Documentation/vm/hugepage-mmap.c

   1 /*
   2  * hugepage-mmap:
   3  *
   4  * Example of using huge page memory in a user application using the mmap
   5  * system call.  Before running this application, make sure that the
   6  * administrator has mounted the hugetlbfs filesystem (on some directory
   7  * like /mnt) using the command mount -t hugetlbfs nodev /mnt. In this
   8  * example, the app is requesting memory of size 256MB that is backed by
   9  * 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
  19 #include <stdlib.h>
  20 #include <stdio.h>
  21 #include <unistd.h>
  22 #include <sys/mman.h>
  23 #include <fcntl.h>
  24
  25 #define FILE_NAME "/mnt/hugepagefile"
  26 #define LENGTH (256UL*1024*1024)
  27 #define PROTECTION (PROT_READ | PROT_WRITE)
  28
  29 /* Only ia64 requires this */
  30 #ifdef __ia64__
  31 #define ADDR (void *)(0x8000000000000000UL)
  32 #define FLAGS (MAP_SHARED | MAP_FIXED)
  33 #else
  34 #define ADDR (void *)(0x0UL)
  35 #define FLAGS (MAP_SHARED)
  36 #endif
  37
  38 static void check_bytes(char *addr)
  39 {
  40         printf("First hex is %x\n", *((unsigned int *)addr));
  41 }
  42
  43 static void write_bytes(char *addr)
  44 {
  45         unsigned long i;
  46
  47         for (i = 0; i < LENGTH; i++)
  48                 *(addr + i) = (char)i;
  49 }
  50
  51 static void read_bytes(char *addr)
  52 {
  53         unsigned long i;
  54
  55         check_bytes(addr);
  56         for (i = 0; i < LENGTH; i++)
  57                 if (*(addr + i) != (char)i) {
  58                         printf("Mismatch at %lu\n", i);
  59                         break;
  60                 }
  61 }
  62
  63 int main(void)
  64 {
  65         void *addr;
  66         int fd;
  67
  68         fd = open(FILE_NAME, O_CREAT | O_RDWR, 0755);
  69         if (fd < 0) {
  70                 perror("Open failed");
  71                 exit(1);
  72         }
  73
  74         addr = mmap(ADDR, LENGTH, PROTECTION, FLAGS, fd, 0);
  75         if (addr == MAP_FAILED) {
  76                 perror("mmap");
  77                 unlink(FILE_NAME);
  78                 exit(1);
  79         }
  80
  81         printf("Returned address is %p\n", addr);
  82         check_bytes(addr);
  83         write_bytes(addr);
  84         read_bytes(addr);
  85
  86         munmap(addr, LENGTH);
  87         close(fd);
  88         unlink(FILE_NAME);
  89
  90         return 0;
  91 }