Since the 2.0 kernel release, Linux has supported a large number of SMP systems based on a variety of CPUs. Linux has done an excellent job of abstracting differences among these CPUs, even in kernel code. This article is an overview of one important difference: how CPUs allow memory accesses to be reordered in SMP systems.

Part 2 really gets into it: https://www.linuxjournal.com/article/8212

Also: https://www.cs.utexas.edu/~bornholt/post/memory-models.html