testmmap.c

#include <errno.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <time.h>
#include <stdlib.h>

#define handle_error(msg) do { perror(msg); exit(EXIT_FAILURE); } while (0);
#define OneM (1024 * 1024)

int main(int argc, char *argv[]) {
    size_t map_len = (long)25 * 1073741824; // 1024 * 1024 * 1024;
    char text_1[OneM];
    { for (int i = 0; i < OneM - 1; i ++) text_1[i] = 'w'; text_1[OneM - 1] = '\0'; }

    // Get PID
    { int pid_t = getpid(); printf("Process PID: %d\n", pid_t); }

    // dd if=/dev/random of=./f1.data bs=OneM count=65536
    int fd_1 = open("/home/ishan/work/mmap/f1.data", O_RDONLY);
    if (fd_1 < 0) { handle_error("open"); }

    char *map_region = (char *) mmap(NULL, map_len, PROT_READ, MAP_NORESERVE | MAP_PRIVATE | MAP_POPULATE, fd_1, 0);

    if(map_region == MAP_FAILED) { handle_error("Mapping Error"); }
    printf("MMap File successful: %ld bytes\n", map_len);

    srand(time(NULL));

    for (int j = 0; j < 10; j++) {
        /*
       printf("Writing file: Pass - %d\n", j);
       int wr_len = strlen(text_1);
       for (long i = 0; i < 64 * 1024; i++) {
           lseek(fd_1, i * wr_len, SEEK_SET );
           long bytesWritten = write(fd_1, text_1, wr_len);
           if (bytesWritten != strlen(text_1)) { perror("write() error"); close(fd_1); return -1; }
           else { if (i % 1024 == 0) printf("."); }
       }
       printf("\n");
         */

        printf("Reading file: Pass - %d\n", j);
        int wr_len = strlen(text_1);
        for (long i = 0; i < map_len; i++) {
            //char c = map_region[i];
            long r = rand() % map_len;
            char c = map_region[r];
            if (i % 10000000 == 0) printf("r: %llu, c: 0x%x\n", r, c & 0xff);
        }
        printf("\n");

        printf("Sleep for 5s ...\n");
        sleep(5);
    }

    printf("Sleep for 1h ...\n");
    sleep(3600);

    munmap(map_region, map_len);
    if (fd_1 > 0) { close(fd_1); }
    return 0;
}