worstfit

Worst-fit is a memory allocation strategy used in dynamic memory allocation and operating system memory management. It works by selecting the largest available free block that can satisfy a given memory request, rather than the first suitable block or the one that most closely matches the request.

In operation, a system maintains a free list of unallocated memory blocks. To allocate a size s, the allocator identifies the largest free block with size at least s. If no such block exists, the allocation fails. If the largest block exactly equals s, it is removed from the free list and returned to the requester. If the block is larger than s, it is split: the requested portion is allocated, and the residual portion (size equal to the block size minus s) remains as a free block.

Deallocation returns memory to the free list and may merge the freed block with adjacent free blocks to reduce fragmentation. The effectiveness of worst-fit depends on how coalescing is implemented and how the free blocks are organized.

Advantages and disadvantages are debated. Worst-fit can help preserve large blocks for potential future allocations, but it often leads to higher external fragmentation and slower allocations, since the allocator must search for the largest block and frequently creates many small free blocks. In practice, worst-fit is less commonly used than first-fit or best-fit in general-purpose allocators, though it may be chosen in specific workloads or educational demonstrations to illustrate fragmentation behavior.

Implementation considerations include data structures for maintaining free blocks (such as lists, trees, or heaps) and the impact of coalescing policies on fragmentation and performance.