allocate memory to test system behavior

alloc-mem-test.cpp

#include <stdio.h>
#include <stdlib.h>

// malloc some number of gigabytes, to test impact on system
// g++ -O3 alloc-mem-test.cpp && ./a.out

size_t WIDTH = 75;
int progress_bar(size_t i, size_t size) {
    return i * WIDTH / size;
}

int main(int argc, char *argv[]) {
    if (argc < 2) {
        fprintf(stderr, "argument expected, size in Gb\n");
        return 1;
    }
    size_t size_gb = atoi(argv[1]);
    if (size_gb == 0) {
        fprintf(stderr, "invalid size\n");
        return 1;
    }
    size_t size = size_gb * 1024 * 1024 * 1024;
    char *p = (char*)malloc(size);
    if (!p) {
        fprintf(stderr, "malloc returns null\n");
        return 1;
    }

    printf("[");
    for (int i = 0; i < WIDTH-2; ++i)
        printf("-");
    printf("]\n");

    int npass = 100;
    for (int pass = 0; pass < npass; ++pass) {
        printf("pass %d/%d\n", pass+1, npass);
        const size_t page_size = 4096;
        for (size_t i = 0; i < size; i += page_size) {
            p[i] = 0;
            if (progress_bar(i - page_size, size)  != progress_bar(i, size)) {
                printf(".");
                fflush(stdout);
            }
        }
        printf("\n");
    }


    return 0;
}