LXR linux/tools/testing/selftests/vm/hugepage-shm.c

   1/*
   2 * hugepage-shm:
   3 *
   4 * Example of using huge page memory in a user application using Sys V shared
   5 * memory system calls.  In this example the app is requesting 256MB of
   6 * memory that is backed by huge pages.  The application uses the flag
   7 * SHM_HUGETLB in the shmget system call to inform the kernel that it is
   8 * requesting huge pages.
   9 *
  10 * For the ia64 architecture, the Linux kernel reserves Region number 4 for
  11 * huge pages.  That means that if one requires a fixed address, a huge page
  12 * aligned address starting with 0x800000... will be required.  If a fixed
  13 * address is not required, the kernel will select an address in the proper
  14 * range.
  15 * Other architectures, such as ppc64, i386 or x86_64 are not so constrained.
  16 *
  17 * Note: The default shared memory limit is quite low on many kernels,
  18 * you may need to increase it via:
  19 *
  20 * echo 268435456 > /proc/sys/kernel/shmmax
  21 *
  22 * This will increase the maximum size per shared memory segment to 256MB.
  23 * The other limit that you will hit eventually is shmall which is the
  24 * total amount of shared memory in pages. To set it to 16GB on a system
  25 * with a 4kB pagesize do:
  26 *
  27 * echo 4194304 > /proc/sys/kernel/shmall
  28 */
  29
  30#include <stdlib.h>
  31#include <stdio.h>
  32#include <sys/types.h>
  33#include <sys/ipc.h>
  34#include <sys/shm.h>
  35#include <sys/mman.h>
  36
  37#ifndef SHM_HUGETLB
  38#define SHM_HUGETLB 04000
  39#endif
  40
  41#define LENGTH (256UL*1024*1024)
  42
  43#define dprintf(x)  printf(x)
  44
  45/* Only ia64 requires this */
  46#ifdef __ia64__
  47#define ADDR (void *)(0x8000000000000000UL)
  48#define SHMAT_FLAGS (SHM_RND)
  49#else
  50#define ADDR (void *)(0x0UL)
  51#define SHMAT_FLAGS (0)
  52#endif
  53
  54int main(void)
  55{
  56        int shmid;
  57        unsigned long i;
  58        char *shmaddr;
  59
  60        shmid = shmget(2, LENGTH, SHM_HUGETLB | IPC_CREAT | SHM_R | SHM_W);
  61        if (shmid < 0) {
  62                perror("shmget");
  63                exit(1);
  64        }
  65        printf("shmid: 0x%x\n", shmid);
  66
  67        shmaddr = shmat(shmid, ADDR, SHMAT_FLAGS);
  68        if (shmaddr == (char *)-1) {
  69                perror("Shared memory attach failure");
  70                shmctl(shmid, IPC_RMID, NULL);
  71                exit(2);
  72        }
  73        printf("shmaddr: %p\n", shmaddr);
  74
  75        dprintf("Starting the writes:\n");
  76        for (i = 0; i < LENGTH; i++) {
  77                shmaddr[i] = (char)(i);
  78                if (!(i % (1024 * 1024)))
  79                        dprintf(".");
  80        }
  81        dprintf("\n");
  82
  83        dprintf("Starting the Check...");
  84        for (i = 0; i < LENGTH; i++)
  85                if (shmaddr[i] != (char)i) {
  86                        printf("\nIndex %lu mismatched\n", i);
  87                        exit(3);
  88                }
  89        dprintf("Done.\n");
  90
  91        if (shmdt((const void *)shmaddr) != 0) {
  92                perror("Detach failure");
  93                shmctl(shmid, IPC_RMID, NULL);
  94                exit(4);
  95        }
  96
  97        shmctl(shmid, IPC_RMID, NULL);
  98
  99        return 0;
 100}
 101