1 /* 2 * linux/mm/swapfile.c 3 * 4 * Copyright (C) 1991, 1992, 1993, 1994 Linus Torvalds 5 * Swap reorganised 29.12.95, Stephen Tweedie 6 */ 7 8 #include <linux/mm.h> 9 #include <linux/hugetlb.h> 10 #include <linux/mman.h> 11 #include <linux/slab.h> 12 #include <linux/kernel_stat.h> 13 #include <linux/swap.h> 14 #include <linux/vmalloc.h> 15 #include <linux/pagemap.h> 16 #include <linux/namei.h> 17 #include <linux/shm.h> 18 #include <linux/blkdev.h> 19 #include <linux/random.h> 20 #include <linux/writeback.h> 21 #include <linux/proc_fs.h> 22 #include <linux/seq_file.h> 23 #include <linux/init.h> 24 #include <linux/module.h> 25 #include <linux/ksm.h> 26 #include <linux/rmap.h> 27 #include <linux/security.h> 28 #include <linux/backing-dev.h> 29 #include <linux/mutex.h> 30 #include <linux/capability.h> 31 #include <linux/syscalls.h> 32 #include <linux/memcontrol.h> 33 34 #include <asm/pgtable.h> 35 #include <asm/tlbflush.h> 36 #include <linux/swapops.h> 37 #include <linux/page_cgroup.h> 38 39 static bool swap_count_continued(struct swap_info_struct *, pgoff_t, 40 unsigned char); 41 static void free_swap_count_continuations(struct swap_info_struct *); 42 static sector_t map_swap_entry(swp_entry_t, struct block_device**); 43 44 static DEFINE_SPINLOCK(swap_lock); 45 static unsigned int nr_swapfiles; 46 long nr_swap_pages; 47 long total_swap_pages; 48 static int least_priority; 49 50 static const char Bad_file[] = "Bad swap file entry "; 51 static const char Unused_file[] = "Unused swap file entry "; 52 static const char Bad_offset[] = "Bad swap offset entry "; 53 static const char Unused_offset[] = "Unused swap offset entry "; 54 55 static struct swap_list_t swap_list = {-1, -1}; 56 57 static struct swap_info_struct *swap_info[MAX_SWAPFILES]; 58 59 static DEFINE_MUTEX(swapon_mutex); 60 61 static inline unsigned char swap_count(unsigned char ent) 62 { 63 return ent & ~SWAP_HAS_CACHE; /* may include SWAP_HAS_CONT flag */ 64 } 65 66 /* returns 1 if swap entry is freed */ 67 static int 68 __try_to_reclaim_swap(struct swap_info_struct *si, unsigned long offset) 69 { 70 swp_entry_t entry = swp_entry(si->type, offset); 71 struct page *page; 72 int ret = 0; 73 74 page = find_get_page(&swapper_space, entry.val); 75 if (!page) 76 return 0; 77 /* 78 * This function is called from scan_swap_map() and it's called 79 * by vmscan.c at reclaiming pages. So, we hold a lock on a page, here. 80 * We have to use trylock for avoiding deadlock. This is a special 81 * case and you should use try_to_free_swap() with explicit lock_page() 82 * in usual operations. 83 */ 84 if (trylock_page(page)) { 85 ret = try_to_free_swap(page); 86 unlock_page(page); 87 } 88 page_cache_release(page); 89 return ret; 90 } 91 92 /* 93 * We need this because the bdev->unplug_fn can sleep and we cannot 94 * hold swap_lock while calling the unplug_fn. And swap_lock 95 * cannot be turned into a mutex. 