> you just need to make sure that the system keeps a big enough buffer of contiguous-enough space somewhere. Similar to how many filesystems allow you to reserve space for root
Said file system reserving can fill up (I've experienced that :) ). Could perhaps engineer some super-equation for a global reserved memory size that can actually guarantee being sufficient; but, unless you mark allocations as needing reserved space vs not and compute based on that (which is back to overhead), that'll necessarily waste a good amount of memory.
And such a global equation of course can result in global failure if just one subsystem miscalculates its required reserved amount, or the calculations improperly account for worst-case non-contiguousness or interleaved different-size-linked-list-alloc-requests or whatever. (never mind that you now need to alloc when adding elements to linked lists, an action that would otherwise be 1-4 inlined stores)
Probably (?) possible to handle, but way way way more easy to break or get wrong (with very-difficult-to-debug consequences) than just some pointer fields.
Oh and also of course, if you store list data in a separate allocation from the main object, you lose the ability to do O(1) (and extremely-cheap at that) "remove self from linked list just given my own pointer", which is probably quite common (and you can't even O(1) with an arraylist instead of a linkedlist).
Said file system reserving can fill up (I've experienced that :) ). Could perhaps engineer some super-equation for a global reserved memory size that can actually guarantee being sufficient; but, unless you mark allocations as needing reserved space vs not and compute based on that (which is back to overhead), that'll necessarily waste a good amount of memory.
And such a global equation of course can result in global failure if just one subsystem miscalculates its required reserved amount, or the calculations improperly account for worst-case non-contiguousness or interleaved different-size-linked-list-alloc-requests or whatever. (never mind that you now need to alloc when adding elements to linked lists, an action that would otherwise be 1-4 inlined stores)
Probably (?) possible to handle, but way way way more easy to break or get wrong (with very-difficult-to-debug consequences) than just some pointer fields.
Oh and also of course, if you store list data in a separate allocation from the main object, you lose the ability to do O(1) (and extremely-cheap at that) "remove self from linked list just given my own pointer", which is probably quite common (and you can't even O(1) with an arraylist instead of a linkedlist).