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      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 #ifndef SHM_HUGETLB
     39 #define SHM_HUGETLB 04000
     40 #endif
     41 
     42 #define LENGTH (256UL*1024*1024)
     43 
     44 #define dprintf(x)  printf(x)
     45 
     46 /* Only ia64 requires this */
     47 #ifdef __ia64__
     48 #define ADDR (void *)(0x8000000000000000UL)
     49 #define SHMAT_FLAGS (SHM_RND)
     50 #else
     51 #define ADDR (void *)(0x0UL)
     52 #define SHMAT_FLAGS (0)
     53 #endif
     54 
     55 int main(void)
     56 {
     57 	int shmid;
     58 	unsigned long i;
     59 	char *shmaddr;
     60 
     61 	shmid = shmget(2, LENGTH, SHM_HUGETLB | IPC_CREAT | SHM_R | SHM_W);
     62 	if (shmid < 0) {
     63 		perror("shmget");
     64 		exit(1);
     65 	}
     66 	printf("shmid: 0x%x\n", shmid);
     67 
     68 	shmaddr = shmat(shmid, ADDR, SHMAT_FLAGS);
     69 	if (shmaddr == (char *)-1) {
     70 		perror("Shared memory attach failure");
     71 		shmctl(shmid, IPC_RMID, NULL);
     72 		exit(2);
     73 	}
     74 	printf("shmaddr: %p\n", shmaddr);
     75 
     76 	dprintf("Starting the writes:\n");
     77 	for (i = 0; i < LENGTH; i++) {
     78 		shmaddr[i] = (char)(i);
     79 		if (!(i % (1024 * 1024)))
     80 			dprintf(".");
     81 	}
     82 	dprintf("\n");
     83 
     84 	dprintf("Starting the Check...");
     85 	for (i = 0; i < LENGTH; i++)
     86 		if (shmaddr[i] != (char)i) {
     87 			printf("\nIndex %lu mismatched\n", i);
     88 			exit(3);
     89 		}
     90 	dprintf("Done.\n");
     91 
     92 	if (shmdt((const void *)shmaddr) != 0) {
     93 		perror("Detach failure");
     94 		shmctl(shmid, IPC_RMID, NULL);
     95 		exit(4);
     96 	}
     97 
     98 	shmctl(shmid, IPC_RMID, NULL);
     99 
    100 	return 0;
    101 }
    102