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Unformatted text preview: rst ﬁt placement policy, the allocator inspects the most recently used blocks ﬁrst. In this case, freeing a block can be performed in constant time. If boundary tags are used, then coalescing can also be performed in constant time. Another approach is to maintain the list in address order, where the address of each block in the list is less than the address of its successor. In this case, freeing a block requires a linear-time search to locate the 544
31 3 21 0 31 CHAPTER 10. VIRTUAL MEMORY
3 21 0 block size a/f header block size pred (predecessor) a/f header payload succ (successor) old payload padding (optional) block size a/f footer padding (optional) block size a/f footer (a) Allocated block (b) Free block Figure 10.50: Format of heap blocks that use doubly-linked free lists. appropriate predecessor. The trade-off is that address-ordered ﬁrst ﬁt enjoys better memory utilization than LIFO-ordered ﬁrst ﬁt, approaching the utilization of best ﬁt. A disadvantage of explicit lists in general is that free...
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