H_PMD_INDEX_SIZE    6 arch/powerpc/include/asm/book3s/64/hash-4k.h #define H_PMD_INDEX_SIZE  7  // size: 8B << 7 = 1KB, maps: 2^7 x   2MB = 256MB
H_PMD_INDEX_SIZE    6 arch/powerpc/include/asm/book3s/64/hash-64k.h #define H_PMD_INDEX_SIZE  10  // size: 8B << 10 = 8KB, maps 2^10 x 16MB = 16GB