Talking Trash: The Evolution of Garbage Collection on Android

1.

Talking Trash @chethaase & @romainguy

2.

“Garbage in, garbage out”

3.

“Garbage in, garbage out” But how fast?

4.

Modern Android Development Chet Haase @chethaase Romain Guy @romainguy

5.

Modern Android Development Chet Haase @chethaase Romain Guy @romainguy

6.

Modern Android Development Chet Haase @chethaase Romain Guy @romainguy Blah
blah blah memory blah blah...

7.

Optimized for size   |   +- JIT optimizations not
  | as powerful   |   +- Allocation/collection slow   |   +- Heap fragmentation Dalvik

8.

So: _ Avoid allocation whenever possible > For example: enums
_ Primitive types are cool   (autoboxing is not)

9.

ART Optimized for performance JIT + AOT Faster allocation/collection Heap
defragmentation Large object heap

10.

defragmentation Large object heap So:

11.

defragmentation Large object heap So: Allocate as necessary (yes, even enums) Use appropriate types But: phones are still constrained batteries are, too be aware of inner-loop bottlenecks

12.

Memories int foo = 5; MyObject thing = new MyObject();

13.

Memories Stack int foo = 5; MyObject thing = new
MyObject();

14.

Memories Stack Registers int foo = 5; MyObject thing =
new MyObject();

15.

new MyObject(); foo

16.

new MyObject(); foo

17.

new MyObject(); Heap foo

18.

new MyObject(); Heap foo thing

19.

Manual Garbage Collection MyObject* thing = new MyObject; // code
using thing... delete thing; // code using thing C++

20.

using thing... delete thing; // code using thing Leak! C++

21.


22.


23.

using thing... delete thing; // code using thing Crash! C++

24.

using thing... delete thing; // code using thing Crash! C++ (maybe)

25.

Automatic Garbage Collection MyObject thing = new MyObject(); // code
using thing… Java

26.

using thing… No leak! Java // eventually freed

27.

using thing… No leak! Java // eventually freed // code using thing…

28.

using thing… No leak! No crash! Java // eventually freed // code using thing…

29.

Runtime GC Concerns

30.

Runtime GC Concerns How long does allocation take?

31.

Runtime GC Concerns How long does allocation take?   How
long does collection take?

32.

long does collection take? What impact does this have across all threads?

33.

long does collection take? What impact does this have across all threads? When do collections happen?

34.

long does collection take? What impact does this have across all threads? When do collections happen?   How efﬁcient is heap usage?

35.

Dalvik GC ? Allocation

36.


37.


38.

Dalvik GC Allocation

39.

Dalvik GC Collection

40.

Dalvik GC Collection Mark root set (pause)

41.

Dalvik GC Collection Mark root set (pause) Mark reachable I
(concurrent)

42.

(concurrent)

43.

(concurrent) Mark reachable II (pause)

44.

(concurrent) Mark reachable II (pause)

45.

(concurrent) Mark reachable II (pause) Collect (concurrent)

46.

Dalvik GC ? Allocation, Take II

47.


48.


49.

Collection: GC_FOR_ALLOC Dalvik GC ?

50.

Collection: GC_FOR_ALLOC Dalvik GC ?

51.

Allocation Dalvik GC ?

52.

Allocation Dalvik GC

53.

Dalvik GC ? Allocation, Take III

54.

Dalvik GC ? Allocation, Take III

55.

Dalvik GC ? Grow the Heap

56.

Dalvik GC ? Out of Memory Error Grow the Heap
or…

57.

Fragmentation! (Kitkat) Heap

58.


59.


60.


61.


62.


63.

Fragmentation! (Kitkat) Heap ?

64.

Fragmentation! (Kitkat) Heap ?

65.

D/dalvikvm: GC_FOR_ALLOC freed 2K, 50% free 197613K/392536K, paused 6ms, total
6ms I/dalvikvm-heap: Forcing collection of SoftReferences for 2000012-byte allocation D/dalvikvm: GC_BEFORE_OOM freed 0K, 50% free 197613K/392536K, paused 6ms, total 6ms E/dalvikvm-heap: Out of memory on a 2000012-byte allocation. Sad Logcat

66.


