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[UE4]GarbageCollectの対象周りを調べてみた

Unreal Engine 4 (UE4) Advent Calendar 2018の12月10日の記事です。
1. [UE4]InstancedStaticMeshのInstanceIDを何とかしてマテリアルで取得する
2. [UE4]GarbageCollectの対象周りを調べてみた

UE4.21.1で検証

→UE4.25でUPropery系がUObjectから外された影響でこの記事の話は無くなりそうです

ログの表示

コンソールコマンド

log LogGarbage Verbose

LogGarbage: Collecting garbage   (GCheckForIllegalMarkPendingKill = 1)
LogGarbage: Verbose: 25.012325 ms for Mark Phase (44975 Objects To Serialize
LogGarbage: Verbose: 4.298625 ms for Reachability Analysis
LogGarbage: 29.482862 ms for GC
LogGarbage: 0.056010 ms for Gather Unreachable Objects (5 objects collected including 0 cluster objects from 0 clusters)
LogGarbage: 0.023569 ms for unhashing unreachable objects. Items 5 (5/5)
LogGarbage: GC purged 5 objects (47621 -> 47616)

obj list

                                                                                                Class    Count      NumKB      MaxKB   ResExcKB  ResExcDedSysKB  ResExcShrSysKB  ResExcDedVidKB  ResExcShrVidKB     ResExcUnkKB
                                                                                                Class     1720    1115.12    1277.75       0.00            0.00            0.00            0.00            0.00            0.00
                                                                                             Function     4560     932.32    1046.28       0.00            0.00            0.00            0.00            0.00            0.00
                                                                                       StructProperty     5735     716.88     716.88       0.00            0.00            0.00            0.00            0.00            0.00
                                                                                         BoolProperty     4384     548.00     548.00       0.00            0.00            0.00            0.00            0.00            0.00
                                                                                        FloatProperty     3674     430.55     430.55       0.00            0.00            0.00            0.00            0.00            0.00
                                                                                       ObjectProperty     2819     352.38     352.38       0.00            0.00            0.00            0.00            0.00            0.00
                                                                                         ScriptStruct     1277     241.05     296.38       0.00            0.00            0.00            0.00            0.00            0.00
33160 Objects (Total: 6.478M / Max: 6.955M / Res: 34.187M | ResDedSys: 1.233M / ResShrSys: 0.000M / ResDedVid: 32.936M / ResShrVid: 0.000M / ResUnknown: 0.018M)

UObjectの数を表示できる。=GC対象
ゲームプレイしていると、やたらGC削除対象が多い……
とか思った時に、然るべきタイミングでの差分を見て何が増えたのか調べたり。

Blueprint Stats Plugin

2018-12-08_21h15_46.png

DumpBlueprintStats

が使えるようになる
(ただパッケージ版で使えなかったり、BP指定して個別のstats取れないの使いにくくない……?まだExperimentalっぽい?
 BP指定してその1つのBPでのstats取れるように拡張すると便利そう)

Cmd: DumpBlueprintStats
LogBlueprintStats: Blueprint stats for 19 blueprints in TestGC
LogBlueprintStats: Total,DOBP,NumNodes,ImpureWI,ImpureWO,ImpureWIO,ImpureTotal,PureTotal,UserFnCount,UserPureCount,UserMacroCount
LogBlueprintStats: 19,6,1088,81,14,10,84,416,19,1,30

どれが幾つ有るか

LogBlueprintStats: NodeClass,NumInstances
LogBlueprintStats: K2Node_CallFunction,310
LogBlueprintStats: K2Node_CommutativeAssociativeBinaryOperator,154
LogBlueprintStats: K2Node_VariableGet,112
LogBlueprintStats: EdGraphNode_Comment,63

