#include <stdio.h>
#include <sys/time.h>
#include <sys/mman.h>
#include <string.h>
#include <stdlib.h>

double mydifftime(struct timeval *tv1, struct timeval *tv2)
{
    return ((tv1->tv_sec - tv2->tv_sec) * 1000000.0 +
        (tv1->tv_usec - tv2->tv_usec)) / 1000000.0;
}

int main()
{
    int MMAP_SIZE = 1<<20;
    int i;
    printf("   size  \tmmap time\tmunmap time\tt1/t2   \tt2/size\n");

    for (i = 0; i < 11; i++, MMAP_SIZE <<= 1) {

        struct timeval tv1, tv2;
        double t1, t2;

        gettimeofday(&tv1, NULL);

        void *addr = mmap(NULL, MMAP_SIZE, PROT_READ | PROT_WRITE,
                  MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
        gettimeofday(&tv2, NULL);

        if (addr == MAP_FAILED)
            abort();
        t1 = mydifftime(&tv2, &tv1);

        /* commit memory */
        memset(addr, 1, MMAP_SIZE);

        gettimeofday(&tv1, NULL);
        munmap(addr, MMAP_SIZE);
        gettimeofday(&tv2, NULL);
        t2 = mydifftime(&tv2, &tv1);

        printf("%*d\t%f\t%f\t%f\t%f\n", 10, MMAP_SIZE, t1, t2, t2/t1,
               t2*100000000.0/(MMAP_SIZE));
    }
}