This document discusses memory management in Android, including: 1) An overview of the Java memory model and garbage collection process in Android, including the heap structure and garbage collector. 2) The java.lang.ref package which contains classes like WeakReference and SoftReference that are used in memory management. 3) Tips for optimizing memory usage in Android such as limiting heap size, using large heap configuration, and analyzing garbage collection logs.

1. Memory
in Android

2. Agenda
• Java Memory Model
• java.lang.ref.*
• Garbage Collector
• Tools
• Android Memory Management Tips
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3. Java Memory Model
Heap
Young Generation
Eden Space
From Space
(Survivor1)
To Space
(Survivor2)
Old/Turned
Generation
Perm
Gen
Thread
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4. … in Android
• Heap size limits
• ActivityManager.getMemoryClass()
• android:largeHeap="true“
• ActivityManager.getLargeMemoryClass()
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5. java.lang.ref.*
•ReferenceQueue
•Reference
•WeakReference
•SoftReference
•PhantomReference
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6. Garbage collection
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Before marking
After marking
After sweeping
Allocator holds a list of
references to free spaces,
and searches for free space
whenever an allocation is
required

7. 7
GC Roots

8. Log Messages
D/dalvikvm:
<GC_Reason>
<Amount_freed>,
<Heap_stats>,
<External_memory_stats>,
<Pause_time>
D/dalvikvm( 9050):
GC_CONCURRENT
freed 2049K,
65% free 3571K/9991K,
external 4703K/5261K,
paused 2ms+2ms
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GC_CONCURRENT
GC_FOR_MALLOC
GC_HPROF_DUMP_HEAP
GC_EXPLICIT
GC_EXTERNAL_ALLOC

9. Tools
Demo
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10. GC Tips
• Know your application
• Read the logs
• Use MAT
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11. Thanks
bandysik@gmail.com
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