y/mmap_unix.go
func Madvise(b []byte, readahead bool) error {
	flags := unix.MADV_NORMAL
	if !readahead {
		flags = unix.MADV_RANDOM
	}
	return madvise(b, flags)
}
func Madvise(b []byte, readahead bool) error {
	flags := unix.MADV_NORMAL
	if !readahead {
		flags = unix.MADV_RANDOM
	}
	return madvise(b, flags)
}
// Madvise uses the madvise system call to give advise about the use of memory
// when using a slice that is memory-mapped to a file. Set the readahead flag to
// false if page references are expected in random order.