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11.6. Best Fit

11.6.1. Best Fit

There is a potential disadvantage to first fit: It might “waste” larger blocks by breaking them up, and so they will not be available for large requests later. A strategy that avoids using large blocks unnecessarily is called best fit. Best fit looks at the entire list and picks the smallest block that is at least as large as the request (i.e., the “best” or closest fit to the request). Continuing with the preceding example, the best fit for a request of 30 units is the block of size 32, leaving a remainder of size 2. Best fit has the disadvantage that it requires that the entire list be searched. Another problem is that the remaining portion of the best-fit block is likely to be small, and thus useless for future requests. In other words, best fit tends to maximize problems of external fragmentation while it minimizes the chance of not being able to service an occasional large request.

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