Richard Chien
Details in my Android memory usage research
I will introduce from simple to hard, from some usage to details
A know how from first month of my interns in 2017.
For Powerpoint access: Link
● adb shell cat /proc/meminfo RAM info ● adb shell dumpsys meminfo Process info ● adb shell procrank Process info(Java heap only) ● adb shell showmap Very detailed
- MAT
- DDMS
As we all know the Android Framework below, We will focus on the Android Runtime part so as to help analyze memory in our app development.
Let's make a quick look at some of columns
HightTotal：The total sum of physical RAM of address > 860M , can only be used by user.
HightFree：The unused of physical RAM of address > 860M
LowTotal：The sum of RAM which could be used by Kernel, User in RAM
For a 512M RAM, lowTotal = MemTotal
LowFree : the unused by whether kernel or user RAM
lowFree = MemFree in a 512M RAM
The following image shows the dumpsys memory information from an global launched app (D.A.U. about 3M).
To illustrate different meaning in each blocks Click me for more detail
Dalvik Heap：Dalvik allocated RAM of your app
Pss Total includes all allocated memory from Zygote , will be discussed later.
Private Dirty : the most important part of an runtime app because it is only used by your own process. It is only stored in RAM, which means that it cant be page into storage because Android doesn't support swap.
Heap Alloc is the sum of Dalvik and native heap.
This value is greater than PSS total and Private Dirty because process is forked from Zygote, and allowed to share with others.
Private Clean means the ''clean'' memory generated from your code.
Next, let's have a quick comparison between PSS and it's family.
We can conclude from the above picture
PSS is a very useful number because when the PSS for all processes in the system are summed together, that is a good representation for the total memory usage in the system. When a process is killed, the shared libraries that contributed to its PSS will be proportionally distributed to the PSS totals for the remaining processes still using that library. In this way PSS can be slightly misleading, because when a process is killed, PSS does not accurately represent the memory returned to the overall system.
Another more specific example here:
We have 20MB for Private
and 12 MB Shared (Between 4 processes)
PSS = 20 + (12/4) = 23
And Now we start to look at procrank
There are three API within Java to access memory info.
We will not discuss Runtime class because it's different from two others
Despite fast speed in running this API (about 1000 times faster than two others)
but its value differ and fluctuate a lot, which results in hardly precision.
Ways to show memory by Activity Manager:
void getMemoryInfo(ActivityManager.MemoryInfo outInfo)
Debug.MemoryInfo getProcessMemoryInfo(int[ ] pids)
List<ActivityManager.RunningAppProcessInfo>getRunningAppProcess()
List<ActivityManager.RunningTaskInfoo>getRunningTasks(int maxNum)
Void killBackgroundProcess(String packageName)
Detailed implementation:
private static final class ActivityManagerMemoryGetter implements MemoryGetter {
private final ActivityManager activityManager = (ActivityManager) Globals.getInstance().getSystemService(Context.ACTIVITY_SERVICE);
private final int[] pids = new int[]{Process.myPid()};
private Debug.MemoryInfo info;
@Override
public void refresh() {
Debug.MemoryInfo[] infos = activityManager.getProcessMemoryInfo(pids);
info = infos[0];
}
@Override
public long getDalvikPrivateDirty() {
return info.dalvikPrivateDirty;
}
}
private static final class DebugMemoryGetter implements MemoryGetter {
private Debug.MemoryInfo info;
@Override
public void refresh() {
info = new Debug.MemoryInfo();
Debug.getMemoryInfo(info);
}
@Override
public long getDalvikPrivateDirty() {
return info.dalvikPrivateDirty;
}
}
Speed Comparison
The following image shows the time taken to finish two memory getter above.
we can see that ActivityManager is slightly slower than Debug
Next, we compare the output memory usage value differ.
we can see that both API are used to have same value when APP is running with non-dramatic burst
(simple click on an button without page or context change)
However, when there's a dramatic burst on memory (for method like start camera, activity...)
the value gets different.
Hence as a conclusion, there two API are used in several auto-run memory checker
Determining which to use totally depends on demand.
some argue that Activity manager is developed better and has a better performance
but Debug seems to hit the bull's-eye.
Feel free to contact me if you need Memory auto-dumping source code. (Java)