Q. How can we free the memory by using Boundary tag method in the context of Dynamic memory management?
Ans.
Boundary Tag Method to free Memory is described below
To remove the arbitrary block from the free list (to combine it with the newly made free block) without traversing the whole list, the free list should be doubly linked. Thus each and every free block must contain 2 pointers, next and prev to the next and previous free block on the free block. (This is required when combining a newly freed block with a free block which immediately proceeds in the memory). Thus the front of the free block should be accessible from its rear. One way to do this is to introduce a bsize field at the given offset from the last location or address of each free block. This field exhibits the same value as the size filed at the front of the block. This field have the some value as the size field at the front of the block. The figure below shows the structure of free and allocated blocks under this method which is called the boundary tag method.
free block allocated block
Each of the contract fields fflag, prev, size, next, bsize next and bflag is shown as occupying a complete word, although in practice they can be packed together, several fields to a word. We assume that fflag or bflag are logically flags and that true signifies an allocated block and false indicates a free block. Using the information in the free block and the newly freed block, the system merges the two blocks into a bigger hole.