各ノードのインスタンスが幾つ有るか

LogBlueprintStats: FunctionPath,ClassName,FunctionName,NumInstances
LogBlueprintStats: /Script/Engine.KismetStringLibrary:Concat_StrStr,KismetStringLibrary,Concat_StrStr,127
LogBlueprintStats: /Script/Engine.KismetStringLibrary:BuildString_Int,KismetStringLibrary,BuildString_Int,25
LogBlueprintStats: /Script/Engine.KismetTextLibrary:Conv_FloatToText,KismetTextLibrary,Conv_FloatToText,19
LogBlueprintStats: /Script/Engine.KismetTextLibrary:Conv_TextToString,KismetTextLibrary,Conv_TextToString,19

各関数のインスタンスが幾つ有るか

参考

検証してみた

  1. 空っぽのレベルを用意 2018-12-08_23h11_21.png
  2. レベルBPで、ボタンを押すとSpawn/Destroyするノード組む 2018-12-08_23h12_36.png
  3. SpawnするBPはActor継承した空っぽのBP
  4. Developmentパッケージングして確認
  • gc.MaxObjectsNotConsideredByGC
LogUObjectArray: 34975 objects as part of root set at end of initial load.
LogUObjectArray: 2 objects are not in the root set, but can never be destroyed because they are in the DisregardForGC set.
LogUObjectAllocator: 5223472 out of 0 bytes used by permanent object pool.
LogUObjectArray: CloseDisregardForGC: 34975/34975 objects in disregard for GC pool

数値取ったけど、以後のパターンどれでも数値は変わらず。

  • GCログ
// Spawn前
LogGarbage: Collecting garbage   (GCheckForIllegalMarkPendingKill = 1)
LogGarbage: Verbose: 0.009153 ms for Mark Phase (11 Objects To Serialize
LogGarbage: 0.004157 ms for Gather Unreachable Objects (0 objects collected including 0 cluster objects from 0 clusters)
LogGarbage: GC purged 0 objects (169 -> 169)
// Spawn後
LogBlueprintUserMessages: [NewMap_C_2] Spawn
LogGarbage: Collecting garbage   (GCheckForIllegalMarkPendingKill = 1)
LogGarbage: Verbose: 0.009984 ms for Mark Phase (11 Objects To Serialize
LogGarbage: 0.004161 ms for Gather Unreachable Objects (0 objects collected including 0 cluster objects from 0 clusters)
LogGarbage: GC purged 0 objects (171 -> 171)
// Destroy後
LogBlueprintUserMessages: [NewMap_C_2] Destroy
LogGarbage: Collecting garbage   (GCheckForIllegalMarkPendingKill = 1)
LogGarbage: Verbose: 0.006378 ms for Mark Phase (11 Objects To Serialize
LogGarbage: 0.004437 ms for Gather Unreachable Objects (2 objects collected including 0 cluster objects from 0 clusters)
LogGarbage: 0.011645 ms for incrementally unhashing unreachable objects. Items 2 (2/2)
LogGarbage: GC purged 2 objects (171 -> 169)

Spawn前のGC対象のオブジェクトは169。
Spawnした後のGC対象のオブジェクトは171。空BPでオブジェクトが2つ増えた。
DestroyでGCに2個持っていかれた
ちなみに、2回Spawnしても173になるだけ。

  • obj listの差分
// Spawn前
SceneComponent        6
// Spawn中
SceneComponent        7
BP_Test_C             1

