Virtual memory leak while using bitmap

[VEDANTDOKANIA]

When i am using bitmap and as we set the bits in bitmap virtual memory shoots up (verified using pmap command) , but after clearing the bitmap using "bitmap.clear" virtual memory does not releases. I want to know the method to clear bitmap along with all it's instance and used bytes in virtual memory.Memory allocation before using bitmap and after clearing bitmap should be same. Can you pls help me in achieving the same ..