Backpack Question

HI,
With all the new baggage rules on size how does this work on backpacks? Reason I ask is my backpack I currently have is just over the size of the hand baggage allowance now. However, unless you ram it totally full of stuff it will easily scrunch down to below the maximum size allowed for hand baggage so should this be OK, or do I have to get a smaller backpack?
Ta!
With all the new baggage rules on size how does this work on backpacks? Reason I ask is my backpack I currently have is just over the size of the hand baggage allowance now. However, unless you ram it totally full of stuff it will easily scrunch down to below the maximum size allowed for hand baggage so should this be OK, or do I have to get a smaller backpack?
Ta!