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70.

ART (Lollipop) Faster allocation!   Faster collection!   Faster runtime!

71.

ART Allocation

72.

ART Allocation RosAlloc

73.

ART Allocation RosAlloc Replacement for dlmalloc

74.

ART Allocation RosAlloc Replacement for dlmalloc Thread-local allocations

75.

ART Allocation RosAlloc Replacement for dlmalloc Thread-local allocations Grouped small
allocations, page-aligned large allocations

76.

allocations, page-aligned large allocations Finer-grained locks

77.

allocations, page-aligned large allocations Finer-grained locks 4-5x faster than Dalvik!

78.

allocations, page-aligned large allocations Finer-grained locks 4-5x faster than Dalvik!

79.

ART Allocation

80.

ART Allocation Large object space

81.


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83.


84.

ART Allocation Large object space In Dalvik

85.

ART Allocation Large object space ? In Dalvik

86.

ART Allocation Large object space In ART

87.

ART Allocation Large object space In ART

88.

ART Allocation Large object space Moving collector! In ART

89.

ART Allocation Large object space Moving collector! No more fragmentation!
In ART

90.

In ART * * Eventually

91.

In ART * * Eventually

92.

Fragmentation! (L+) Heap

93.


94.


95.

Fragmentation! (L+) Heap ?

96.

Fragmentation! (L+) Heap ?

97.

Dalvik GC Mark root set (pause) Mark reachable I (concurrent)
Mark reachable II (pause) Collect (concurrent)

98.

~10ms Dalvik GC Mark root set (pause) Mark reachable I
(concurrent) Mark reachable II (pause) Collect (concurrent)

99.

~10ms Mark root set (pause) Mark reachable I (concurrent) Mark
reachable II (pause) Collect (concurrent) ART GC

100.

Mark root set (pause) Mark reachable I (concurrent) Mark reachable
II (pause) Collect (concurrent) ART GC

101.

Mark root set (concurrent) Mark reachable I (concurrent) Mark reachable
II (pause) Collect (concurrent) ART GC

102.

Mark root set (concurrent) Mark reachable I (concurrent) Mark reachable
II (pause) Collect (concurrent) ART GC Faster!

103.

~3ms Mark root set (concurrent) Mark reachable I (concurrent) Mark
reachable II (pause) Collect (concurrent) ART GC Faster!

104.

ART Collection

105.

ART Collection Minor GC

106.

ART Collection Minor GC Fast collection of “young generation”

107.

ART Collection Minor GC Fast collection of “young generation” Temporary
objects less expensive

108.

objects less expensive   Large object heap

109.

objects less expensive   Large object heap Less fragmentation

110.

objects less expensive   Large object heap Less fragmentation Less heap resizing

111.

objects less expensive   Large object heap Less fragmentation Less heap resizing Fewer GC_FOR_ALLOC pauses

112.

objects less expensive   Large object heap Less fragmentation Less heap resizing Fewer GC_FOR_ALLOC pauses   Faster runtime

113.

ART in Marshmallow Optimizing compiler Allocation optimizations

114.

ART in Nougat

115.

ART in Nougat More inlining and optimizations

116.

ART in Nougat More inlining and optimizations

117.

ART in Nougat More inlining and optimizations Allocation

118.

ART in Nougat More inlining and optimizations Allocation Rewritten in
assembly

119.

ART in Nougat More inlining and optimizations Allocation Rewritten in
assembly 10x faster than Dalvik (Kitkat)

120.

ART in Oreo

121.

ART in Oreo Concurrent heap compaction

122.

ART in Oreo Concurrent heap compaction Defragmentation in foreground!

123.

ART in Oreo Concurrent heap compaction Defragmentation in foreground! Less
heap resizing, GC_FOR_ALLOC

124.

heap resizing, GC_FOR_ALLOC

125.

heap resizing, GC_FOR_ALLOC Device-wide memory savings

126.

heap resizing, GC_FOR_ALLOC Device-wide memory savings System and Google Play Services

127.

heap resizing, GC_FOR_ALLOC Device-wide memory savings System and Google Play Services Smaller heaps for all

128.

heap resizing, GC_FOR_ALLOC Device-wide memory savings System and Google Play Services Smaller heaps for all

129.

