mach zero fill count

vms.c

#include <stdio.h>
#include <sys/mman.h>
#include <mach/mach.h>
#include <mach/vm_statistics.h>

void vm_stat()
{
	int host = mach_host_self();
	vm_statistics64_data_t stat;
	mach_msg_type_number_t count;
	host_statistics64(host, HOST_VM_INFO64, (host_info_t)&stat, &count);
	printf("active: %u, zero_fill: %llu\n", stat.active_count, stat.zero_fill_count);
}

int main()
{
	size_t length = 4096 * 999;
	vm_stat();
	char *p = (char *)mmap(NULL, length, PROT_WRITE | PROT_READ, MAP_ANON | MAP_PRIVATE, -1, 0);
	if (p != MAP_FAILED)
	{
		vm_stat();
		for (size_t i = 0; i < length; i += 4096) p[i] = 1;
		vm_stat();
	}
}

/*
viv@Ivans-MacBook-Pro-2 ~/none4$ clang vms.c && ./a.out && vm_stat
active: 0, zero_fill: 0
active: 779976, zero_fill: 92674893
active: 780975, zero_fill: 92675892
*/