Wakelocks and allocation of physically contiguous memory allocations (ashmem, dumped now in favor of dmabuff). All upstreamed now.
At this point, Androids kernel is only a fork of upstream Linux kernel because Google employs so many kernel devs that some features are developed downstream first, then upstreamed once kinks are worked out after shipping in devices on tighter deadlines than upstream.
> allocation of physically contiguous memory allocations (ashmem, dumped now in favor of dmabuff).
ashmem is user space shared memory with permission controls. It was replaced(ish) with memfd with the addition of F_SEAL_FUTURE_WRITE in 5.1 (it took a shockingly long time for that to finally have feature parity but hey better late than never)
ION is the special allocator that was replaced with dmabuf.
Also ARM, qcom, etc... all love playing with the scheduler or making other changes which typically happens downstream first for time-to-market reasons before being upstreamed. eg, ARM's EAS / energy aware scheduling I think actually shipped to users prior to upstream accepting it.
Did the maintainer change on linux side to make linux more comfortable with the stuff coming from android? It felt like back in the days there was a real resistance on the linux side - even though the linux "solutions" where more theoretical.
At this point, Androids kernel is only a fork of upstream Linux kernel because Google employs so many kernel devs that some features are developed downstream first, then upstreamed once kinks are worked out after shipping in devices on tighter deadlines than upstream.