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-rw-r--r--Documentation/vm/hugepage-shm.c98
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diff --git a/Documentation/vm/hugepage-shm.c b/Documentation/vm/hugepage-shm.c
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-/*
- * hugepage-shm:
- *
- * Example of using huge page memory in a user application using Sys V shared
- * memory system calls. In this example the app is requesting 256MB of
- * memory that is backed by huge pages. The application uses the flag
- * SHM_HUGETLB in the shmget system call to inform the kernel that it is
- * requesting huge pages.
- *
- * For the ia64 architecture, the Linux kernel reserves Region number 4 for
- * huge pages. That means that if one requires a fixed address, a huge page
- * aligned address starting with 0x800000... will be required. If a fixed
- * address is not required, the kernel will select an address in the proper
- * range.
- * Other architectures, such as ppc64, i386 or x86_64 are not so constrained.
- *
- * Note: The default shared memory limit is quite low on many kernels,
- * you may need to increase it via:
- *
- * echo 268435456 > /proc/sys/kernel/shmmax
- *
- * This will increase the maximum size per shared memory segment to 256MB.
- * The other limit that you will hit eventually is shmall which is the
- * total amount of shared memory in pages. To set it to 16GB on a system
- * with a 4kB pagesize do:
- *
- * echo 4194304 > /proc/sys/kernel/shmall
- */
-
-#include <stdlib.h>
-#include <stdio.h>
-#include <sys/types.h>
-#include <sys/ipc.h>
-#include <sys/shm.h>
-#include <sys/mman.h>
-
-#ifndef SHM_HUGETLB
-#define SHM_HUGETLB 04000
-#endif
-
-#define LENGTH (256UL*1024*1024)
-
-#define dprintf(x) printf(x)
-
-/* Only ia64 requires this */
-#ifdef __ia64__
-#define ADDR (void *)(0x8000000000000000UL)
-#define SHMAT_FLAGS (SHM_RND)
-#else
-#define ADDR (void *)(0x0UL)
-#define SHMAT_FLAGS (0)
-#endif
-
-int main(void)
-{
- int shmid;
- unsigned long i;
- char *shmaddr;
-
- if ((shmid = shmget(2, LENGTH,
- SHM_HUGETLB | IPC_CREAT | SHM_R | SHM_W)) < 0) {
- perror("shmget");
- exit(1);
- }
- printf("shmid: 0x%x\n", shmid);
-
- shmaddr = shmat(shmid, ADDR, SHMAT_FLAGS);
- if (shmaddr == (char *)-1) {
- perror("Shared memory attach failure");
- shmctl(shmid, IPC_RMID, NULL);
- exit(2);
- }
- printf("shmaddr: %p\n", shmaddr);
-
- dprintf("Starting the writes:\n");
- for (i = 0; i < LENGTH; i++) {
- shmaddr[i] = (char)(i);
- if (!(i % (1024 * 1024)))
- dprintf(".");
- }
- dprintf("\n");
-
- dprintf("Starting the Check...");
- for (i = 0; i < LENGTH; i++)
- if (shmaddr[i] != (char)i)
- printf("\nIndex %lu mismatched\n", i);
- dprintf("Done.\n");
-
- if (shmdt((const void *)shmaddr) != 0) {
- perror("Detach failure");
- shmctl(shmid, IPC_RMID, NULL);
- exit(3);
- }
-
- shmctl(shmid, IPC_RMID, NULL);
-
- return 0;
-}