On Sun, Nov 01, 2020 at 07:04:50PM +0200, Mike Rapoport wrote:

From: Mike Rapoport <redacted>

ARM and ARM64 free unused parts of the memory map just before the
initialization of the page allocator. To allow holes in the memory map both
architectures overload pfn_valid() and define HAVE_ARCH_PFN_VALID.

Allowing holes in the memory map for FLATMEM may be useful for small
machines, such as ARC and m68k and will enable those architectures to cease
using DISCONTIGMEM and still support more than one memory bank.

Move the functions that free unused memory map to generic mm and enable
them in case HAVE_ARCH_PFN_VALID=y.

Signed-off-by: Mike Rapoport <redacted>

For arm64:

Acked-by: Catalin Marinas <catalin.marinas@arm.com>