1 // SPDX-License-Identifier: GPL-2.0
3 * Example of using hugepage memory in a user application using the mmap
4 * system call with MAP_HUGETLB flag. Before running this program make
5 * sure the administrator has allocated enough default sized huge pages
6 * to cover the 256 MB allocation.
8 * For ia64 architecture, Linux kernel reserves Region number 4 for hugepages.
9 * That means the addresses starting with 0x800000... will need to be
10 * specified. Specifying a fixed address is not required on ppc64, i386
19 #define LENGTH (256UL*1024*1024)
20 #define PROTECTION (PROT_READ | PROT_WRITE)
23 #define MAP_HUGETLB 0x40000 /* arch specific */
26 #ifndef MAP_HUGE_SHIFT
27 #define MAP_HUGE_SHIFT 26
31 #define MAP_HUGE_MASK 0x3f
34 /* Only ia64 requires this */
36 #define ADDR (void *)(0x8000000000000000UL)
37 #define FLAGS (MAP_PRIVATE | MAP_ANONYMOUS | MAP_HUGETLB | MAP_FIXED)
39 #define ADDR (void *)(0x0UL)
40 #define FLAGS (MAP_PRIVATE | MAP_ANONYMOUS | MAP_HUGETLB)
43 static void check_bytes(char *addr)
45 printf("First hex is %x\n", *((unsigned int *)addr));
48 static void write_bytes(char *addr, size_t length)
52 for (i = 0; i < length; i++)
53 *(addr + i) = (char)i;
56 static int read_bytes(char *addr, size_t length)
61 for (i = 0; i < length; i++)
62 if (*(addr + i) != (char)i) {
63 printf("Mismatch at %lu\n", i);
69 int main(int argc, char **argv)
73 size_t length = LENGTH;
78 length = atol(argv[1]) << 20;
80 shift = atoi(argv[2]);
82 flags |= (shift & MAP_HUGE_MASK) << MAP_HUGE_SHIFT;
86 printf("%u kB hugepages\n", 1 << (shift - 10));
88 printf("Default size hugepages\n");
89 printf("Mapping %lu Mbytes\n", (unsigned long)length >> 20);
91 addr = mmap(ADDR, length, PROTECTION, flags, -1, 0);
92 if (addr == MAP_FAILED) {
97 printf("Returned address is %p\n", addr);
99 write_bytes(addr, length);
100 ret = read_bytes(addr, length);
102 /* munmap() length of MAP_HUGETLB memory must be hugepage aligned */
103 if (munmap(addr, length)) {