When you have a rapid sequence of large and small allocations, your memory starts looking like swiss cheese. To fit a large allocation you need a contiguous blo

When you have a rapid sequence of large and small allocations, your memory starts looking like swiss cheese. To fit a large allocation you need a contiguous block of free memory, but all the available blocks are too small, so it gets placed at the end where the free ram starts. Then another allocation is put right after it, the big chunk gets freed, and a small allocation is put in its place. Now instead of one big block of free memory you have a slightly smaller block, which is slightly too small to fit a large allocation, which has to be put at the end, and... I ran into this issue once debugging a performance issue with a CAD file parser. It made a lot of copies of large and small chunks, and some CAD files would cause catastrophic fragmentation. Switching out the allocator for a smarter one fixed the problem. A few versions of delphi later they put that allocator in by default, so that now it is not prone to fragmentation anymore.