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Android Memory"Where is all my RAM"

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Deep Dive Into State Restoration

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+Yossi Elkrief @elkriefy

MaTriXy

Android Group leader Tikal

Proud Father Android developer since 2008 GDG Beer Sheva co-founder & leader Android Mentor @ Google Campus Android Lecturer & speaker LFC fan Androids collector

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Android Memory

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Android MemoryAndroid Memory

• Android does not offer swap space for memory.

• Android’s VM performs routine GC.

• Don’t ignore when and where app allocates and releases memory.

• The only way is analyze app’s memory usage with tools and proper care.

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• The Java heap• The native heap • Android shared memory - ashmem.

Android Memory Regions

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Android Memory Regions• The Java heap per-application limited size by the device

manufacturer. Memory is garbage-collected.

• The native heap used by the C++ new operator.The app is limited only by the physical memory available on the device. There is no garbage collection.

• Android shared memory - ashmem. Android can “unpin” the memory rather than freeing it. This is a lazy free; the memory is freed only if the system actually needs more memory. When Android “pins” the memory back, old data will still be there if it hasn't been freed.

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• android:largeHeap • All processes in application.

• Shared user ID - all must have same Flag.

• Better focus on reducing overall memory usage.

• Does not guarantee a fixed increase in available memory.

Increase Heap size

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Viewing Heap Updates

http://static.tumblr.com/52679116680c197db232c3116ce98537/y07rdrp/1XJmt370e/tumblr_static_demotimeheader2.png

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How Android Manages Memory

• Sharing Memory

• App is Forked from Zygote.

• Zygote starts on system boot , loads

common framework code and resources.

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How Android Manages Memory

• Static data is mmapped into a process. Allows page out when needed.

• Android shares dynamic RAM across

processes using explicitly allocated shared

memory regions.

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How Android Manages Memory

• Restricting App Memory

• Hard limit heap size for each app

• Heap size limit varies between devices

• ActivityManager.getMemoryClass ()

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How Android Manages Memory

• Switching Apps

• Android keeps processes cached

• Least-recently used (LRU) cache

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Memory Leak

• Memory leak is when code has a reference to an object that is no longer needed, preventing the VM to perform the garbage collection for that reference.

• Degradation in performance as the memory consumption increases.

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Memory Leak

• Application tries to exceed the available memory,

• We get Out of Memory.

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Viewing Overall Memory Allocations

• Private RAM

• Clean

• Dirty

• Proportional Set Size (PSS)

adb shell dumpsys meminfo <package_name>

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Private (Clean and Dirty) RAM• Memory that is being used by only your process.

• RAM that the system can reclaim when your app’s process is destroyed.

• Most important portion is “private dirty” RAM - the most expensive.

• Used by only your process and its contents exist only in RAM so can’t be paged to storage.

• Dalvik and native allocations will be private dirty RAM

• Dalvik and native allocations you share with the Zygote process are shared dirty RAM.

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Proportional Set Size (PSS)• Measurement of app’s RAM usage that takes into account sharing pages across

processes.

• RAM pages that are unique to process directly contribute to its PSS value.

• Shared Pages contribute to the PSS value only in proportion to the amount of sharing.

• For example, a page that is shared between two processes will contribute half of its size to the PSS of each process.

• PSS from all processes actual memory usage in device.

• Good Comparison against the RAM use of other processes.

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GC Log Messages

• logcat prints a message every GC (Only on Dalvik):

• ART GC Log message.

• Explicit GC

• GC pause >5ms

• GC duration > 100ms

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Interpreting Log Messages

• D/dalvikvm: <GC_Reason> <Amount_freed>,

<Heap_stats>, <External_memory_stats>,

<Pause_time>

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Interpreting Log Messages

• I/art: <GC_Reason> <GC_Name> <Objects_freed>(<Size_freed>) AllocSpace Objects, <Large_objects_freed>(<Large_object_size_freed>) <Heap_stats> LOS objects, <Pause_time(s)>

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Tracking Allocations• Narrowing down memory issues.

• Better understanding memory-hogging objects allocations.

• Useful to analyze critical code paths.

• For example - flinging a list in your app

• Viewing all the allocations that need to be done for that behaviour.

• What thread they are on.

• Where they came from.

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Tracking Allocations Demo

http://upload.wikimedia.org/wikipedia/commons/8/85/Flickr_-_The_U.S._Army_-_Working_dog_demo.jpg

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References• SoftReference

• WeakReference

• PhantomReference.

• "Weakness" less restrictions on the garbage

collector as to when it is allowed to actually

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References

• SoftReference

• Object is not strongly reachable.

• There is at least one path from the root set to

the object that does traverse a

java.lang.ref.SoftReference.

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References• WeakReference

• Object is neither strongly nor softly

reachable.

• There is at least one path from the root set to

the object that does traverse a

java.lang.ref.WeakReference.

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References• PhantomReference.

• Object is neither strongly, softly, nor weakly

reachable.

• The object is referenced by a

java.lang.ref.PhantomReference instance.

• The object has already been finalized.

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Eclipse Memory Analyser ToolMAT

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Process Stats: Understanding How Your App Uses RAM

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Process Stats

• Available since KitKat

• Settings > Developer options > Process Stats.

• Usage is quite simple.

• Try it out now

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Memory leaks Examples

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• Anonymous Inner Class - keeps a reference to instance of parent.

• Activity leak

• Threads leak

• Handler leak

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Hunting memory leaks• Get an OutOfMemoryError (OOM) crashe/s .

• Attempt to reproduce the problem. You need to figure out what navigation sequence triggers the leak, possibly by brute force.

• Dump the heap when the OOM occurs.

• Poke around the heap dump and find an object that should have been garbage collected.

• Compute the shortest strong reference path from that object to the GC roots.

• Figure out which reference in the path should not exist, and fix the memory leak.

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The story ofLeakCanary

https://corner.squareup.com/2015/05/leak-canary.html

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LeakCanary:Detect all memory leaks!

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LeakCanary

• A memory leak detection library for Android and Java.

• Built by Square

• Easy to integrate

• Full open source project - on Github

• https://github.com/square/leakcanary

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Tips to Go

• Avoid Memory Churn.

• Avoid Objects allocation inside onDraw().

• Keep an eye on your References.

• Avoid Soft References for caching

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• Avoid using non-static inner classes in an activity if

instances of the inner class could outlive the activity's

lifecycle.

• Avoid passing anonymous inner class objects to static / singleton classes which keep a strong reference to it.

• Don’t hold references to activities whenever possible.

Tips to Go

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• Use objects pool - created once and reused.

• Blank activity with very little memory consumption, transition to it and force a GC.

• Use Heap dump.

• Use Allocation Tracker.

before and after the transition.

Tips to Go

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• GC : Don’t call me…

http://memecrunch.com/meme/1C7NB/i-m-not-saying-don-t-call-me/image.jpg

Till next time, Yossi is satisfied

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Thank you!

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Resources• developer.android.com • Multitasking-android-way• process stats

Roboto font.

Inside Techsmith images • Dennis Cornwell Keynote animation and style • Cyril Mottier

https://github.com/MaTriXy/RecyclerviewDemos • Yossi Elkrief