Concurrent Compaction Heap ... T0 Region T1 Region T2 Region
T3 Region Tn Region ... ...

130.

T3 Region Tn Region ... ... Compaction Phase

131.


132.


133.


134.

ART in Oreo Thread-local bump allocator 70% faster allocations than
Nougat 18x faster than Dalvik (Kitkat)

135.

Concurrent Compaction — Allocation Heap ... T0 Region T1 Region
T2 Region T3 Region Tn Region All-thread Heap ... ...

136.

T2 Region T3 Region Tn Region All-thread Heap ... ...

137.

T2 Region T3 Region Tn Region All-thread Heap ... ... T1 Region Free Pointer

138.


139.


140.


141.


142.


143.

Allocation Improvements

144.

ART in O+

145.

ART in O+ Young generation collections gone in O

146.

ART in O+ Young generation collections gone in O Enabled
in AOSP

147.

ART in O+ Young generation collections gone in O Enabled
in AOSP Watch for that future release…

148.

Object Pools

149.

Object Pools Conventional wisdom

150.

Object Pools Conventional wisdom Reusing objects is faster (saves on
allocation/collection time) 

151.

allocation/collection time)  Actual wisdom

152.

allocation/collection time)  Actual wisdom As of Oreo, synchronized object pools are generally slower

153.

Soooo… What Now? Creating garbage is okay (and so is
collecting it)  Use the types and objects you need Even enums  GC is still overhead But not as critical to avoid as it was in Dalvik Make the right choices for your architecture Avoid overhead in critical sections when possible

154.

Jank Test Autoboxing

155.

Jank Test Autoboxing private Float[] mHolder = new Float[100_000];

156.

Jank Test Autoboxing public void run() { long startTime =
System.currentTimeMillis(); float f = 0f; for (int i = 0; i < mHolder.length; ++i, f += 1.0f) { mHolder[i] = f; } System.out.println("Alloc time = " + (System.currentTimeMillis() - startTime)); } private Float[] mHolder = new Float[100_000];

157.

System.currentTimeMillis(); float f = 0f; for (int i = 0; i < mHolder.length; ++i, f += 1.0f) { mHolder[i] = f; } System.out.println("Alloc time = " + (System.currentTimeMillis() - startTime)); } private Float[] mHolder = new Float[100_000]; I/System.out: Alloc time = 28 D/dalvikvm: GC_FOR_ALLOC freed 2047K, 1% free 337371K/339492K, paused 10ms, total 10ms I/System.out: Alloc time = 29

158.

System.currentTimeMillis(); float f = 0f; for (int i = 0; i < mHolder.length; ++i, f += 1.0f) { mHolder[i] = f; } System.out.println("Alloc time = " + (System.currentTimeMillis() - startTime)); } private Float[] mHolder = new Float[100_000]; I/System.out: Alloc time = 28 D/dalvikvm: GC_FOR_ALLOC freed 2047K, 1% free 337371K/339492K, paused 10ms, total 10ms I/System.out: Alloc time = 29 I/System.out: Alloc time = 3 I/System.out: Alloc time = 2 I/System.out: Alloc time = 4

159.

Jank Test Bitmaps

160.

Jank Test Bitmaps public void run() { long startTime =
System.currentTimeMillis(); mBitmap = Bitmap.createBitmap(1_000, 1_000, Bitmap.Config.ARGB_8888); System.out.println("Alloc time = " + (System.currentTimeMillis() - startTime)); }

161.

System.currentTimeMillis(); mBitmap = Bitmap.createBitmap(1_000, 1_000, Bitmap.Config.ARGB_8888); System.out.println("Alloc time = " + (System.currentTimeMillis() - startTime)); } I/System.out: Alloc time = 16 D/dalvikvm: GC_FOR_ALLOC freed 3907K, 2% free 341280K/347244K, paused 7ms, total 7ms I/dalvikvm-heap: Grow heap (frag case) to 337.165MB for 4000012-byte allocation D/dalvikvm: GC_FOR_ALLOC freed <1K, 1% free 345186K/347244K, paused 7ms, total 7ms

162.

