Question

I’m currently looking at the output of the Monotouch memory profiler while running my app in the Simulator.
I can see these numbers:

Object count: 154.043
Total memory: 5.099.648 bytes

Does the “total memory” mean, I’m occupying about 5MB of RAM? Instruments is showing me that about 30MB are allocated, that’s why I’m asking.

Answer 1

Total memory is the amount of memory used by all the managed objects. The profiler just adds up the memory used by each object.

This is not the total amount of memory used in the process, for a couple of reasons:

• MonoTouch doesn’t allocate memory on a per-object basis. MonoTouch allocates memory in chunks instead, and when a new object is created, it will usually be allotted memory already allocated. In any case this is usually a difference you can ignore between the total memory the profiler reports and the real amount of memory your app uses (and it is not the reason for the difference between 5MB of managed memory used and the 30MB Instruments reports).

• MonoTouch (and therefore its profiler) does not know about any memory allocated by native code. If you for instance create an UIImage, the image data is kept entirely in native code, and it won’t show up in our profiler (you will see UIImage instances in the profiler, but the memory used by each will be the managed memory used, which doesn’t include the image data). Another example is if you load a view from a xib: if you don’t access the tree of objects from managed code somehow, no managed objects will be created for any of the objects in the tree, and nothing will show up in the managed profiler. This is the real difference between the 5MB from the managed profiler and the 30MB Instruments reports.

Also have in mind that MonoTouch itself will use more memory in the simulator than on device, since on the simulator it’s been tuned to compile fast (to make debugging as fast as possible), while on device it’s tuned for better runtime performance.