[$] Swap tables, flash-friendly swap, swap_ops, and more

The kernel's swap subsystem is charged with managing anonymous pages insecondary storage when those pages are (hopefully) not being used and thememory they occupy is needed elsewhere. This long-unloved subsystem hasseen a resurgence of developer interest in recent times, so it is notsurprising that it was the topic of three separate sessions in thememory-management track at the2026 Linux Storage,Filesystem, Memory Management, and BPF Summit. Two of those sessionswere concerned with improving the performance and maintainability of theswap code, while one (shared with the storage track) was about how swappingcould be friendlier to solid-state storage devices.