System.currentTimeMillis(); mBitmap = Bitmap.createBitmap(1_000, 1_000, Bitmap.Config.ARGB_8888); System.out.println("Alloc time = " + (System.currentTimeMillis() - startTime)); } I/System.out: Alloc time = 16 D/dalvikvm: GC_FOR_ALLOC freed 3907K, 2% free 341280K/347244K, paused 7ms, total 7ms I/dalvikvm-heap: Grow heap (frag case) to 337.165MB for 4000012-byte allocation D/dalvikvm: GC_FOR_ALLOC freed <1K, 1% free 345186K/347244K, paused 7ms, total 7ms I/System.out: Alloc time = 1 I/System.out: Alloc time = 0 I/System.out: Alloc time = 0 I/System.out: Alloc time = 1

163.

None

164.

data class Float3(x: Float, y: Float, z: Float) fun Tonemap_ACES(x:
Float3): Float3 { val a = 2.51f val b = 0.03f val c = 2.43f val d = 0.59f val e = 0.14f return (x * (a * x + b)) / (x * (c * x + d) + e) }

165.

inline operator fun Float.plus(v: Float3) = Float3(this + v.x, this
+ v.y, this + v.z) inline operator fun Float.times(v: Float3) = Float3(this * v.x, this * v.y, this * v.z)

166.

None

167.

None

168.

None

169.

Android O, 1 tile = 00.1~00.5s

170.

Android O, 1 tile = 00.1~00.5s Android K, 1 tile
= 40.0~50.0s

171.

