[$] Per-CPU memory for user space

The kernel makes extensive use of per-CPU data as a way to avoid contention
between processors and improve scalability. Using the same technique in
user space is harder, though, since there is little control over which CPU
a process may be running on at any given time. That hasn't stopped Mathieu
Desnoyers from trying, though; in the memory-management track of the 2025
Linux Storage, Filesystem, Memory-Management, and BPF Summit, he presented
a proposal for how user-space per-CPU memory could work.