Memory Management in Android
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This document provides an overview of memory management in Android. It begins with an architecture recap and discussion of system startup and memory layout. It then covers the kernel's role in managing physical memory and virtual address spaces. It discusses various kernel interfaces for memory, like memory-mapped registers and DMA. Userspace interfaces like brk and mmap are also covered. Low-memory conditions and the OOM killer are explained. Bionic and malloc/free are summarized. Considerations for app developers around measuring memory usage are provided. Finally, various tools for analyzing memory at the kernel, native, and framework levels are listed.
![App Dev ConsiderationsApp Dev Considerations
Recommendations given by Google
Measuring app mem usage
Getting system mem usage
android.os.Debug
android:largeHeap="true"
https://developer.android.com/training/articles
/memory.html
https://developer.android.com/reference/android
/app/ActivityManager.html#getProcessMemoryInfo%28int[]%29
public MemoryInfo[] getProcessMemoryInfo (int[] pids)
https://developer.android.com/reference/android
/app/ActivityManager.html#getMemoryInfo%28android.app.ActivityManager.MemoryInfo%29
public void getMemoryInfo (ActivityManager.MemoryInfo outInfo)](https://image.slidesharecdn.com/memory-management-internals-151206-151206184437-lva1-app6892/85/Memory-Management-in-Android-19-320.jpg)
![8.1 Kernel8.1 Kernel
Overall memory use
Physical-mapped reg address ranges
FS cache
"fragmentation"
/proc interface
RSS, VSS, USS, PSS, etc.
/proc/[pid]/maps, semantics of](https://image.slidesharecdn.com/memory-management-internals-151206-151206184437-lva1-app6892/85/Memory-Management-in-Android-21-320.jpg)
Memory Management in Android
- 1. Memory ManagementMemory Management in Androidin Android AnDevCon Santa Clara 2015
- 2. CC-BY-SA 3.0 - Attribution requirements and misc., PLEASE READ: This slide must remain as-is in this specific location (slide #1), everything else you are free to change; including the logo :-) Use of figures in other documents must feature the below "Originals at" URL immediately under that figure and the below copyright notice where appropriate. You are FORBIDDEN from using the default "About" slide as-is or any of its contents. Copyright (C) 2014-2015, Opersys inc. These slides created by: Karim Yaghmour Originals at: http://www.opersys.com/training/
- 3. AboutAbout
- 4. Introduced Linux Trace Toolkit in 1999 Originated Adeos and relayfs (kernel/relay.c) Ara Android Arch Oversight Training, Custom Dev, Consulting, ...
- 5. "Note that memory usage on modern operating systems like Linux is an extremely complicated and difficult to understand area. In fact the chances of you actually correctly interpreting whatever numbers you get is extremely low. (Pretty much every time I look at memory usage numbers with other engineers, there is always a long discussion about what they actually mean that only results in a vague conclusion.)" -- Dianne Hackborn, Feb 19, 2010, Stackoverflow
- 6. AgendaAgenda Architecture Recap1. Kernel's overall role2. Kernel driver interfaces3. Kernel user-space interfaces4. Low-memory conditions5. Bionic6. App Dev Considerations7. Tools8. Misc.9. References10.
