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      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 	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