LXR linux/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
  55int 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}
 102