82 lines · c
1// SPDX-License-Identifier: GPL-2.02/*3 * hugepage-shm:4 *5 * Example of using huge page memory in a user application using Sys V shared6 * memory system calls. In this example the app is requesting 256MB of7 * memory that is backed by huge pages. The application uses the flag8 * SHM_HUGETLB in the shmget system call to inform the kernel that it is9 * requesting huge pages.10 *11 * Note: The default shared memory limit is quite low on many kernels,12 * you may need to increase it via:13 *14 * echo 268435456 > /proc/sys/kernel/shmmax15 *16 * This will increase the maximum size per shared memory segment to 256MB.17 * The other limit that you will hit eventually is shmall which is the18 * total amount of shared memory in pages. To set it to 16GB on a system19 * with a 4kB pagesize do:20 *21 * echo 4194304 > /proc/sys/kernel/shmall22 */23 24#include <stdlib.h>25#include <stdio.h>26#include <sys/types.h>27#include <sys/ipc.h>28#include <sys/shm.h>29#include <sys/mman.h>30 31#define LENGTH (256UL*1024*1024)32 33#define dprintf(x) printf(x)34 35int main(void)36{37 int shmid;38 unsigned long i;39 char *shmaddr;40 41 shmid = shmget(2, LENGTH, SHM_HUGETLB | IPC_CREAT | SHM_R | SHM_W);42 if (shmid < 0) {43 perror("shmget");44 exit(1);45 }46 printf("shmid: 0x%x\n", shmid);47 48 shmaddr = shmat(shmid, NULL, 0);49 if (shmaddr == (char *)-1) {50 perror("Shared memory attach failure");51 shmctl(shmid, IPC_RMID, NULL);52 exit(2);53 }54 printf("shmaddr: %p\n", shmaddr);55 56 dprintf("Starting the writes:\n");57 for (i = 0; i < LENGTH; i++) {58 shmaddr[i] = (char)(i);59 if (!(i % (1024 * 1024)))60 dprintf(".");61 }62 dprintf("\n");63 64 dprintf("Starting the Check...");65 for (i = 0; i < LENGTH; i++)66 if (shmaddr[i] != (char)i) {67 printf("\nIndex %lu mismatched\n", i);68 exit(3);69 }70 dprintf("Done.\n");71 72 if (shmdt((const void *)shmaddr) != 0) {73 perror("Detach failure");74 shmctl(shmid, IPC_RMID, NULL);75 exit(4);76 }77 78 shmctl(shmid, IPC_RMID, NULL);79 80 return 0;81}82