Documentation/vm/map_hugetlb.c

   1 /*
   2  * Example of using hugepage memory in a user application using the mmap
   3  * system call with MAP_HUGETLB flag.  Before running this program make
   4  * sure the administrator has allocated enough default sized huge pages
   5  * to cover the 256 MB allocation.
   6  *
   7  * For ia64 architecture, Linux kernel reserves Region number 4 for hugepages.
   8  * That means the addresses starting with 0x800000... will need to be
   9  * specified.  Specifying a fixed address is not required on ppc64, i386
  10  * or x86_64.
  11  */
  12 #include <stdlib.h>
  13 #include <stdio.h>
  14 #include <unistd.h>
  15 #include <sys/mman.h>
  16 #include <fcntl.h>
  17
  18 #define LENGTH (256UL*1024*1024)
  19 #define PROTECTION (PROT_READ | PROT_WRITE)
  20
  21 #ifndef MAP_HUGETLB
  22 #define MAP_HUGETLB 0x40000 /* arch specific */
  23 #endif
  24
  25 /* Only ia64 requires this */
  26 #ifdef __ia64__
  27 #define ADDR (void *)(0x8000000000000000UL)
  28 #define FLAGS (MAP_PRIVATE | MAP_ANONYMOUS | MAP_HUGETLB | MAP_FIXED)
  29 #else
  30 #define ADDR (void *)(0x0UL)
  31 #define FLAGS (MAP_PRIVATE | MAP_ANONYMOUS | MAP_HUGETLB)
  32 #endif
  33
  34 static void check_bytes(char *addr)
  35 {
  36         printf("First hex is %x\n", *((unsigned int *)addr));
  37 }
  38
  39 static void write_bytes(char *addr)
  40 {
  41         unsigned long i;
  42
  43         for (i = 0; i < LENGTH; i++)
  44                 *(addr + i) = (char)i;
  45 }
  46
  47 static void read_bytes(char *addr)
  48 {
  49         unsigned long i;
  50
  51         check_bytes(addr);
  52         for (i = 0; i < LENGTH; i++)
  53                 if (*(addr + i) != (char)i) {
  54                         printf("Mismatch at %lu\n", i);
  55                         break;
  56                 }
  57 }
  58
  59 int main(void)
  60 {
  61         void *addr;
  62
  63         addr = mmap(ADDR, LENGTH, PROTECTION, FLAGS, 0, 0);
  64         if (addr == MAP_FAILED) {
  65                 perror("mmap");
  66                 exit(1);
  67         }
  68
  69         printf("Returned address is %p\n", addr);
  70         check_bytes(addr);
  71         write_bytes(addr);
  72         read_bytes(addr);
  73
  74         munmap(addr, LENGTH);
  75
  76         return 0;
  77 }