Unexpected fork failure with copy-on-write

Question

I have a program where the parent process attempts to allocate 45 GB of memory using malloc on a 4 TB server. After successful allocation, the parent forks 100 child processes. Since fork uses copy-on-write, I expected the program to run successfully without duplicating the memory.

However, the program fails to run with the error:

Failed to fork 0 (total of 0GB allocated): Cannot allocate memory

Why is this happening despite copy-on-write being used, do i need to enable any setting at the OS to enable copy on write ? Any insights are appreciated!

I was expected that total 45G will be shared with all the forked processes as processes are not doing any operation on "mem" array.

OS: RockyLinux 8.10

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>
#include <signal.h>


#define GB 45
#define FORKS 100
void main() {
    unsigned char *mem[GB];
    int i;
    for (i = 0; i < GB; i++) {
        mem[i] = malloc(1024*1024*1024);
        if (mem[i] == NULL) {
            printf("Failed to alloc %d: %s\n", i, strerror(errno));
            return;
        }
    }
    int pids[FORKS];
    for (i =0; i < FORKS; i++) {

        int pid = fork();
        if (pid == 0) {
            sleep(20);
            exit(0);
        }
        if (pid == -1) {
            printf("Failed to fork %d (total of %dGB allocated): %s\n", i, i*GB, strerror(errno));
            for (int j = 0; j < pid; j++) {
                kill(pids[j], SIGTERM);
            }
            return;
        }
        pids[i] = pid;
    }
    for (int j = 0; j < FORKS; j++) {
        kill(pids[j], SIGTERM);
    }
    printf("Success\n");
}