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 #define _GNU_SOURCE
20 #include <stdlib.h>
21 #include <stdio.h>
22 #include <unistd.h>
23 #include <sys/mman.h>
24 #include <fcntl.h>
25
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
check_bytes(char * addr)38 static void check_bytes(char *addr)
39 {
40 printf("First hex is %x\n", *((unsigned int *)addr));
41 }
42
write_bytes(char * addr)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
read_bytes(char * addr)51 static int 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 return 1;
60 }
61 return 0;
62 }
63
main(void)64 int main(void)
65 {
66 void *addr;
67 int fd, ret;
68
69 fd = memfd_create("hugepage-mmap", MFD_HUGETLB);
70 if (fd < 0) {
71 perror("memfd_create() failed");
72 exit(1);
73 }
74
75 addr = mmap(ADDR, LENGTH, PROTECTION, FLAGS, fd, 0);
76 if (addr == MAP_FAILED) {
77 perror("mmap");
78 close(fd);
79 exit(1);
80 }
81
82 printf("Returned address is %p\n", addr);
83 check_bytes(addr);
84 write_bytes(addr);
85 ret = read_bytes(addr);
86
87 munmap(addr, LENGTH);
88 close(fd);
89
90 return ret;
91 }
92
