[$] Documenting page flags by committee

For every page of memory in the system, the kernel maintains a set of pageflags describing how the page is used and various aspects of its currentstate. Space for page flags has been in chronic short supply, leading to a desire toeliminate or consolidate them whenever possible. That objective, though,is hampered by the fact that the purpose of many page flags is not wellunderstood. In a memory-management-track session at the 2024 Linux Storage,Filesystem, Memory-Management and BPF Summit, Matthew Wilcox set out tocooperatively update the page-flag documentation to improve that situation.