Android Running apps memory usage

Question

What is the difference between the heap usage (Allocated) we can see in the Elipse Memory Analysis Tool (in the DDMS view) and the memory usage size for the same App shown here on the Android device?:

Settings->Apps->Running

Even though I aggressively tried to preserve memory by making objects null as soon as they weren't needed, the latter number (memory usage size on Running apps screen) only kept increasing and my app finally crashed due to OutOfMemoryError. However, the former showed me that I was well within a reasonable size. I was also calling System.gc() a lot. Is there a difference between the two? Why the discrepancy? Any ideas on how I can solve this problem?

Answer 1

The biggest difference between the two that I know of is the scope of garbage collection.

Normal garbage collection, including System.gc(), collects a bit of garbage, then stops. It is not a complete sweep of the heap to get rid of everything. That is to try to minimize the CPU impact of garbage collection.

The heap dump prepared for MAT, though, effectively a complete GC.

Your symptoms suggest that you are allocating memory faster than GC can reclaim it. The primary solution for this is to try to allocate less memory, or allocate it less frequently. For example, where possible, reuse objects, bitmap buffers, and the like, instead of trying to let GC clean the old stuff and allocating new stuff as you go.

Answer 2

It sounds like you have a memory leak somewhere in your application if the memory is never released. This means that somewhere you are maintaining a strong reference to a large object which is being recreated (like an Activity or Bitmap) which is why calling System.gc() is making no difference.

I suggest watching the following on memory management in android from google IO 2011. It lets you know how to use the eclipse memory analyser tool which is incredibly useful for debugging this sort of error