1/*
2 * hugepage-shm:
3 *
4 * Example of using huge page memory in a user application using Sys V shared
5 * memory system calls.  In this example the app is requesting 256MB of
6 * memory that is backed by huge pages.  The application uses the flag
7 * SHM_HUGETLB in the shmget system call to inform the kernel that it is
8 * requesting huge pages.
9 *
10 * For the ia64 architecture, the Linux kernel reserves Region number 4 for
11 * huge pages.  That means that if one requires a fixed address, a huge page
12 * aligned address starting with 0x800000... will be required.  If a fixed
13 * address is not required, the kernel will select an address in the proper
14 * range.
15 * Other architectures, such as ppc64, i386 or x86_64 are not so constrained.
16 *
17 * Note: The default shared memory limit is quite low on many kernels,
18 * you may need to increase it via:
19 *
20 * echo 268435456 > /proc/sys/kernel/shmmax
21 *
22 * This will increase the maximum size per shared memory segment to 256MB.
23 * The other limit that you will hit eventually is shmall which is the
24 * total amount of shared memory in pages. To set it to 16GB on a system
25 * with a 4kB pagesize do:
26 *
27 * echo 4194304 > /proc/sys/kernel/shmall
28 */
29
30#include <stdlib.h>
31#include <stdio.h>
32#include <sys/types.h>
33#include <sys/ipc.h>
34#include <sys/shm.h>
35#include <sys/mman.h>
36
37#ifndef SHM_HUGETLB
38#define SHM_HUGETLB 04000
39#endif
40
41#define LENGTH (256UL*1024*1024)
42
43#define dprintf(x)  printf(x)
44
45/* Only ia64 requires this */
46#ifdef __ia64__
47#define ADDR (void *)(0x8000000000000000UL)
48#define SHMAT_FLAGS (SHM_RND)
49#else
50#define ADDR (void *)(0x0UL)
51#define SHMAT_FLAGS (0)
52#endif
53
54int main(void)
55{
56	int shmid;
57	unsigned long i;
58	char *shmaddr;
59
60	shmid = shmget(2, LENGTH, SHM_HUGETLB | IPC_CREAT | SHM_R | SHM_W);
61	if (shmid < 0) {
62		perror("shmget");
63		exit(1);
64	}
65	printf("shmid: 0x%x\n", shmid);
66
67	shmaddr = shmat(shmid, ADDR, SHMAT_FLAGS);
68	if (shmaddr == (char *)-1) {
69		perror("Shared memory attach failure");
70		shmctl(shmid, IPC_RMID, NULL);
71		exit(2);
72	}
73	printf("shmaddr: %p\n", shmaddr);
74
75	dprintf("Starting the writes:\n");
76	for (i = 0; i < LENGTH; i++) {
77		shmaddr[i] = (char)(i);
78		if (!(i % (1024 * 1024)))
79			dprintf(".");
80	}
81	dprintf("\n");
82
83	dprintf("Starting the Check...");
84	for (i = 0; i < LENGTH; i++)
85		if (shmaddr[i] != (char)i) {
86			printf("\nIndex %lu mismatched\n", i);
87			exit(3);
88		}
89	dprintf("Done.\n");
90
91	if (shmdt((const void *)shmaddr) != 0) {
92		perror("Detach failure");
93		shmctl(shmid, IPC_RMID, NULL);
94		exit(4);
95	}
96
97	shmctl(shmid, IPC_RMID, NULL);
98
99	return 0;
100}
101