// SPDX-License-Identifier: GPL-2.0 /* * hugepage-mmap: * * Example of using huge page memory in a user application using the mmap * system call. Before running this application, make sure that the * administrator has mounted the hugetlbfs filesystem (on some directory * like /mnt) using the command mount -t hugetlbfs nodev /mnt. In this * example, the app is requesting memory of size 256MB that is backed by * 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. */ #include <stdlib.h> #include <stdio.h> #include <unistd.h> #include <sys/mman.h> #include <fcntl.h> #define FILE_NAME "huge/hugepagefile" #define LENGTH (256UL*1024*1024) #define PROTECTION (PROT_READ | PROT_WRITE) /* Only ia64 requires this */ #ifdef __ia64__ #define ADDR (void *)(0x8000000000000000UL) #define FLAGS (MAP_SHARED | MAP_FIXED) #else #define ADDR (void *)(0x0UL) #define FLAGS (MAP_SHARED) #endif static void check_bytes(char *addr) { printf("First hex is %x\n", *((unsigned int *)addr)); } static void write_bytes(char *addr) { unsigned long i; for (i = 0; i < LENGTH; i++) *(addr + i) = (char)i; } static int read_bytes(char *addr) { unsigned long i; check_bytes(addr); for (i = 0; i < LENGTH; i++) if (*(addr + i) != (char)i) { printf("Mismatch at %lu\n", i); return 1; } return 0; } int main(void) { void *addr; int fd, ret; fd = open(FILE_NAME, O_CREAT | O_RDWR, 0755); if (fd < 0) { perror("Open failed"); exit(1); } addr = mmap(ADDR, LENGTH, PROTECTION, FLAGS, fd, 0); if (addr == MAP_FAILED) { perror("mmap"); unlink(FILE_NAME); exit(1); } printf("Returned address is %p\n", addr); check_bytes(addr); write_bytes(addr); ret = read_bytes(addr); munmap(addr, LENGTH); close(fd); unlink(FILE_NAME); return ret; }