1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * hugepage-shm:
4 *
5 * Example of using huge page memory in a user application using Sys V shared
6 * memory system calls. In this example the app is requesting 256MB of
7 * memory that is backed by huge pages. The application uses the flag
8 * SHM_HUGETLB in the shmget system call to inform the kernel that it is
9 * requesting 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 * Note: The default shared memory limit is quite low on many kernels,
19 * you may need to increase it via:
20 *
21 * echo 268435456 > /proc/sys/kernel/shmmax
22 *
23 * This will increase the maximum size per shared memory segment to 256MB.
24 * The other limit that you will hit eventually is shmall which is the
25 * total amount of shared memory in pages. To set it to 16GB on a system
26 * with a 4kB pagesize do:
27 *
28 * echo 4194304 > /proc/sys/kernel/shmall
29 */
30
31 #include <stdlib.h>
32 #include <stdio.h>
33 #include <sys/types.h>
34 #include <sys/ipc.h>
35 #include <sys/shm.h>
36 #include <sys/mman.h>
37
38 #define LENGTH (256UL*1024*1024)
39
40 #define dprintf(x) printf(x)
41
42 /* Only ia64 requires this */
43 #ifdef __ia64__
44 #define ADDR (void *)(0x8000000000000000UL)
45 #define SHMAT_FLAGS (SHM_RND)
46 #else
47 #define ADDR (void *)(0x0UL)
48 #define SHMAT_FLAGS (0)
49 #endif
50
main(void)51 int main(void)
52 {
53 int shmid;
54 unsigned long i;
55 char *shmaddr;
56
57 shmid = shmget(2, LENGTH, SHM_HUGETLB | IPC_CREAT | SHM_R | SHM_W);
58 if (shmid < 0) {
59 perror("shmget");
60 exit(1);
61 }
62 printf("shmid: 0x%x\n", shmid);
63
64 shmaddr = shmat(shmid, ADDR, SHMAT_FLAGS);
65 if (shmaddr == (char *)-1) {
66 perror("Shared memory attach failure");
67 shmctl(shmid, IPC_RMID, NULL);
68 exit(2);
69 }
70 printf("shmaddr: %p\n", shmaddr);
71
72 dprintf("Starting the writes:\n");
73 for (i = 0; i < LENGTH; i++) {
74 shmaddr[i] = (char)(i);
75 if (!(i % (1024 * 1024)))
76 dprintf(".");
77 }
78 dprintf("\n");
79
80 dprintf("Starting the Check...");
81 for (i = 0; i < LENGTH; i++)
82 if (shmaddr[i] != (char)i) {
83 printf("\nIndex %lu mismatched\n", i);
84 exit(3);
85 }
86 dprintf("Done.\n");
87
88 if (shmdt((const void *)shmaddr) != 0) {
89 perror("Detach failure");
90 shmctl(shmid, IPC_RMID, NULL);
91 exit(4);
92 }
93
94 shmctl(shmid, IPC_RMID, NULL);
95
96 return 0;
97 }
98
