[$] Solutions for direct-map fragmentation

The kernel's 'direct map' makes the entirety of a system's physical memory
available in the kernel's virtual address space. Normally, huge pages are used for
this mapping, making it relatively efficient to access. Increasingly,
though, there is a need to carve some pages out of the direct map; this
splits up those huge pages and makes the system as a whole less efficient.
During a memory-management session at the
2022
Linux Storage, Filesystem, Memory-management and BPF Summit (LSFMM),
Mike Rapoport led a session on direct-map fragmentation and how it might be
avoided.