Android Memory Usage
The memory of an Android system is managed by several different allocators, in several different pools.
- 1 System Memory
- 2 Process Memory
- 3 Dalvik Heap
- 4 Debugging Android application memory usage
- 5 References
You can examine the system's view of the memory on the machine, by examining /proc/meminfo.
If you use 'ddms', you can see a summary of the memory used on the machine, by the system and by the different executing processes. Click on the SysInfo tab, and select "Memory Usage" in the box on the upper left of the pane.
Here's a screenshot:
Note that you can get the numbers for each process by hovering your mouse over a particular pie slice. Numbers are shown in K and percentages.
You can see an individual process' memory usage by examining
Details about memory usage are in
The 'top' command will show VSS and RSS.
Also, see ddms info above.
procrank will show you a quick summary of process memory utilization. By default, it shows Vss, Rss, Pss and Uss, and sorts by Vss. However, you can control the sorting order.
procrank source is included in system/extras/procrank, and the binary is located in /system/xbin on an android device.
- Vss = virtual set size
- Rss = resident set size
- Pss = proportional set size
- Uss = unique set size
In general, the two numbers you want to watch are the Pss and Uss (Vss and Rss are generally worthless, because they don't accurately reflect a process's usage of pages shared with other processes.)
- Uss is the set of pages that are unique to a process. This is the amount of memory that would be freed if the application was terminated right now.
- Pss is the amount of memory shared with other processes, accounted in a way that the amount is divided evenly between the processes that share it. This is memory that would not be released if the process was terminated, but is indicative of the amount that this process is "contributing"
to the overall memory load.
You can also use procrank to view the working set size of each process, and to reset the working set size counters.
Here is procrank's usage:
# procrank -h Usage: procrank [ -W ] [ -v | -r | -p | -u | -h ] -v Sort by VSS. -r Sort by RSS. -p Sort by PSS. -u Sort by USS. (Default sort order is PSS.) -R Reverse sort order (default is descending). -w Display statistics for working set only. -W Reset working set of all processes. -h Display this help screen.
And here is some sample output:
# procrank PID Vss Rss Pss Uss cmdline 1217 36848K 35648K 17983K 13956K system_server 1276 32200K 32200K 14048K 10116K android.process.acore 1189 26920K 26920K 9293K 5500K zygote 1321 20328K 20328K 4743K 2344K android.process.media 1356 20360K 20360K 4621K 2148K com.android.email 1303 20184K 20184K 4381K 1724K com.android.settings 1271 19888K 19888K 4297K 1764K com.android.inputmethod.latin 1332 19560K 19560K 3993K 1620K com.android.alarmclock 1187 5068K 5068K 2119K 1476K /system/bin/mediaserver 1384 436K 436K 248K 236K procrank 1 212K 212K 200K 200K /init 753 572K 572K 171K 136K /system/bin/rild 748 340K 340K 163K 152K /system/bin/sh 751 388K 388K 156K 140K /system/bin/vold 1215 148K 148K 136K 136K /sbin/adbd 757 352K 352K 117K 92K /system/bin/dbus-daemon 760 404K 404K 104K 80K /system/bin/keystore 759 312K 312K 102K 88K /system/bin/installd 749 288K 288K 96K 84K /system/bin/servicemanager 752 244K 244K 71K 60K /system/bin/debuggerd
In this example, it shows that the native daemons and programs are an order of magnitude smaller than the Dalvik-based services and programs. Also, even the smallest Dalvik program requires about 1.5 meg (Uss) to run.
You can see very detailed per-process or systemwide memory information with smem.
The Dalvik heap is preloaded with classes and data by zygote (loading over 1900 classes as of Android version 2.2). When zygote forks to start an android application, the new application gets a copy-on-write mapping of this heap. As Dan Borstein says below, this helps with memory reduction as well as application startup time.
Dalvik, like virtual machines for many other languages, does garbage collection on the heap. There appears to be a separate thread (called the HeapWorker) in each VM process that performs the garbage collection actions. (See toolbox ps -t) [need more notes on the garbage collection]
Dan Borstein said this about heap sharing:
It's used in Android to amortize the RAM footprint of the large amount of effectively-read-only data (technically writable but rarely actually written) associated with common library classes across all active VM processes. 1000+ classes get preloaded by the system at boot time, and each class consumes at least a little heap for itself, including often pointing off to a constellation of other objects. The heap created by the preloading process gets shared copy-on-write with each spawned VM process (but again doesn't in practice get written much). This saves hundreds of kB of dirty unpageable RAM per process and also helps speed up process startup.
[INFO NEEDED: how to show dalvik heap info?]
Debugging Android application memory usage
See an excellent article by Dianne Hackborn at: http://stackoverflow.com/questions/2298208/how-to-discover-memory-usage-of-my-application-in-android/2299813#2299813
How to debug native process memory allocations
setprop dalvik.vm.checkjni true setprop libc.debug.malloc 10 setprop setprop dalvik.vm.jniopts forcecopy start stop
The C library (bionic) in the system supports the ability to utilize a different, debug, version of the malloc code at runtime in the system.
If the system property libc.debug.malloc has a value other than 0, then when a process is instantiated, the C library uses functions for allocating and freeing memory, for that process.
(Note that there are other ways that the debug shared library malloc code ends up being used as well. That is, if you are running in the emulator, and the value of the system property ro.kernel.memcheck is not '0', then you get a debug level of 20. Note that debug level 20 can only be used in the emulator.)
By default, the standard malloc/free/calloc/realloc/memalign routines are used. By setting libc.debug.malloc, different routines are used, which check for certain kinds of memory errors (such as leaks and overruns). This is done by loading a separate shared library (.so) with these different routines.
The shared libraries are named: /system/lib/libc_malloc_debug_leak.so and /system/lib/libc_malloc_debug_qemu.so
(Information was obtained by looking at
Supported values for libc.debug.malloc (debug level values) are:
- 1 - perform leak detection
- 5 - fill allocated memory to detect overruns
- 10 - fill memory and add sentinels to detect overruns
- 20 - use special instrumented malloc/free routines for the emulator
I'm not sure whether these shared libraries are shipped in production devices.