pagefaults.c

#include <stdlib.h>
#include <stdio.h>
#include <err.h>
#include <sys/mman.h>

#define DEFAULT_SIZE        (40 * 1024 * 1024)
#define PG_SIZE     4096

void failcheck(int ret, const char* what) {
    if (ret) {
        err(EXIT_FAILURE, "%s failed", what);
    } else {
        printf("%s OK\n", what);
    }
}

int main(int argc, char **argv) {
    size_t size = (argc == 2 ? atol(argv[1]) : DEFAULT_SIZE);
    char *mem;
    if (getenv("DO_MMAP")) {
        int flags = MAP_PRIVATE | MAP_ANONYMOUS | (getenv("DO_POPULATE") ? MAP_POPULATE : 0);
        mem = mmap(0, size, PROT_READ | PROT_WRITE, flags, -1, 0);
        failcheck(mem == MAP_FAILED, "mmap");
    } else {
        mem = malloc(size);
    }
    if (getenv("DO_THP")) {
        failcheck(madvise(mem, size, MADV_HUGEPAGE), "madvise");
    }

    if (getenv("DO_MADVISE")) {
        failcheck(madvise(mem, size, MADV_WILLNEED), "madvise");
    }

    if (getenv("DO_MLOCK")) {
        failcheck(mlock(mem, size), "mlock");
        failcheck(munlock(mem, size), "munlock");
    }

    for (volatile char *p = mem; p < mem + size; p += PG_SIZE) {
        *p = 'z';
    }
    
    printf("size: %6.2f MiB, pages touched: %zu\npoitner value : %p\n",
            size / 1024. / 1024., size / PG_SIZE, mem);
}