PAGE_SHIFT、PAGE_SIZE、PAGE_MASK
#define PAGE_SHIFT 12
define PAGE_SIZE (1UL << PAGE_SHIFT)
#define PAGE_MASK (~(PAGE_SIZE-1))
PAGE_SHIFT = 12
PAGE_SIZE = 1<<12=2^12
PAGE_MASK = 0000 0000 0000
说明:
1 << N : 就是第N+1位为1
2^N-1 : 就是N个位为1
PMD_SHIFT、PMD_SIZE、PMDMASK
#define PMD_SHIFT PUD_SHIFT
#define PTRS_PER_PMD 1
#define PMD_SIZE (1UL << PMD_SHIFT)
#define PMD_MASK (~(PMD_SIZE-1))
PMD_SHIFT = 22
PMD_SIZE = 1 << 22= 2^22
PMD_MASK = 0000 0000 0000 0000 0000 00