shm-huge.c

#include  <sys/ipc.h>
#include  <sys/shm.h>
#include  <stdio.h>
#include  <stdlib.h>
#include <sys/mman.h>

#define MAP_HUGE_2MB    (21 << MAP_HUGE_SHIFT)

int main()
{
        int       shm_id;
        key_t     mem_key;
        int       *shm_ptr;
        int       *map;

        mem_key = ftok(".", 'a');
        /*
         * To fix ENOMEM on this one, do:
         * echo 10 > /proc/sys/vm/nr_overcommit_hugepages
         */
        shm_id = shmget(mem_key, sizeof(int), IPC_CREAT | SHM_HUGETLB | 0666);
        if (shm_id < 0) {
                perror("shmget");
                return 1;
        }

        shm_ptr = (int *) shmat(shm_id, NULL, 0);  /* attach */
        if (shm_ptr == (void *)-1) {
                perror("shmat");
                return 1;
        }

        printf("shm_ptr = %p\n", shm_ptr);

        map = mmap(NULL, sizeof(int), PROT_READ | PROT_WRITE, MAP_SHARED |
                                      MAP_ANONYMOUS, 0, 0);
        if (map == MAP_FAILED) {
                perror("mmap");
                return 1;
        }

        printf("map = %p\n", map);

        map = mmap(NULL, sizeof(int), PROT_READ | PROT_WRITE, MAP_SHARED |
                                      MAP_ANONYMOUS | MAP_HUGETLB |
                                      MAP_HUGE_2MB, 0, 0);
        if (map == MAP_FAILED) {
                perror("mmap");
                return 1;
        }

        printf("map2m = %p\n", map);
        scanf("%*s");

        return 0;
}