[$] Dynamically allocated pseudo-filesystems

It is perhaps unusual to have a kernel tracing developer leading afilesystem session, Steven Rostedt said, at the beginning of such a session at the2022 Linux Storage,Filesystem, Memory-management and BPF Summit (LSFMM). But he was doingso totry to find a good way to dynamically allocate kernel data structuresfor some of the pseudo-filesystems, such as sysfs, debugfs, and tracefs,in the kernel.Avoiding static allocations would save memory, especially on systemsthat are not actually using any of the files in those filesystems.