// SPDX-License-Identifier: GPL-2.0
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/*
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* hugepage-shm:
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*
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* Example of using huge page memory in a user application using Sys V shared
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* memory system calls. In this example the app is requesting 256MB of
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* memory that is backed by huge pages. The application uses the flag
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* SHM_HUGETLB in the shmget system call to inform the kernel that it is
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* requesting huge pages.
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*
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* For the ia64 architecture, the Linux kernel reserves Region number 4 for
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* huge pages. That means that if one requires a fixed address, a huge page
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* aligned address starting with 0x800000... will be required. If a fixed
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* address is not required, the kernel will select an address in the proper
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* range.
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* Other architectures, such as ppc64, i386 or x86_64 are not so constrained.
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*
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* Note: The default shared memory limit is quite low on many kernels,
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* you may need to increase it via:
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*
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* echo 268435456 > /proc/sys/kernel/shmmax
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*
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* This will increase the maximum size per shared memory segment to 256MB.
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* The other limit that you will hit eventually is shmall which is the
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* total amount of shared memory in pages. To set it to 16GB on a system
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* with a 4kB pagesize do:
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*
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* echo 4194304 > /proc/sys/kernel/shmall
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*/
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#include <stdlib.h>
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#include <stdio.h>
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#include <sys/types.h>
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#include <sys/ipc.h>
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#include <sys/shm.h>
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#include <sys/mman.h>
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#ifndef SHM_HUGETLB
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#define SHM_HUGETLB 04000
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#endif
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#define LENGTH (256UL*1024*1024)
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#define dprintf(x) printf(x)
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/* Only ia64 requires this */
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#ifdef __ia64__
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#define ADDR (void *)(0x8000000000000000UL)
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#define SHMAT_FLAGS (SHM_RND)
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#else
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#define ADDR (void *)(0x0UL)
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#define SHMAT_FLAGS (0)
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#endif
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int main(void)
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{
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int shmid;
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unsigned long i;
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char *shmaddr;
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shmid = shmget(2, LENGTH, SHM_HUGETLB | IPC_CREAT | SHM_R | SHM_W);
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if (shmid < 0) {
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perror("shmget");
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exit(1);
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}
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printf("shmid: 0x%x\n", shmid);
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shmaddr = shmat(shmid, ADDR, SHMAT_FLAGS);
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if (shmaddr == (char *)-1) {
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perror("Shared memory attach failure");
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shmctl(shmid, IPC_RMID, NULL);
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exit(2);
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}
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printf("shmaddr: %p\n", shmaddr);
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dprintf("Starting the writes:\n");
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for (i = 0; i < LENGTH; i++) {
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shmaddr[i] = (char)(i);
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if (!(i % (1024 * 1024)))
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dprintf(".");
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}
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dprintf("\n");
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dprintf("Starting the Check...");
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for (i = 0; i < LENGTH; i++)
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if (shmaddr[i] != (char)i) {
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printf("\nIndex %lu mismatched\n", i);
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exit(3);
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}
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dprintf("Done.\n");
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if (shmdt((const void *)shmaddr) != 0) {
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perror("Detach failure");
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shmctl(shmid, IPC_RMID, NULL);
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exit(4);
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}
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shmctl(shmid, IPC_RMID, NULL);
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return 0;
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}
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