Android :: Android - Image Cache Stategy And Memory Cache Size

I'm implementing an image cache system for caching downloaded image.

My strategy is based upon two-level cache:
Memory-level and disk-level.

My class is very similar to the class used in the droidfu project

My downloaded images are put into an hashmap and the Bitmap objet is wrapped inside a SoftRererence object.

Also every image is saved permanently to the disk.
If a requested image is not found into the Hashmap<String,SoftReference<Bitmap>> it will be searched on the disk, readed, and then pushed back into the hashmap. Otherwise the image will be downloaded from the network.

Since I store the images into the phisical device momery, I have added a check for preserve the device space and stay under a 1M of occupied space:

CODE:.................

This method is called sometime afte a disk writing:

CODE:..............

What I'd like to add is the same check on the HashMap size to prevent it will grow too much. Something like this:

CODE:.....................

My question is:
What could be a right MAX_MEMORY_SIZE value? Also, Is it a good approach? A good answer also could be: "Don't do it! SoftReference is already enough"