Root/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
34static void check_bytes(char *addr)
35{
36    printf("First hex is %x\n", *((unsigned int *)addr));
37}
38
39static 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
47static 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
59int 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}
78

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