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
  39 static void check_bytes(char *addr)
  40 {
  41         printf("First hex is %x\n", *((unsigned int *)addr));
  42 }
  43
  44 static 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
  52 static 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
  65 int 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 }