[$] Memory controller performance improvements

The kernel's memory controller works within the control-group mechanism toenforce memory-usage limits on groups of processes. This component hasoften had performance problems, so there is continual interest inoptimizing it. Shakeel Butt led a session during the memory-managementtrack of the 2025 Linux Storage, Filesystem, Memory-Management, and BPFSummit to look at the current state of the memory controller and what canbe done to reduce its overhead.