[$] Improvements for the contiguous memory allocator

As a system runs, its memory becomes fragmented; it does not take long
before the allocation of large, physically contiguous memory ranges becomes
difficult or impossible. The contiguous memory
allocator (CMA) is a kernel subsystem that attempts to address this
problem, but it has never worked as well as some would like. Two sessions
in the memory-management track at the 2025 Linux Storage, Filesystem,
Memory-Management, and BPF Summit looked at how CMA can be improved; the
first looked at providing guaranteed allocations, while the second
addressed some inefficiencies in CMA.