tjh.dev
Linux kernel mirror (for testing)
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linux
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 * Note: The default shared memory limit is quite low on many kernels,
12 * you may need to increase it via:
13 *
14 * echo 268435456 > /proc/sys/kernel/shmmax
15 *
16 * This will increase the maximum size per shared memory segment to 256MB.
17 * The other limit that you will hit eventually is shmall which is the
18 * total amount of shared memory in pages. To set it to 16GB on a system
19 * with a 4kB pagesize do:
20 *
21 * echo 4194304 > /proc/sys/kernel/shmall
22 */
23
24#include <stdlib.h>
25#include <stdio.h>
26#include <sys/types.h>
27#include <sys/ipc.h>
28#include <sys/shm.h>
29#include <sys/mman.h>
30
31#define LENGTH (256UL*1024*1024)
32
33#define dprintf(x) printf(x)
34
35int main(void)
36{
37 int shmid;
38 unsigned long i;
39 char *shmaddr;
40
41 shmid = shmget(2, LENGTH, SHM_HUGETLB | IPC_CREAT | SHM_R | SHM_W);
42 if (shmid < 0) {
43 perror("shmget");
44 exit(1);
45 }
46 printf("shmid: 0x%x\n", shmid);
47
48 shmaddr = shmat(shmid, NULL, 0);
49 if (shmaddr == (char *)-1) {
50 perror("Shared memory attach failure");
51 shmctl(shmid, IPC_RMID, NULL);
52 exit(2);
53 }
54 printf("shmaddr: %p\n", shmaddr);
55
56 dprintf("Starting the writes:\n");
57 for (i = 0; i < LENGTH; i++) {
58 shmaddr[i] = (char)(i);
59 if (!(i % (1024 * 1024)))
60 dprintf(".");
61 }
62 dprintf("\n");
63
64 dprintf("Starting the Check...");
65 for (i = 0; i < LENGTH; i++)
66 if (shmaddr[i] != (char)i) {
67 printf("\nIndex %lu mismatched\n", i);
68 exit(3);
69 }
70 dprintf("Done.\n");
71
72 if (shmdt((const void *)shmaddr) != 0) {
73 perror("Detach failure");
74 shmctl(shmid, IPC_RMID, NULL);
75 exit(4);
76 }
77
78 shmctl(shmid, IPC_RMID, NULL);
79
80 return 0;
81}