tools/testing/selftests/vm/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  * For the ia64 architecture, the Linux kernel reserves Region number 4 for
  12  * huge pages.  That means that if one requires a fixed address, a huge page
  13  * aligned address starting with 0x800000... will be required.  If a fixed
  14  * address is not required, the kernel will select an address in the proper
  15  * range.
  16  * Other architectures, such as ppc64, i386 or x86_64 are not so constrained.
  17  *
  18  * Note: The default shared memory limit is quite low on many kernels,
  19  * you may need to increase it via:
  20  *
  21  * echo 268435456 > /proc/sys/kernel/shmmax
  22  *
  23  * This will increase the maximum size per shared memory segment to 256MB.
  24  * The other limit that you will hit eventually is shmall which is the
  25  * total amount of shared memory in pages. To set it to 16GB on a system
  26  * with a 4kB pagesize do:
  27  *
  28  * echo 4194304 > /proc/sys/kernel/shmall
  29  */
  30
  31 #include <stdlib.h>
  32 #include <stdio.h>
  33 #include <sys/types.h>
  34 #include <sys/ipc.h>
  35 #include <sys/shm.h>
  36 #include <sys/mman.h>
  37
  38 #ifndef SHM_HUGETLB
  39 #define SHM_HUGETLB 04000
  40 #endif
  41
  42 #define LENGTH (256UL*1024*1024)
  43
  44 #define dprintf(x)  printf(x)
  45
  46 /* Only ia64 requires this */
  47 #ifdef __ia64__
  48 #define ADDR (void *)(0x8000000000000000UL)
  49 #define SHMAT_FLAGS (SHM_RND)
  50 #else
  51 #define ADDR (void *)(0x0UL)
  52 #define SHMAT_FLAGS (0)
  53 #endif
  54
  55 int main(void)
  56 {
  57         int shmid;
  58         unsigned long i;
  59         char *shmaddr;
  60
  61         shmid = shmget(2, LENGTH, SHM_HUGETLB | IPC_CREAT | SHM_R | SHM_W);
  62         if (shmid < 0) {
  63                 perror("shmget");
  64                 exit(1);
  65         }
  66         printf("shmid: 0x%x\n", shmid);
  67
  68         shmaddr = shmat(shmid, ADDR, SHMAT_FLAGS);
  69         if (shmaddr == (char *)-1) {
  70                 perror("Shared memory attach failure");
  71                 shmctl(shmid, IPC_RMID, NULL);
  72                 exit(2);
  73         }
  74         printf("shmaddr: %p\n", shmaddr);
  75
  76         dprintf("Starting the writes:\n");
  77         for (i = 0; i < LENGTH; i++) {
  78                 shmaddr[i] = (char)(i);
  79                 if (!(i % (1024 * 1024)))
  80                         dprintf(".");
  81         }
  82         dprintf("\n");
  83
  84         dprintf("Starting the Check...");
  85         for (i = 0; i < LENGTH; i++)
  86                 if (shmaddr[i] != (char)i) {
  87                         printf("\nIndex %lu mismatched\n", i);
  88                         exit(3);
  89                 }
  90         dprintf("Done.\n");
  91
  92         if (shmdt((const void *)shmaddr) != 0) {
  93                 perror("Detach failure");
  94                 shmctl(shmid, IPC_RMID, NULL);
  95                 exit(4);
  96         }
  97
  98         shmctl(shmid, IPC_RMID, NULL);
  99
 100         return 0;
 101 }