1 // SPDX-License-Identifier: GPL-2.0 2 /* 3 * hugepage-mmap: 4 * 5 * Example of using huge page memory in a user application using the mmap 6 * system call. Before running this application, make sure that the 7 * administrator has mounted the hugetlbfs filesystem (on some directory 8 * like /mnt) using the command mount -t hugetlbfs nodev /mnt. In this 9 * example, the app is requesting memory of size 256MB that is backed by 10 * huge pages. 11 * 12 * For the ia64 architecture, the Linux kernel reserves Region number 4 for 13 * huge pages. That means that if one requires a fixed address, a huge page 14 * aligned address starting with 0x800000... will be required. If a fixed 15 * address is not required, the kernel will select an address in the proper 16 * range. 17 * Other architectures, such as ppc64, i386 or x86_64 are not so constrained. 18 */ 19 #define _GNU_SOURCE 20 #include <stdlib.h> 21 #include <stdio.h> 22 #include <unistd.h> 23 #include <sys/mman.h> 24 #include <fcntl.h> 25 26 #define LENGTH (256UL*1024*1024) 27 #define PROTECTION (PROT_READ | PROT_WRITE) 28 29 /* Only ia64 requires this */ 30 #ifdef __ia64__ 31 #define ADDR (void *)(0x8000000000000000UL) 32 #define FLAGS (MAP_SHARED | MAP_FIXED) 33 #else 34 #define ADDR (void *)(0x0UL) 35 #define FLAGS (MAP_SHARED) 36 #endif 37 38 static void check_bytes(char *addr) 39 { 40 printf("First hex is %x\n", *((unsigned int *)addr)); 41 } 42 43 static void write_bytes(char *addr) 44 { 45 unsigned long i; 46 47 for (i = 0; i < LENGTH; i++) 48 *(addr + i) = (char)i; 49 } 50 51 static int read_bytes(char *addr) 52 { 53 unsigned long i; 54 55 check_bytes(addr); 56 for (i = 0; i < LENGTH; i++) 57 if (*(addr + i) != (char)i) { 58 printf("Mismatch at %lu\n", i); 59 return 1; 60 } 61 return 0; 62 } 63 64 int main(void) 65 { 66 void *addr; 67 int fd, ret; 68 69 fd = memfd_create("hugepage-mmap", MFD_HUGETLB); 70 if (fd < 0) { 71 perror("memfd_create() failed"); 72 exit(1); 73 } 74 75 addr = mmap(ADDR, LENGTH, PROTECTION, FLAGS, fd, 0); 76 if (addr == MAP_FAILED) { 77 perror("mmap"); 78 close(fd); 79 exit(1); 80 } 81 82 printf("Returned address is %p\n", addr); 83 check_bytes(addr); 84 write_bytes(addr); 85 ret = read_bytes(addr); 86 87 munmap(addr, LENGTH); 88 close(fd); 89 90 return ret; 91 } 92