[$] The [vx]swap showdown

The kernel's swap layer has undergone somesignificant changes over the course of the last year and a number oflongstanding problems have been addressed. One problem that has notyet been solved in the mainline is the direct tie between slots in the swapcache and space in persistent swap files, which can cause highlyinefficient resource use. There are two competing solutions for thisproblem, neither of which has, as yet, reached readiness for merging; alengthy discussion on possible paths forward shows ongoing disagreementover the best path forward.