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-rw-r--r--Documentation/vm/hugetlbpage.txt169
1 files changed, 2 insertions, 167 deletions
diff --git a/Documentation/vm/hugetlbpage.txt b/Documentation/vm/hugetlbpage.txt
index bc31636973e3..457634c1e03e 100644
--- a/Documentation/vm/hugetlbpage.txt
+++ b/Documentation/vm/hugetlbpage.txt
@@ -299,176 +299,11 @@ map_hugetlb.c.
299******************************************************************* 299*******************************************************************
300 300
301/* 301/*
302 * Example of using huge page memory in a user application using Sys V shared 302 * hugepage-shm: see Documentation/vm/hugepage-shm.c
303 * memory system calls. In this example the app is requesting 256MB of
304 * memory that is backed by huge pages. The application uses the flag
305 * SHM_HUGETLB in the shmget system call to inform the kernel that it is
306 * requesting huge pages.
307 *
308 * For the ia64 architecture, the Linux kernel reserves Region number 4 for
309 * huge pages. That means that if one requires a fixed address, a huge page
310 * aligned address starting with 0x800000... will be required. If a fixed
311 * address is not required, the kernel will select an address in the proper
312 * range.
313 * Other architectures, such as ppc64, i386 or x86_64 are not so constrained.
314 *
315 * Note: The default shared memory limit is quite low on many kernels,
316 * you may need to increase it via:
317 *
318 * echo 268435456 > /proc/sys/kernel/shmmax
319 *
320 * This will increase the maximum size per shared memory segment to 256MB.
321 * The other limit that you will hit eventually is shmall which is the
322 * total amount of shared memory in pages. To set it to 16GB on a system
323 * with a 4kB pagesize do:
324 *
325 * echo 4194304 > /proc/sys/kernel/shmall
326 */ 303 */
327#include <stdlib.h>
328#include <stdio.h>
329#include <sys/types.h>
330#include <sys/ipc.h>
331#include <sys/shm.h>
332#include <sys/mman.h>
333
334#ifndef SHM_HUGETLB
335#define SHM_HUGETLB 04000
336#endif
337
338#define LENGTH (256UL*1024*1024)
339
340#define dprintf(x) printf(x)
341
342#define ADDR (void *)(0x0UL) /* let kernel choose address */
343#define SHMAT_FLAGS (0)
344
345int main(void)
346{
347 int shmid;
348 unsigned long i;
349 char *shmaddr;
350
351 if ((shmid = shmget(2, LENGTH,
352 SHM_HUGETLB | IPC_CREAT | SHM_R | SHM_W)) < 0) {
353 perror("shmget");
354 exit(1);
355 }
356 printf("shmid: 0x%x\n", shmid);
357
358 shmaddr = shmat(shmid, ADDR, SHMAT_FLAGS);
359 if (shmaddr == (char *)-1) {
360 perror("Shared memory attach failure");
361 shmctl(shmid, IPC_RMID, NULL);
362 exit(2);
363 }
364 printf("shmaddr: %p\n", shmaddr);
365
366 dprintf("Starting the writes:\n");
367 for (i = 0; i < LENGTH; i++) {
368 shmaddr[i] = (char)(i);
369 if (!(i % (1024 * 1024)))
370 dprintf(".");
371 }
372 dprintf("\n");
373
374 dprintf("Starting the Check...");
375 for (i = 0; i < LENGTH; i++)
376 if (shmaddr[i] != (char)i)
377 printf("\nIndex %lu mismatched\n", i);
378 dprintf("Done.\n");
379
380 if (shmdt((const void *)shmaddr) != 0) {
381 perror("Detach failure");
382 shmctl(shmid, IPC_RMID, NULL);
383 exit(3);
384 }
385
386 shmctl(shmid, IPC_RMID, NULL);
387
388 return 0;
389}
390 304
391******************************************************************* 305*******************************************************************
392 306
393/* 307/*
394 * Example of using huge page memory in a user application using the mmap 308 * hugepage-mmap: see Documentation/vm/hugepage-mmap.c
395 * system call. Before running this application, make sure that the
396 * administrator has mounted the hugetlbfs filesystem (on some directory
397 * like /mnt) using the command mount -t hugetlbfs nodev /mnt. In this
398 * example, the app is requesting memory of size 256MB that is backed by
399 * huge pages.
400 *
401 * For the ia64 architecture, the Linux kernel reserves Region number 4 for
402 * huge pages. That means that if one requires a fixed address, a huge page
403 * aligned address starting with 0x800000... will be required. If a fixed
404 * address is not required, the kernel will select an address in the proper
405 * range.
406 * Other architectures, such as ppc64, i386 or x86_64 are not so constrained.
407 */ 309 */
408#include <stdlib.h>
409#include <stdio.h>
410#include <unistd.h>
411#include <sys/mman.h>
412#include <fcntl.h>
413
414#define FILE_NAME "/mnt/hugepagefile"
415#define LENGTH (256UL*1024*1024)
416#define PROTECTION (PROT_READ | PROT_WRITE)
417
418#define ADDR (void *)(0x0UL) /* let kernel choose address */
419#define FLAGS (MAP_SHARED)
420
421void check_bytes(char *addr)
422{
423 printf("First hex is %x\n", *((unsigned int *)addr));
424}
425
426void write_bytes(char *addr)
427{
428 unsigned long i;
429
430 for (i = 0; i < LENGTH; i++)
431 *(addr + i) = (char)i;
432}
433
434void read_bytes(char *addr)
435{
436 unsigned long i;
437
438 check_bytes(addr);
439 for (i = 0; i < LENGTH; i++)
440 if (*(addr + i) != (char)i) {
441 printf("Mismatch at %lu\n", i);
442 break;
443 }
444}
445
446int main(void)
447{
448 void *addr;
449 int fd;
450
451 fd = open(FILE_NAME, O_CREAT | O_RDWR, 0755);
452 if (fd < 0) {
453 perror("Open failed");
454 exit(1);
455 }
456
457 addr = mmap(ADDR, LENGTH, PROTECTION, FLAGS, fd, 0);
458 if (addr == MAP_FAILED) {
459 perror("mmap");
460 unlink(FILE_NAME);
461 exit(1);
462 }
463
464 printf("Returned address is %p\n", addr);
465 check_bytes(addr);
466 write_bytes(addr);
467 read_bytes(addr);
468
469 munmap(addr, LENGTH);
470 close(fd);
471 unlink(FILE_NAME);
472
473 return 0;
474}