[aidenn0]

> But why not? Couldn't we store information about old pointers somewhere and match them with new addresses when defragmenting? Some kind of virtual memory driver that would map old pointers to new adresses transparently for the programs? Or would it be too much overhead for too little benefit?

In languages where memory is managed for you, you can absolutely do this, since the runtime can find every single pointer to an object and rewrite it.

Virtual memory can let you do this, but would require a separate page for each allocation (since virtual memory operates on a page-level). Given that the smallest page on modern architectures is 4k, this would mean using 4k of ram for each allocation (and rounding up each allocation to a 4k page boundary).

On top of that, it's an OS system call to map and unmap pages, which means you incur a system-call on every allocation and deallocation, which is much slower than using a user-space allocator.