[$] Large-folio support for shmem and tmpfs

The kernel contains a pair of related filesystems that, among other things,can be used for shared-memory applications; shmem is an internal mechanismused within the kernel, while the tmpfs filesystem is mounted andaccessible from user space. As is the case elsewhere in the kernel, thesesubsystems would benefit from the addition of large-folio support. Duringa joint storage, filesystem, and memory-management session at the 2024 Linux Storage,Filesystem, Memory-Management and BPF Summit, Daniel Gomez talked aboutthe work he is doing to add that support.