FAQ 33.05 How else can member objects improve performance over pointers?

By reducing the number of freestore allocations and the fragmentation of memory.

In a CPU-bound application, freestore operations are generally very slow primitives: the more objects that are allocated from the freestore, the worse the performance. By moving the member object physically inside the outer object, as shown in d_ in FAQ 33.04, there are fewer freestore operations.

In addition, memory can become fragmented when the freestore is used excessively. For example, an entire page of memory may need to be brought into RAM just because a small piece is being used, even though 99% of the page is not being used. If this happens frequently, it can lead to thrashing, which can significantly degrade performance. By moving the member object physically inside the outer object, as shown in FAQ 33.04 the memory is less fragmented.

In some extreme performance-sensitive applications, cache misses can be a significant problem. In these cases, data structures must be carefully laid out to minimize the number of cache lines that need to be brought into the CPU, which again means minimizing fragmentation.