system call or standard SYSv shared memory system calls (shmget, shmat).
*******************************************************************
/*
* Example of using hugepage memory in a user application using Sys V shared
* memory system calls. In this example the app is requesting 256MB of
* memory that is backed by huge pages. The application uses the flag
* SHM_HUGETLB in the shmget system call to inform the kernel that it is
* requesting hugepages.
*
* For the ia64 architecture, the Linux kernel reserves Region number 4 for
* hugepages. That means the addresses starting with 0x800000... will need
* to be specified. Specifying a fixed address is not required on ppc64,
* i386 or x86_64.
*
* Note: The default shared memory limit is quite low on many kernels,
* you may need to increase it via:
*
* echo 268435456 > /proc/sys/kernel/shmmax
*
* This will increase the maximum size per shared memory segment to 256MB.
* The other limit that you will hit eventually is shmall which is the
* total amount of shared memory in pages. To set it to 16GB on a system
* with a 4kB pagesize do:
*
* echo 4194304 > /proc/sys/kernel/shmall
*/
#include
#include
#include
#include
#include
#include
#ifndef SHM_HUGETLB
#define SHM_HUGETLB 04000
#endif
#define LENGTH (256UL*1024*1024)
#define dprintf(x) printf(x)
/* Only ia64 requires this */
#ifdef __ia64__
#define ADDR (void *)(0x8000000000000000UL)
#define SHMAT_FLAGS (SHM_RND)
#else
#define ADDR (void *)(0x0UL)
#define SHMAT_FLAGS (0)
#endif
int main(void)
{
int shmid;
unsigned long i;
char *shmaddr;
if ((shmid = shmget(2, LENGTH,
SHM_HUGETLB | IPC_CREAT | SHM_R | SHM_W)) < 0) {
perror("shmget");
exit(1);
}
printf("shmid: 0x%x\n", shmid);
shmaddr = shmat(shmid, ADDR, SHMAT_FLAGS);
if (shmaddr == (char *)-1) {
perror("Shared memory attach failure");
shmctl(shmid, IPC_RMID, NULL);
exit(2);
}
printf("shmaddr: %p\n", shmaddr);
dprintf("Starting the writes:\n");
for (i = 0; i < LENGTH; i++) {
shmaddr[i] = (char)(i);
if (!(i % (1024 * 1024)))
dprintf(".");
}
dprintf("\n");
dprintf("Starting the Check...");
for (i = 0; i < LENGTH; i++)
if (shmaddr[i] != (char)i)
printf("\nIndex %lu mismatched\n", i);
dprintf("Done.\n");
if (shmdt((const void *)shmaddr) != 0) {
perror("Detach failure");
shmctl(shmid, IPC_RMID, NULL);
exit(3);
}
shmctl(shmid, IPC_RMID, NULL);
return 0;
}
*******************************************************************
/*
* Example of using hugepage 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 ia64 architecture, Linux kernel reserves Region number 4 for hugepages.
* That means the addresses starting with 0x800000... will need to be
* specified. Specifying a fixed address is not required on ppc64, i386
* or x86_64.
*/
#include
#include
#include
#include
#include
#define FILE_NAME "/mnt/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
void check_bytes(char *addr)
{
printf("First hex is %x\n", *((unsigned int *)addr));
}
void write_bytes(char *addr)
{
unsigned long i;
for (i = 0; i < LENGTH; i++)
*(addr + i) = (char)i;
}
void 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);
break;
}
}
int main(void)
{
void *addr;
int fd;
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);
read_bytes(addr);
munmap(addr, LENGTH);
close(fd);
unlink(FILE_NAME);
return 0;
}
