʹͳΔ ϞμϯGC ೖ໳ JJUG CCC 2018 Spring @yokotaso

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

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͜Ε·ͰͷGC

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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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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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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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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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GCͱΞϓϦͷఀࢭ(STW) • ίϯύΫγϣϯGCͰఀࢭ  ੈ୅ܕGC͸Young GCͰఀࢭ  ੜଘͷΦϒδΣΫτͷ଴ආͰఀࢭ • ίϯύΫγϣϯ͠ͳ͍ͱϝϞϦ͕  ϑϥάϝϯτͯ͠͠·͏

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ͳͥ৽GCͳͷ͔

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৽͍͠GCͷඞཁੑ • ڊେώʔϓΛ࢖͏ΞϓϦέʔγϣϯͷ୆಄  ElasticsearchͳͲ • ίϯύΫγϣϯܕGCͷఀࢭΛ΍Ί͍ͨ  Young GC / G1GCͷίϯύΫγϣϯ • ώʔϓྖҬͷେ͖͞ͱGCͰͷఀࢭ͕࣌ؒൺྫ

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Shenandoah GC

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

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GCͷಛ௃ • ੈ୅ܕϝϞϦ؅ཧΛ͠ͳ͍ • ϦʔδϣϯܕͷϝϞϦ؅ཧ • ฒྻϚʔΩϯάɾฒྻίϯύΫγϣϯ • ΞϓϦέʔγϣϯͱฒྻͰಈ͔͠ͳ͕Β  ίϯύΫγϣϯGC͢Δ೉͠͞ͱ͸ʁ

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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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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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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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GC શମΛோΊͯΈΔ Region Region Region Region Root

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

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

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Final-Remark Root Region Region Region Region Concurrent-Markதʹൃੜͨ͠  ࢀরͷมߋ൓өɾΰϛΦϒδΣΫτͷ֬ఆ Stop the world

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Concurrent-Compaction Root Region Region Region Region ίϯύΫγϣϯ͢ΔϦʔδϣϯΛܾఆͯ͠  ΦϒδΣΫτΛୀආ͢Δ ୀආ͢ΔϦʔδϣϯ Concurrent

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Concurrent-Compaction Root Region Region Region Region ίϯύΫγϣϯ͢ΔϦʔδϣϯΛܾఆͯ͠  ΦϒδΣΫτΛୀආ͢Δ Concurrent

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

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

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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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ZGC

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ZGC • OracleͰ։ൃ͞ΕͨGC • ਺TBͷώʔϓͰ΋GCʹΑΔఀࢭ࣌ؒ͸  ୯ௐ૿Ճ͠ͳ͍ • 2018/05ɺόοΫϙʔτ͕ඞཁ • Linux 64bit ͷΈಈ࡞

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Shenandoah GCͱࣅ͍ͯΔ • ίϯηϓτ͸ Shenandoah GCͱಉ͡  ੈ୅؅ཧͳ͠ɾϦʔδϣϯܕͷϝϞϦ؅ཧ  ฒྻίϯύΫγϣϯ • Linux 64 bit OSͰ͔͠ར༻Ͱ͖ͳ͍

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ZGCͰಛ௃తͳ΋ͷ • ΧϥʔɾϙΠϯλ • Linux Ծ૝ϝϞϦͷ׆༻  64bitͷΞυϨεදݱΛϑϧ׆༻͢Δ • ϑΥϫʔσΟϯάɾςʔϒϧ

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

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

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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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ڊେϝϞϦͷਖ਼ମ͸Ծ૝Խ • ZGCͰ͸64bitΛ͢΂ͯ࢖͏ͷͰ128TBඞཁ • ͦΜͳڊେͳϝϞϦͳ͍ΜͰ͕͢…  ͦ͜ͰԾ૝ϝϞϦΛ࢖ͬͯղܾ͢Δ Linuxͷ͍͍ຊ͕࠷ۙͰͨΒ͍͠Ͱ͢Α

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GC શମΛோΊͯΈΔ Region Region Region Region Root

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

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

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Final-Remark Root Region Region Region Region Concurrent-Markதʹൃੜͨ͠ࢀরͷมߋ൓өͱ  ΰϛΦϒδΣΫτͷ֬ఆ Stop the world

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Concurrent-Compaction Root Region Region Region Region ίϯύΫγϣϯ͢ΔϦʔδϣϯΛܾఆ.  ΦϒδΣΫτΛ଴ආࡁΈͷ ͰϚʔΫͯ͠ɺୀආ͍ͯ͘͠ɻ ୀආ͢ΔϦʔδϣϯ Concurrent

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Concurrent-Compaction Root Region Region Region Region Concurrent ଴ආͨ͠ΦϒδΣΫτ͸  ϑΥϫʔσΟϯάςʔϒϧʹϙΠϯλΛه࿥ ϑΥϫʔσΟϯάɾςʔϒϧ

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ϑΥϫʔσΟϯάɾςʔϒϧ • Shenandoah GCͩͱΦϒδΣΫτ͝ͱʹ  ϔομʔΛ෇͚Δ෼ɺΦʔόʔϔου͕େ͖͍ • ΧϥʔϙΠϯλͷ͓͔͛ͰΦϒδΣΫτ͕  ݹ͍ɾ৽͍͠Λ൑அՄೳ • ϑΥϫʔσΟϯάɾςʔϒϧͰϝϞϦઅ໿

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ࢀরͷߋ৽͸ʁ

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

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

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

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Concurrent-Mark/Remap Root Region Region Region Region Concurrent ΦϒδΣΫτͷࢀরΛߋ৽΍଴ආ.  ϦʔδϣϯΛ׬શʹഇغ͢Δ ۭʹͳͬͨʂ ଴ආ

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Epsilon GC

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

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ͳͥͳΒ

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ͳʹ΋͠ͳ͍GC

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ʋ(ŋωŋ)/ţƄŠŖ

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Epsilon GC • JVM։ൃ༻ͷGC • ύϑΥʔϚϯεଌఆ࣌ʹGCͰͷੑೳྼԽΛ  ഉআ͢ΔͨΊ • ώʔϓ͕ຒ·Δͱ OutOfMemoryError • ຊ൪؀ڥͰ͸࢖Θͳ͍ͰͶ

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