Do you mean actual fragmentation of physical contiguous memory? Or the slowdown caused by the lengthening of the allocation table over time (because in vanilla AmigaOS it is a linked list that is traversed every single allocation)? On anything Amiga-related people constantly confuse the two.
MorphOS helped the first problem and completely removed the latter (AFAIR, anyway).https://library.morph.zone/In-depth:_The_New_MorphOS_Memory_System
And how do you even know your memory is fragmented and not simply allocated by stuff that can't be flushed?[ Edited by KennyR 04.11.2018 - 18:14 ]