GCに持っていかれたのはこの2つ

SpawnするBPに変数増やしてみた

2018-12-09_00h15_04.png

  • GCログ
// Spawn前
LogGarbage: Collecting garbage   (GCheckForIllegalMarkPendingKill = 1)
LogGarbage: Verbose: 0.006378 ms for Mark Phase (11 Objects To Serialize
LogGarbage: 0.004157 ms for Gather Unreachable Objects (0 objects collected including 0 cluster objects from 0 clusters)
LogGarbage: GC purged 0 objects (175 -> 175)
// Spawn後
LogBlueprintUserMessages: [NewMap_C_2] Spawn
LogGarbage: Collecting garbage   (GCheckForIllegalMarkPendingKill = 1)
LogGarbage: Verbose: 0.006933 ms for Mark Phase (11 Objects To Serialize
LogGarbage: 0.004437 ms for Gather Unreachable Objects (0 objects collected including 0 cluster objects from 0 clusters)
LogGarbage: GC purged 0 objects (177 -> 177)
// Destroy後
LogBlueprintUserMessages: [NewMap_C_2] Destroy
LogGarbage: Collecting garbage   (GCheckForIllegalMarkPendingKill = 1)
LogGarbage: Verbose: 0.006657 ms for Mark Phase (11 Objects To Serialize
LogGarbage: 0.004437 ms for Gather Unreachable Objects (2 objects collected including 0 cluster objects from 0 clusters)
LogGarbage: 0.011645 ms for incrementally unhashing unreachable objects. Items 2 (2/2)
LogGarbage: GC purged 2 objects (177 -> 175)

Spawn前のGC対象のオブジェクトが169から175に増えた
Spawnした後のGC対象のオブジェクトは177。増える量は2で変わらない

  • 増えた6個分のGC対象
// 空のBP
Function         4556
StructProperty   5732
BoolProperty     4383
FloatProperty    3669
ObjectProperty   2818
33145 Objects
// 変数を追加したBP
Function         4557 -> +1
StructProperty   5734 -> +2
BoolProperty     4384 -> +1
FloatProperty    3670 -> +1
ObjectProperty   2819 -> +1
33151 Objects

追加した変数のbool, float, struct, Objectは分かるけど、
もう一個のstructとfunctionはどこから……?

ノードを追加してみた

2018-12-09_01h07_24.png

  • GCログ
// Spawn前
LogGarbage: Collecting garbage   (GCheckForIllegalMarkPendingKill = 1)
LogGarbage: Verbose: 0.008874 ms for Mark Phase (11 Objects To Serialize
LogGarbage: 0.004161 ms for Gather Unreachable Objects (0 objects collected including 0 cluster objects from 0 clusters)
LogGarbage: GC purged 0 objects (187 -> 187)
// Spawn後
LogBlueprintUserMessages: [NewMap_C_2] Spawn
LogGarbage: Collecting garbage   (GCheckForIllegalMarkPendingKill = 1)
LogGarbage: Verbose: 0.006657 ms for Mark Phase (11 Objects To Serialize
LogGarbage: 0.003882 ms for Gather Unreachable Objects (0 objects collected including 0 cluster objects from 0 clusters)
LogGarbage: GC purged 0 objects (189 -> 189)
// Destroy後
LogBlueprintUserMessages: [NewMap_C_2] Destroy
LogGarbage: Collecting garbage   (GCheckForIllegalMarkPendingKill = 1)
LogGarbage: Verbose: 0.006933 ms for Mark Phase (11 Objects To Serialize
LogGarbage: 0.003882 ms for Gather Unreachable Objects (2 objects collected including 0 cluster objects from 0 clusters)
LogGarbage: 0.015806 ms for incrementally unhashing unreachable objects. Items 2 (2/2)
LogGarbage: GC purged 2 objects (189 -> 187)

Spawn前のGC対象のオブジェクトが175から187に増えた
Spawnした後のGC対象のオブジェクトは189。増える量は変わらない

  • 増えた12個分のGC対象
// 変数を追加したBP
Function         4557
StructProperty   5734
FloatProperty    3670
IntProperty      1748
33151 Objects
// ノードを追加したBP
Function         4559 -> +2
StructProperty   5735 -> +1
FloatProperty    3678 -> +8
IntProperty      1749 -> +1
33163 Objects

Function 2つはAddとSetFloat?
Float 8つは[New Ver 1]ノード、 [DeltaSeconds]ピン、AddノードのOutputピン*6?
StructとIntが増えたのは何?

