COW testcase for Huge pages

cow-huge.c

/*                                                                              
 ============================================================================
 Name        : cow-huge.c
 Author      : hev <r@hev.cc>
 Copyright   : Copyright (c) 2022 hev
 Description : COW testcase for Huge pages
 ============================================================================
 */

#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <sys/mman.h>
#include <sys/wait.h>

static inline void
pagefill (void *ptr, size_t size, int val)
{
    unsigned long i;

    for (i = 0; i < size; i += 4096)
        *(volatile int *)(ptr + i) = val;
}

static inline unsigned long
checksum (void *ptr, size_t size)
{
    unsigned long sum = 0;
    unsigned long i;

    for (i = 0; i < size; i += sizeof(unsigned long))
        sum += *(volatile unsigned long *)(ptr + i);

    return sum;
}

int
main (int argc, char *argv[])
{
    const size_t memsize = 32 * 1024 * 1024UL;
    pid_t pid;
    void *ptr;

    ptr = mmap (NULL, memsize, PROT_READ | PROT_WRITE,
                MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
    if (ptr == MAP_FAILED) {
        return -1;
    }

    for (;;) {
        pagefill (ptr, memsize, 0);

        pid = fork ();
        switch (pid) {
        case -1:
            return -2;
        case 0:
            printf ("c sum: %lu\n", checksum (ptr, memsize));
            return 0;
        default:
            pagefill (ptr, memsize, 1);
            waitpid (pid, NULL, 0);
            printf ("p sum: %lu\n", checksum (ptr, memsize));
        }
    }

    return 0;
}