[$] Faster page faults with RCU-protected VMA walks

Looking up a virtual memory area (VMA) in a process's address space, forthe handling of page faults or any of a number of other tasks, inmulti-threaded processes has long been bedeviled by lock contention in thekernel. As a result, developer gatherings have been subjected to manysessions on how to improve the situation. At the 2024 Linux Storage,Filesystem, Memory-Management and BPF Summit, developers in thememory-management track met, in a session led by Liam Howlett, to talkabout a situation that has improved considerably in recent times, but whichstill offers opportunities for optimization.