マクロ化してみた

2018-12-09_04h49_29.png

  • GCログ
// Spawn前
LogGarbage: Collecting garbage   (GCheckForIllegalMarkPendingKill = 1)
LogGarbage: Verbose: 0.007488 ms for Mark Phase (11 Objects To Serialize
LogGarbage: 0.004437 ms for Gather Unreachable Objects (0 objects collected including 0 cluster objects from 0 clusters)
LogGarbage: GC purged 0 objects (187 -> 187)
// Spawn後
LogBlueprintUserMessages: [NewMap_C_2] Spawn
LogGarbage: Collecting garbage   (GCheckForIllegalMarkPendingKill = 1)
LogGarbage: Verbose: 0.009980 ms for Mark Phase (11 Objects To Serialize
LogGarbage: 0.004716 ms for Gather Unreachable Objects (0 objects collected including 0 cluster objects from 0 clusters)
LogGarbage: GC purged 0 objects (189 -> 189)
// Destroy後
LogBlueprintUserMessages: [NewMap_C_2] Destroy
LogGarbage: Collecting garbage   (GCheckForIllegalMarkPendingKill = 1)
LogGarbage: Verbose: 0.009704 ms for Mark Phase (11 Objects To Serialize
LogGarbage: 0.004712 ms for Gather Unreachable Objects (2 objects collected including 0 cluster objects from 0 clusters)
LogGarbage: 0.012200 ms for incrementally unhashing unreachable objects. Items 2 (2/2)
LogGarbage: GC purged 2 objects (189 -> 187)

ノード単品の時と一緒

マクロの数を増やしてみた

繋げているマクロを3つから5つに増やしてみた

// Spawn前LogGarbage: Collecting garbage   (GCheckForIllegalMarkPendingKill = 1)
LogGarbage: Verbose: 0.006657 ms for Mark Phase (11 Objects To Serialize
LogGarbage: 0.004988 ms for Gather Unreachable Objects (0 objects collected including 0 cluster objects from 0 clusters)
LogGarbage: GC purged 0 objects (191 -> 191)

4つ増えた。Floatピン2つ×マクロ2つ分

関数化してみる

2018-12-09_05h12_14.png

  • GCログ
// Spawn前
LogGarbage: Collecting garbage   (GCheckForIllegalMarkPendingKill = 1)
LogGarbage: Verbose: 0.008039 ms for Mark Phase (11 Objects To Serialize
LogGarbage: 0.005268 ms for Gather Unreachable Objects (0 objects collected including 0 cluster objects from 0 clusters)
LogGarbage: GC purged 0 objects (184 -> 184)
// Spawn後
LogBlueprintUserMessages: [NewMap_C_2] Spawn
LogGarbage: Collecting garbage   (GCheckForIllegalMarkPendingKill = 1)
LogGarbage: Verbose: 0.011925 ms for Mark Phase (11 Objects To Serialize
LogGarbage: 0.003606 ms for Gather Unreachable Objects (0 objects collected including 0 cluster objects from 0 clusters)
LogGarbage: GC purged 0 objects (186 -> 186)
// Destroy後
LogBlueprintUserMessages: [NewMap_C_2] Destroy
LogGarbage: Collecting garbage   (GCheckForIllegalMarkPendingKill = 1)
LogGarbage: Verbose: 0.006098 ms for Mark Phase (11 Objects To Serialize
LogGarbage: 0.004437 ms for Gather Unreachable Objects (2 objects collected including 0 cluster objects from 0 clusters)
LogGarbage: 0.011370 ms for incrementally unhashing unreachable objects. Items 2 (2/2)
LogGarbage: GC purged 2 objects (186 -> 184)

マクロに比べて、ベースが187から184に減った

  • 減った3個分のGC対象
// 変数を追加したBP or マクロ化BP
Function          4559
FloatProperty     3678
33163 Objects
// 関数化BP
Function          4560 -> +1
FloatProperty     3674 -> -4
33160 Objects

別々のノードだったFloatが減って、新規作成したFunction分が増えた
マクロ内のノードは別々のノードとして扱われて、関数内のノードは同一ノードとみなされてPropertyが減る

