The Garbage Collection Handbook

Chapter 3

Mark-compact garbage collection

Fragmentation¹ can be a problem for non-moving collectors. Although there may be space available in the heap, either there may be no contiguous chunk of free space sufficiently large to handle an allocation request, or the time taken to allocate may become excessive as the memory manager has to search for suitable free space. Allocators may alleviate this problem by storing small objects of the same size together in blocks [Boehm and Weiser, 1988] especially, as we noted earlier, for applications that do not allocate many very large objects and whose ratios of different objects sizes do not change much. However, many long running applications, managed by non-moving collectors, will fragment the heap and ...