| 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 | |
| 54 | int main(void) |
| 55 | { |
| 56 | int shmid; |
| 57 | unsigned long i; |
| 58 | char *shmaddr; |
| 59 | |
| 60 | if ((shmid = shmget(2, LENGTH, |
| 61 | SHM_HUGETLB | IPC_CREAT | SHM_R | SHM_W)) < 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 | dprintf("Done.\n"); |
| 88 | |
| 89 | if (shmdt((const void *)shmaddr) != 0) { |
| 90 | perror("Detach failure"); |
| 91 | shmctl(shmid, IPC_RMID, NULL); |
| 92 | exit(3); |
| 93 | } |
| 94 | |
| 95 | shmctl(shmid, IPC_RMID, NULL); |
| 96 | |
| 97 | return 0; |
| 98 | } |