Home | History | Annotate | Download | only in vm 
      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 "huge/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 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 = open(FILE_NAME, O_CREAT | O_RDWR, 0755);
     70 	if (fd < 0) {
     71 		perror("Open failed");
     72 		exit(1);
     73 	}
     74 
     75 	addr = mmap(ADDR, LENGTH, PROTECTION, FLAGS, fd, 0);
     76 	if (addr == MAP_FAILED) {
     77 		perror("mmap");
     78 		unlink(FILE_NAME);
     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 	unlink(FILE_NAME);
     90 
     91 	return ret;
     92 }
     93