10-23 14:40:04.997 3885-3908/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 712K, 14% free 5124K/5912K,
paused 4ms, total 4ms 10-23 14:40:05.067 3885-3908/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 712K, 14% free 5124K/5912K, paused 2ms, total 2ms 10-23 14:40:05.147 3885-3901/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 712K, 14% free 5124K/5912K, paused 2ms, total 2ms 10-23 14:40:05.177 3885-3907/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 712K, 14% free 5124K/5912K, paused 5ms, total 5ms 10-23 14:40:05.207 3885-3909/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 712K, 14% free 5124K/5912K, paused 3ms, total 3ms 10-23 14:40:05.277 3885-3903/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 712K, 14% free 5124K/5912K, paused 2ms, total 2ms 10-23 14:40:05.307 3885-3909/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 712K, 14% free 5125K/5912K, paused 3ms, total 3ms 10-23 14:40:05.357 3885-3901/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 713K, 14% free 5124K/5912K, paused 5ms, total 5ms 10-23 14:40:05.397 3885-3903/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 712K, 14% free 5124K/5912K, paused 3ms, total 3ms 10-23 14:40:05.447 3885-3901/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 712K, 14% free 5124K/5912K, paused 2ms, total 2ms 10-23 14:40:05.517 3885-3902/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 712K, 14% free 5124K/5912K, paused 2ms, total 2ms 10-23 14:40:05.607 3885-3909/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 712K, 14% free 5124K/5912K, paused 2ms, total 2ms 10-23 14:40:05.677 3885-3903/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 712K, 14% free 5124K/5912K, paused 2ms, total 2ms 10-23 14:40:05.707 3885-3909/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 712K, 14% free 5124K/5912K, paused 4ms, total 4ms 10-23 14:40:05.767 3885-3902/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 712K, 14% free 5124K/5912K, paused 2ms, total 2ms 10-23 14:40:05.837 3885-3908/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 712K, 14% free 5124K/5912K, paused 2ms, total 2ms 10-23 14:40:05.867 3885-3902/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 712K, 14% free 5124K/5912K, paused 2ms, total 2ms 10-23 14:40:05.897 3885-3901/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 712K, 14% free 5124K/5912K, paused 2ms, total 2ms 10-23 14:40:05.957 3885-3902/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 712K, 14% free 5124K/5912K, paused 5ms, total 5ms 10-23 14:40:05.997 3885-3902/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 712K, 14% free 5124K/5912K, paused 2ms, total 2ms 10-23 14:40:06.037 3885-3908/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 712K, 14% free 5124K/5912K, paused 2ms, total 2ms 10-23 14:40:06.107 3885-3908/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 712K, 14% free 5124K/5912K, paused 2ms, total 2ms 10-23 14:40:06.157 3885-3902/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 712K, 14% free 5124K/5912K, paused 3ms, total 3ms 10-23 14:40:06.227 3885-3909/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 712K, 14% free 5124K/5912K, paused 4ms, total 4ms 10-23 14:40:06.267 3885-3901/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 712K, 14% free 5124K/5912K, paused 3ms, total 3ms 10-23 14:40:06.337 3885-3903/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 712K, 14% free 5124K/5912K, paused 2ms, total 2ms 10-23 14:40:06.367 3885-3907/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 712K, 14% free 5124K/5912K, paused 2ms, total 2ms 10-23 14:40:06.437 3885-3901/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 712K, 14% free 5124K/5912K, paused 5ms, total 5ms 10-23 14:40:06.527 3885-3909/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 712K, 14% free 5124K/5912K, paused 2ms, total 2ms 10-23 14:40:06.597 3885-3907/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 712K, 14% free 5124K/5912K, paused 4ms, total 4ms 10-23 14:40:06.617 3885-3901/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 712K, 14% free 5124K/5912K, paused 4ms, total 4ms 10-23 14:40:06.697 3885-3909/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 712K, 14% free 5124K/5912K, paused 2ms, total 2ms 10-23 14:40:06.717 3885-3902/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 712K, 14% free 5124K/5912K, paused 2ms, total 2ms 10-23 14:40:06.767 3885-3901/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 712K, 14% free 5124K/5912K, paused 2ms, total 2ms 10-23 14:40:06.817 3885-3901/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 713K, 14% free 5124K/5912K, paused 3ms, total 3ms 10-23 14:40:06.857 3885-3907/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 711K, 14% free 5124K/5912K, paused 5ms, total 5ms 10-23 14:40:06.937 3885-3908/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 712K, 14% free 5124K/5912K, paused 5ms, total 5ms 10-23 14:40:06.957 3885-3901/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 712K, 14% free 5124K/5912K, paused 2ms, total 2ms 10-23 14:40:07.027 3885-3903/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 712K, 14% free 5124K/5912K, paused 2ms, total 2ms 10-23 14:40:07.117 3885-3907/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 712K, 14% free 5124K/5912K, paused 2ms, total 2ms 10-23 14:40:07.157 3885-3901/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 712K, 14% free 5124K/5912K, paused 2ms, total 2ms 10-23 14:40:07.197 3885-3909/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 712K, 14% free 5124K/5912K, paused 5ms, total 5ms 10-23 14:40:07.257 3885-3908/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 712K, 14% free 5124K/5912K, paused 2ms, total 2ms 10-23 14:40:07.307 3885-3908/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 712K, 14% free 5124K/5912K, paused 3ms, total 3ms 10-23 14:40:07.357 3885-3908/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 712K, 14% free 5124K/5912K, paused 2ms, total 2ms 10-23 14:40:07.397 3885-3903/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 712K, 14% free 5124K/5912K, paused 3ms, total 3ms 10-23 14:40:07.447 3885-3903/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 712K, 14% free 5124K/5912K, paused 2ms, total 2ms 10-23 14:40:07.477 3885-3908/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 712K, 14% free 5124K/5912K, paused 2ms, total 2ms 10-23 14:40:07.557 3885-3901/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 712K, 14% free 5124K/5912K, paused 2ms, total 2ms 10-23 14:40:07.617 3885-3903/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 712K, 14% free 5124K/5912K, paused 2ms, total 2ms 10-23 14:40:07.647 3885-3908/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 712K, 14% free 5124K/5912K, paused 2ms, total 2ms 10-23 14:40:07.677 3885-3901/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 712K, 14% free 5124K/5912K, paused 5ms, total 5ms 10-23 14:40:07.707 3885-3903/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 712K, 14% free 5124K/5912K, paused 2ms, total 2ms 10-23 14:40:07.727 3885-3901/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 712K, 14% free 5124K/5912K, paused 5ms, total 5ms 10-23 14:40:07.767 3885-3909/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 712K, 14% free 5124K/5912K, paused 2ms, total 2ms 10-23 14:40:07.797 3885-3908/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 712K, 14% free 5124K/5912K, paused 2ms, total 2ms 10-23 14:40:07.847 3885-3907/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 712K, 14% free 5124K/5912K, paused 5ms, total 5ms 10-23 14:40:07.927 3885-3903/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 712K, 14% free 5125K/5912K, paused 5ms, total 5ms 10-23 14:40:08.057 3885-3902/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 713K, 14% free 5124K/5912K, paused 4ms, total 4ms 10-23 14:40:08.077 3885-3907/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 712K, 14% free 5124K/5912K, paused 5ms, total 5ms 10-23 14:40:08.107 3885-3903/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 712K, 14% free 5124K/5912K, paused 2ms, total 2ms 10-23 14:40:08.147 3885-3908/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 712K, 14% free 5124K/5912K, paused 4ms, total 4ms 10-23 14:40:08.207 3885-3901/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 712K, 14% free 5124K/5912K, paused 2ms, total 2ms 10-23 14:40:08.267 3885-3902/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 713K, 14% free 5124K/5912K, paused 4ms, total 4ms 10-23 14:40:08.287 3885-3907/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 711K, 14% free 5124K/5912K, paused 5ms, total 5ms 10-23 14:40:08.337 3885-3902/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 712K, 14% free 5124K/5912K, paused 4ms, total 4ms

