Root/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
38static void check_bytes(char *addr)
39{
40    printf("First hex is %x\n", *((unsigned int *)addr));
41}
42
43static 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
51static 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
63int 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}
92

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