1 // SPDX-License-Identifier: GPL-2.0
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
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
17 * Other architectures, such as ppc64, i386 or x86_64 are not so constrained.
26 #define FILE_NAME "huge/hugepagefile"
27 #define LENGTH (256UL*1024*1024)
28 #define PROTECTION (PROT_READ | PROT_WRITE)
30 /* Only ia64 requires this */
32 #define ADDR (void *)(0x8000000000000000UL)
33 #define FLAGS (MAP_SHARED | MAP_FIXED)
35 #define ADDR (void *)(0x0UL)
36 #define FLAGS (MAP_SHARED)
39 static void check_bytes(char *addr)
41 printf("First hex is %x\n", *((unsigned int *)addr));
44 static void write_bytes(char *addr)
48 for (i = 0; i < LENGTH; i++)
49 *(addr + i) = (char)i;
52 static int read_bytes(char *addr)
57 for (i = 0; i < LENGTH; i++)
58 if (*(addr + i) != (char)i) {
59 printf("Mismatch at %lu\n", i);
70 fd = open(FILE_NAME, O_CREAT | O_RDWR, 0755);
72 perror("Open failed");
76 addr = mmap(ADDR, LENGTH, PROTECTION, FLAGS, fd, 0);
77 if (addr == MAP_FAILED) {
83 printf("Returned address is %p\n", addr);
86 ret = read_bytes(addr);