172.

10-23 14:40:24.847 3885-3909/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 712K, 14% free 5124K/5912K,
paused 3ms, total 3ms 10-23 14:40:24.917 3885-3903/com.google.ray_trasher D/dalvikvm: GC_FOR_ALLOC freed 712K, 14% free 5124K/5912K, paused 2ms, total 2ms

173.

None

174.

Benchmarks, GC and Caches

175.

Core Core Core Core Kryo 385 (Pixel 3) “Gold” cores

176.

Core Core Core Core L1 L1 L1 L1 Kryo 385
(Pixel 3) 4x 32 KiB “Gold” cores

177.

Core Core Core Core L2 L2 L2 L2 L1 L1
L1 L1 Kryo 385 (Pixel 3) 4x 32 KiB “Gold” cores 4x 256 KiB

178.

Core Core Core Core L2 L2 L2 L2 L3 L1
L1 L1 L1 Kryo 385 (Pixel 3) 4x 32 KiB “Gold” cores 4x 256 KiB 1x 2 MiB

179.

L2 L3 L1 private val data = FloatArray(16) // …
val a = foo[0] RAM

180.

val a = foo[0] RAM

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val a = foo[0] RAM

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val a = foo[0] RAM

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val a = foo[0] RAM

184.

64 bytes

185.

val m = ArrayList<FloatArray>(n) 64 bytes

186.

m[0] = FloatArray(4) m[1] = FloatArray(4) m[2] = FloatArray(4) m[n]
= FloatArray(4) val m = ArrayList<FloatArray>(n) 64 bytes

187.

= FloatArray(4) val m = ArrayList<FloatArray>(n) RAM 64 bytes

188.

m[0] FloatArray(4) m[1] FloatArray(4) m[2] FloatArray(4) m[n] FloatArray(4) val m
= ArrayList<FloatArray>(n) for (i in 0 until m.size - 3) { val a = m[i ] val b = m[i + 1] val c = m[i + 2] val d = m[i + 3] computeStuff(a, b, c, d) } L1 64 bytes

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= FloatArray(4) val m = ArrayList<FloatArray>(n) RAM 64 bytes

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0.0 1.0 2.0 3.0 4.0 5.0 6.0 No thrash L1
thrash L2 thrash Relative computation times (Pixel 3)

205.

On some workloads, the work of the GC will affect
performance

206.

You might be benchmarking perfect memory access patterns

207.

Questions?

Talking Trash: The Evolution of Garbage Collection on Android

Talking Trash: The Evolution of Garbage Collection on Android

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