Function vm_page_bits_swap

freebsd/vm/vm_page.c:4951–5005

}

static inline vm_page_bits_t
vm_page_bits_swap(vm_page_t m, vm_page_bits_t *bits, vm_page_bits_t newbits)
{
#if PAGE_SIZE == 32768
	uint64_t old;

	old = *bits;
	while (atomic_fcmpset_64(bits, &old, newbits) == 0);
	return (old);
#elif PAGE_SIZE == 16384
	uint32_t old;

	old = *bits;
	while (atomic_fcmpset_32(bits, &old, newbits) == 0);
	return (old);
#elif (PAGE_SIZE == 8192) && defined(atomic_fcmpset_16)
	uint16_t old;

	old = *bits;
	while (atomic_fcmpset_16(bits, &old, newbits) == 0);
	return (old);
#elif (PAGE_SIZE == 4096) && defined(atomic_fcmpset_8)
	uint8_t old;

	old = *bits;
	while (atomic_fcmpset_8(bits, &old, newbits) == 0);
	return (old);
#else		/* PAGE_SIZE <= 4096*/
	uintptr_t addr;
	uint32_t old, new, mask;
	int shift;

	addr = (uintptr_t)bits;
	/*
	 * Use a trick to perform a 32-bit atomic on the
	 * containing aligned word, to not depend on the existence
	 * of atomic_{set, swap, clear}_{8, 16}.
	 */
	shift = addr & (sizeof(uint32_t) - 1);
#if BYTE_ORDER == BIG_ENDIAN
	shift = (sizeof(uint32_t) - sizeof(vm_page_bits_t) - shift) * NBBY;
#else
	shift *= NBBY;
#endif
	addr &= ~(sizeof(uint32_t) - 1);
	mask = VM_PAGE_BITS_ALL << shift;

	old = *bits;
	do {
		new = old & ~mask;
		new |= newbits << shift;
	} while (atomic_fcmpset_32((uint32_t *)addr, &old, new) == 0);
	return (old >> shift);
#endif		/* PAGE_SIZE */
}

/*
 *	vm_page_set_valid_range: