2. Memory Management for Android Apps
Patrick Dubroy (dubroy.com · @dubroy)
May 11, 2011

3. 3
192MB RAM

4. 4
1GB RAM

5. 5
G1
320x480
Xoom
1280x800

6. 6

7. 7
Work expands
to fill the time available.
Software
memory

8. Overview
• Changes in Gingerbread and Honeycomb
– heap size
– GC
– bitmaps
• Understanding heap usage
– logs
– memory leaks
– Eclipse Memory Analyzer (MAT)
8

9. Expectations
• Android
• Dalvik heap
• Garbage collection
• OutOfMemoryError
9

10. Heap Size
• Heap size limits
– G1: 16MB
– Droid: 24MB
– Nexus One: 32MB
– Xoom: 48MB
• ActivityManager.getMemoryClass()
10

11. Large Heaps
• Honeycomb adds “largeHeap” option in AndroidManifest.xml:
– Degrades performance! Use only if you understand why you need it.
<application
android:name="com.example.foobar"
android:largeHeap="true"
...
</application>
ActivityManager.getLargeMemoryClass()
11

12. Garbage Collection
12
GC Roots

13. Garbage Collection
13
GC Roots

14. Garbage Collection
14
GC Roots

15. Garbage Collection
15
GC Roots

16. Garbage Collection
• Bigger heaps = longer pauses?
• Pre-Gingerbread GC:
– Stop-the-world
– Full heap collection
– Pause times often > 100ms
• Gingerbread and beyond:
– Concurrent (mostly)
– Partial collections
– Pause times usually < 5ms
16

17. Bitmaps
Old way (pre-Honeycomb):
–freed via recycle() or finalizer
–hard to debug
–full, stop-the-world GCs
17
Managed
Native

18. Bitmaps
Old way (pre-Honeycomb):
–freed via recycle() or finalizer
–hard to debug
–full, stop-the-world GCs
New way:
–freed synchronously by GC
–easier to debug
–concurrent & partial GCs
18
Managed
Native

19. Overview
• Changes in Gingerbread and Honeycomb
– heap size
– GC
– bitmaps
• Understanding heap usage
– logs
– memory leaks
– Eclipse Memory Analyzer (MAT)
19

20. Overview
• Changes in Gingerbread and Honeycomb
– heap size
– GC
– bitmaps
• Understanding heap usage
– logs
– memory leaks
– Eclipse Memory Analyzer (MAT)
20

21. D/dalvikvm( 9050): GC_CONCURRENT freed 2049K, 65% free 3571K/
9991K, external 4703K/5261K, paused 2ms+2ms
Interpreting Log Messages
21

22. Interpreting Log Messages
D/dalvikvm( 9050): GC_CONCURRENT freed 2049K, 65% free 3571K/
9991K, external 4703K/5261K, paused 2ms+2ms
• Reason for GC
– GC_CONCURRENT
– GC_FOR_MALLOC
– GC_EXTERNAL_ALLOC
– GC_HPROF_DUMP_HEAP
– GC_EXPLICIT
22

23. Interpreting Log Messages
D/dalvikvm( 9050): GC_CONCURRENT freed 2049K, 65% free 3571K/
9991K, external 4703K/5261K, paused 2ms+2ms
• Reason for GC
• Amount freed
23

24. Interpreting Log Messages
D/dalvikvm( 9050): GC_CONCURRENT freed 2049K, 65% free 3571K/
9991K, external 4703K/5261K, paused 2ms+2ms
• Reason for GC
• Amount freed
• Heap statistics
24

25. Interpreting Log Messages
D/dalvikvm( 9050): GC_CONCURRENT freed 2049K, 65% free 3571K/
9991K, external 4703K/5261K, paused 2ms+2ms
• Reason for GC
• Amount freed
• Heap statistics
• External memory statistics
25

26. Interpreting Log Messages
D/dalvikvm( 9050): GC_CONCURRENT freed 2049K, 65% free 3571K/
9991K, external 4703K/5261K, paused 2ms+2ms
• Reason for GC
• Amount freed
• Heap statistics
• External memory statistics
• Pause time
26

27. Heap Dumps
• Binary dump of all objects
• Create with:
– DDMS
– android.os.Debug.dumpHprofData()
• Convert to standard HPROF format:
hprof-conv orig.hprof converted.hprof
• Analyze with MAT, jhat, etc.
27

28. Memory Leaks
• GC does not prevent leaks!
• Leak: ref to an unused object preventing GC
• References to Activity (Context)
– View, Drawable, ...
28

29. Memory Leaks
29
Activity
ViewGroup
Views

30. Eclipse Memory Analyzer (MAT)
• Download from http://eclipse.org/mat/
• “Shallow heap” and “retained heap”
30
100
100
100 100

31. Eclipse Memory Analyzer (MAT)
• Download from http://eclipse.org/mat/
• “Shallow heap” and “retained heap”
31
100
100
100 100
R = 100

32. Eclipse Memory Analyzer (MAT)
• Download from http://eclipse.org/mat/
• “Shallow heap” and “retained heap”
32
100
100 100
100
R = 100

33. Eclipse Memory Analyzer (MAT)
• Download from http://eclipse.org/mat/
• “Shallow heap” and “retained heap”
33
100
100
100 100
R = 400

34. Dominator Tree
• Dominator: closest object on every path to node
34
A
B
C E
D
A
B C D
E

35. Demo: Debugging a memory leak with MAT

36. public class MainActivity extends Activity implements ActionBar.TabListener {
static Leaky leak = null;
class Leaky {
void doSomething() {
System.out.println("Wheee!!!");
}
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if (leak == null) {
leak = new Leaky();
}
...
36

37. public class MainActivity extends Activity implements ActionBar.TabListener {
static Leaky leak = null;
class Leaky {
void doSomething() {
System.out.println("Wheee!!!");
}
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if (leak == null) {
leak = new Leaky();
}
...
37

38. public class MainActivity extends Activity implements ActionBar.TabListener {
static Leaky leak = null;
class Leaky {
void doSomething() {
System.out.println("Wheee!!!");
}
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if (leak == null) {
leak = new Leaky();
}
...
38

39. public class MainActivity extends Activity implements ActionBar.TabListener {
static Leaky leak = null;
class Leaky {
void doSomething() {
System.out.println("Wheee!!!");
}
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if (leak == null) {
leak = new Leaky();
}
...
39

40. 40
MainActivity
Leaky
MainActivity
class

41. Demo: Debugging a memory leak with MAT

42. Memory Leaks
• References to Activity, Context, View, Drawable, ...
• Non-static inner classes (e.g. Runnable)
• Caches
42

43. Links
• Articles on Android Developers Blog
– Memory Analysis for Android Applications
– Avoiding Memory Leaks by Romain Guy
• Eclipse Memory Analyzer: http://www.eclipse.org/mat/
• Markus Kohlerʼs Java Performance Blog: http://kohlerm.blogspot.com/
• Feedback on this talk:
http://speakermeter.com/talks/memory-management-android
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