Based on kernel version 3.3. Page generated on 2012-03-23 21:41 EST.
1 /* 2 * hugepage-mmap: 3 * 4 * Example of using huge page memory in a user application using the mmap 5 * system call. Before running this application, make sure that the 6 * administrator has mounted the hugetlbfs filesystem (on some directory 7 * like /mnt) using the command mount -t hugetlbfs nodev /mnt. In this 8 * example, the app is requesting memory of size 256MB that is backed by 9 * 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 19 #include <stdlib.h> 20 #include <stdio.h> 21 #include <unistd.h> 22 #include <sys/mman.h> 23 #include <fcntl.h> 24 25 #define FILE_NAME "/mnt/hugepagefile" 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 void 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 break; 60 } 61 } 62 63 int main(void) 64 { 65 void *addr; 66 int fd; 67 68 fd = open(FILE_NAME, O_CREAT | O_RDWR, 0755); 69 if (fd < 0) { 70 perror("Open failed"); 71 exit(1); 72 } 73 74 addr = mmap(ADDR, LENGTH, PROTECTION, FLAGS, fd, 0); 75 if (addr == MAP_FAILED) { 76 perror("mmap"); 77 unlink(FILE_NAME); 78 exit(1); 79 } 80 81 printf("Returned address is %p\n", addr); 82 check_bytes(addr); 83 write_bytes(addr); 84 read_bytes(addr); 85 86 munmap(addr, LENGTH); 87 close(fd); 88 unlink(FILE_NAME); 89 90 return 0; 91 }