[$] Three ways to rework the swap subsystem

The kernel's swap subsystem is complex and highly optimized — though not
always optimized for today's workloads. In three adjacent sessions during
the memory-management track of the 2025 Linux Storage, Filesystem,
Memory-Management, and BPF Summit, Kairui Song, Nhat Pham, and Usama Arif
all talked about some of the problems that they are trying to solve in the
Linux swap subsystem. In the first two cases, the solutions take the form of
an additional layer of indirection in the kernel's swap map; the third,
which enables swap-in of large folios, may or may not be worthwhile in the
end.