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

   1// SPDX-License-Identifier: GPL-2.0
   2/*
   3 * hugepage-mmap:
   4 *
   5 * Example of using huge page memory in a user application using the mmap
   6 * system call.  Before running this application, make sure that the
   7 * administrator has mounted the hugetlbfs filesystem (on some directory
   8 * like /mnt) using the command mount -t hugetlbfs nodev /mnt. In this
   9 * example, the app is requesting memory of size 256MB that is backed by
  10 * huge pages.
  11 *
  12 * For the ia64 architecture, the Linux kernel reserves Region number 4 for
  13 * huge pages.  That means that if one requires a fixed address, a huge page
  14 * aligned address starting with 0x800000... will be required.  If a fixed
  15 * address is not required, the kernel will select an address in the proper
  16 * range.
  17 * Other architectures, such as ppc64, i386 or x86_64 are not so constrained.
  18 */
  19
  20#include <stdlib.h>
  21#include <stdio.h>
  22#include <unistd.h>
  23#include <sys/mman.h>
  24#include <fcntl.h>
  25
  26#define FILE_NAME "huge/hugepagefile"
  27#define LENGTH (256UL*1024*1024)
  28#define PROTECTION (PROT_READ | PROT_WRITE)
  29
  30/* Only ia64 requires this */
  31#ifdef __ia64__
  32#define ADDR (void *)(0x8000000000000000UL)
  33#define FLAGS (MAP_SHARED | MAP_FIXED)
  34#else
  35#define ADDR (void *)(0x0UL)
  36#define FLAGS (MAP_SHARED)
  37#endif
  38
  39static void check_bytes(char *addr)
  40{
  41        printf("First hex is %x\n", *((unsigned int *)addr));
  42}
  43
  44static void write_bytes(char *addr)
  45{
  46        unsigned long i;
  47
  48        for (i = 0; i < LENGTH; i++)
  49                *(addr + i) = (char)i;
  50}
  51
  52static int read_bytes(char *addr)
  53{
  54        unsigned long i;
  55
  56        check_bytes(addr);
  57        for (i = 0; i < LENGTH; i++)
  58                if (*(addr + i) != (char)i) {
  59                        printf("Mismatch at %lu\n", i);
  60                        return 1;
  61                }
  62        return 0;
  63}
  64
  65int main(void)
  66{
  67        void *addr;
  68        int fd, ret;
  69
  70        fd = open(FILE_NAME, O_CREAT | O_RDWR, 0755);
  71        if (fd < 0) {
  72                perror("Open failed");
  73                exit(1);
  74        }
  75
  76        addr = mmap(ADDR, LENGTH, PROTECTION, FLAGS, fd, 0);
  77        if (addr == MAP_FAILED) {
  78                perror("mmap");
  79                unlink(FILE_NAME);
  80                exit(1);
  81        }
  82
  83        printf("Returned address is %p\n", addr);
  84        check_bytes(addr);
  85        write_bytes(addr);
  86        ret = read_bytes(addr);
  87
  88        munmap(addr, LENGTH);
  89        close(fd);
  90        unlink(FILE_NAME);
  91
  92        return ret;
  93}
  94