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 
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