- 7. Demo HardwareDemo Hardware Nexus 7 (Flo 2013) Qualcomm Snapdragon S4 Pro -- APQ8064 Krait CPU, 4-core, 1.51 GHz, 2MB L2 cache 2 GB on-board DDR3 (PCDDR 533MHz) 16 GB eMMC Combined power/usb
- 8. Architecture RecapArchitecture Recap AOSP System startup Memory layout
- 10. 2. System startup2. System startup
- 11. 3. Memory layout3. Memory layout
- 12. Kernel's overall roleKernel's overall role Manage physical memory Manage virtual-to-physical mappings Process isolation: Protect the hardware from user-space Protect processes from each other Driver capabilities: Memory-mapped registers DMA MTD maps Filesystem cache File mapping Swapping
- 13. InternalsInternals Architecture-independent: Architecture-specific: Per-task struct (include/linux/sched.h): The memory structures (include/linux/mm_types.h): mm/ arch/arm/mm/ struct task_struct { ... struct mm_struct *mm, *active_mm; ... struct mm_struct { struct vm_area_struct * mmap; /* list of VMAs */ struct rb_root mm_rb; struct vm_area_struct * mmap_cache; /* last find_vma result */
- 14. Kernel driver interfacesKernel driver interfaces Memory-mapped registers DMA MTD maps ION
- 15. Kernel user-space interfacesKernel user-space interfaces brk mmap/munmap
- 16. Low-memory conditionsLow-memory conditions OOM killer oom_adj Android low-mem driver oom_adj set during init Modifications to oom_adj at runtime by framework
- 17. BionicBionic malloc()/free() Comes from Doug Lea's dlmalloc Public Domain See bionic/libc/upstream-dlmalloc/ Tutorial/doc: Dates back to 1987 Uses CALL_MORECORE() macro do allocations Based on sbrk() dlopen()/dlsym() http://g.oswego.edu/dl/html/malloc.html https://en.wikipedia.org/wiki/C_dynamic_memory_allocation
- 18. Flags to debug/observe malloc/free Linux Enable native monitoring by DDMS: Open ~/.android/ddms.cfg Add line stating: "native=true" $ adb shell setprop libc.debug.malloc 1 $ adb shell stop $ adb shell start
- 19. App Dev ConsiderationsApp Dev Considerations Recommendations given by Google Measuring app mem usage Getting system mem usage android.os.Debug android:largeHeap="true" https://developer.android.com/training/articles /memory.html https://developer.android.com/reference/android /app/ActivityManager.html#getProcessMemoryInfo%28int[]%29 public MemoryInfo[] getProcessMemoryInfo (int[] pids) https://developer.android.com/reference/android /app/ActivityManager.html#getMemoryInfo%28android.app.ActivityManager.MemoryInfo%29 public void getMemoryInfo (ActivityManager.MemoryInfo outInfo)
- 21. 8.1 Kernel8.1 Kernel Overall memory use Physical-mapped reg address ranges FS cache "fragmentation" /proc interface RSS, VSS, USS, PSS, etc. /proc/[pid]/maps, semantics of
- 23. 8.3 Dalvik/ART8.3 Dalvik/ART Heap size measurement API in apps to get access to heap size from Runtime MAT/Eclipse dalvik.vm.heapsize https://developer.android.com /reference/java/lang/Runtime.html#maxMemory%28%29 public long maxMemory ()
- 24. 8.4. Framework8.4. Framework dumpsys meminfo dumpsys procinfo
- 25. Misc.Misc. DDOS on memory KitKat efforts for low-mem Security aspects HAL use of mmap Swap space? zMAP ION CMA
- 26. ReferencesReferences developer.android.com source.android.com strong/weak/soft/phantom references wrt Java GC: - - --> http://source.android.com/devices/native-memory.html http://source.android.com/devices/low-ram.html https://developer.android.com/tools/debugging/debugging-memory.html https://developer.android.com/training/articles/memory.html http://android-developers.blogspot.com/2011/03/memory-analysis- for-android.html http://android-developers.blogspot.com/2009/02/track-memory- allocations.html https://stackoverflow.com/questions/2298208/how-to-discover-memory- usage-of-my-application-in-android http://elinux.org/Android_Memory_Usage https://www.youtube.com/watch?v=_CruQY55HOk http://blog.yojimbocorp.com/2012/10/03/view-android-application-memory- usage-with-eclipse-ddms-plugin/ https://lwn.net/Articles/480055/ https://lwn.net/Articles/565469/ https://weblogs.java.net/blog/2006 /05/04/understanding-weak-references http://docs.oracle.com/javase/7/docs /api/java/lang/ref/package-summary.html