tools/testing/selftests/mm/hugepage-shm.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * hugepage-shm:
   4  *
   5  * Example of using huge page memory in a user application using Sys V shared
   6  * memory system calls.  In this example the app is requesting 256MB of
   7  * memory that is backed by huge pages.  The application uses the flag
   8  * SHM_HUGETLB in the shmget system call to inform the kernel that it is
   9  * 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/shmmax
  15  *
  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 the
  18  * total amount of shared memory in pages. To set it to 16GB on a system
  19  * with a 4kB pagesize do:
  20  *
  21  * echo 4194304 > /proc/sys/kernel/shmall
  22  */
  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
  35 int 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 }