[$] Flexible-order anonymous folios

The conversion to folios is intended to,among other things, make it easy for the kernel to manage chunks of memoryin a number of different sizes. So far, though, that flexibility is notbeing used in the kernel's handling of anonymous pages. At the 2023 Linux Storage, Filesystem,Memory-Management and BPF Summit, Yu Zhao and Yang Shi ran a session inthe memory-management track aimed at charting a path toward support foranonymous pages in a variety of sizes.