[$] Block-layer bounce buffering bounces out of the kernel

As the end of the 1990s approached, a lot of kernel-development effort was
going into improving support for 32-bit systems
with shockingly large amounts of memory installed. This being the 1990s,
having more than 1GB of memory in such a system was deemed to be shocking.
Many of the compromises made to support such inconceivably large systems
have remained in the kernel to this day. One of those compromises —
bounce buffering of I/O requests in the block layer — has finally been
eased out for the 6.16 release, more than a quarter-century after its
introduction.