関数の数を増やした場合

繋げている関数を3つから5つに増やしてみた

// Spawn前
LogGarbage: Collecting garbage   (GCheckForIllegalMarkPendingKill = 1)
LogGarbage: Verbose: 0.008043 ms for Mark Phase (11 Objects To Serialize
LogGarbage: 0.004161 ms for Gather Unreachable Objects (0 objects collected including 0 cluster objects from 0 clusters)
LogGarbage: GC purged 0 objects (184 -> 184)

GC対象の数は変わらない

BPのGC対象が増えるタイミング

2018-12-09_17h28_22.png

上記のようにSoftReferenceにしてBPのロードを明示化

  • GCログ
// ロード前
LogGarbage: Collecting garbage   (GCheckForIllegalMarkPendingKill = 1)
LogGarbage: Verbose: 0.006378 ms for Mark Phase (11 Objects To Serialize
LogGarbage: 0.005826 ms for Gather Unreachable Objects (0 objects collected including 0 cluster objects from 0 clusters)
LogGarbage: GC purged 0 objects (173 -> 173)
// ロード後、Spawn前
LogGarbage: Collecting garbage   (GCheckForIllegalMarkPendingKill = 1)
LogGarbage: Verbose: 0.006653 ms for Mark Phase (11 Objects To Serialize
LogGarbage: 0.003882 ms for Gather Unreachable Objects (0 objects collected including 0 cluster objects from 0 clusters)
LogGarbage: GC purged 0 objects (195 -> 195)
// Spawn後
LogGarbage: Collecting garbage   (GCheckForIllegalMarkPendingKill = 1)
LogGarbage: Verbose: 0.009704 ms for Mark Phase (11 Objects To Serialize
LogGarbage: 0.003882 ms for Gather Unreachable Objects (0 objects collected including 0 cluster objects from 0 clusters)
LogGarbage: GC purged 0 objects (197 -> 197)
// Destroy後
LogGarbage: Collecting garbage   (GCheckForIllegalMarkPendingKill = 1)
LogGarbage: Verbose: 0.010535 ms for Mark Phase (11 Objects To Serialize
LogGarbage: 0.004161 ms for Gather Unreachable Objects (2 objects collected including 0 cluster objects from 0 clusters)
LogGarbage: 0.012476 ms for incrementally unhashing unreachable objects. Items 2 (2/2)
LogGarbage: GC purged 2 objects (197 -> 195)

BPアセットをロードしたタイミングで、BPの変数、ロジックに使用されているプロパティ系列が生成されてGC対象に追加されている

まとめ

今回の検証分の範囲、でのまとめになります

  • BP内の変数/関数等ノードはSpawn時のGCに影響しない
    • よって、1個Spawnしようが100個Spawnしようが変動しない
  • Spawn時にGC対象が増えるのは、Actor、Component。
    • 大量にSpawnする必要がある場合は、Componentを纏めた方がいい
      • 50個のComponentで100体出現すると5000個のGCオブジェクトに
  • 変数、関数、ノード(Outputピン?)がアセットとしてのGC対象になる
  • マクロを使うと、内部のノードが展開される都合上、ノードのGC対象が増える
    • 使用箇所が複数ある場合は関数を使った方がGC的に良い
  • GCコストが高くてどうしてもGC対象を削りたい場合
    • 変数、関数、ロジックをC++に持っていく。GC対象の数が減るので検索コストは下がりそう
      • その場合はUPROPERTYは付けたら駄目(のハズ)
    • 使わないBPアセットとかをロードしない
    • Cluster化したら多分Actor単位での検索になるので楽になるはず(今回は未検証
  • アセットロード/Spawn/Destroyが無ければ(UE4内部的にも)、GC対象や削除対象は増減しない
    • 新規Level+GameModeBaseで放置していてもGC対象の数は勝手に増えない
    • 音ゲーとかカクついたらアウトなシーンは注意

常駐化するテクスチャとかパーティクルとかをGC対象から除外する方法ないのかな……
gc.MaxObjectsNotConsideredByGCはPreInit時点っぽいし

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