96 */ 97 static DECLARE_RWSEM(swap_unplug_sem); 98 99 void swap_unplug_io_fn(struct backing_dev_info *unused_bdi, struct page *page) 100 { 101 swp_entry_t entry; 102 103 down_read(&swap_unplug_sem); 104 entry.val = page_private(page); 105 if (PageSwapCache(page)) { 106 struct block_device *bdev = swap_info[swp_type(entry)]->bdev; 107 struct backing_dev_info *bdi; 108 109 /* 110 * If the page is removed from swapcache from under us (with a 111 * racy try_to_unuse/swapoff) we need an additional reference 112 * count to avoid reading garbage from page_private(page) above. 113 * If the WARN_ON triggers during a swapoff it maybe the race 114 * condition and it's harmless. However if it triggers without 115 * swapoff it signals a problem. 116 */ 117 WARN_ON(page_count(page) <= 1); 118 119 bdi = bdev->bd_inode->i_mapping->backing_dev_info; 120 blk_run_backing_dev(bdi, page); 121 } 122 up_read(&swap_unplug_sem); 123 } 124 125 /* 126 * swapon tell device that all the old swap contents can be discarded, 127 * to allow the swap device to optimize its wear-levelling. 128 */ 129 static int discard_swap(struct swap_info_struct *si) 130 { 131 struct swap_extent *se; 132 sector_t start_block; 133 sector_t nr_blocks; 134 int err = 0; 135 136 /* Do not discard the swap header page! */ 137 se = &si->first_swap_extent; 138 start_block = (se->start_block + 1) << (PAGE_SHIFT - 9); 139 nr_blocks = ((sector_t)se->nr_pages - 1) << (PAGE_SHIFT - 9); 140 if (nr_blocks) { 141 err = blkdev_issue_discard(si->bdev, start_block, 142 nr_blocks, GFP_KERNEL, 0); 143 if (err) 144 return err; 145 cond_resched(); 146 } 147 148 list_for_each_entry(se, &si->first_swap_extent.list, list) { 149 start_block = se->start_block << (PAGE_SHIFT - 9); 150 nr_blocks = (sector_t)se->nr_pages << (PAGE_SHIFT - 9); 151 152 err = blkdev_issue_discard(si->bdev, start_block, 153 nr_blocks, GFP_KERNEL, 0); 154 if (err) 155 break; 156 157 cond_resched(); 158 } 159 return err; /* That will often be -EOPNOTSUPP */ 160 } 161 162 /* 163 * swap allocation tell device that a cluster of swap can now be discarded, 164 * to allow the swap device to optimize its wear-levelling. 165 */ 166 static void discard_swap_cluster(struct swap_info_struct *si, 167 pgoff_t start_page, pgoff_t nr_pages) 168 { 169 struct swap_extent *se = si->curr_swap_extent; 170 int found_extent = 0; 171 172 while (nr_pages) { 173 struct list_head *lh; 174 175 if (se->start_page <= start_page && 176 start_page < se->start_page + se->nr_pages) { 177 pgoff_t offset = start_page - se->start_page; 178 sector_t start_block = se->start_block + offset; 179 sector_t nr_blocks = se->nr_pages - offset; 180 181 if (nr_blocks > nr_pages) 182 nr_blocks = nr_pages; 183 start_page += nr_blocks; 184 nr_pages -= nr_blocks; 185 186 if (!found_extent++) 187 si->curr_swap_extent = se; 188 189 start_block <<= PAGE_SHIFT - 9; 190 nr_blocks <<= PAGE_SHIFT - 9; 191 if (blkdev_issue_discard(si->bdev, start_block, 192 nr_blocks, GFP_NOIO, 0)) 193 break; 194 } 195 196 lh = se->list.next; 197 se = list_entry(lh, struct swap_extent, list); 198 } 199 } 200 201 static int wait_for_discard(void *word) 202 { 203 schedule(); 204 return 0; 205 } 206 207 #define SWAPFILE_CLUSTER 256 208 #define LATENCY_LIMIT 256 209 210 static inline unsigned long scan_swap_map(struct swap_info_struct *si, 211 unsigned char usage) 212 { 213 unsigned long offset; 214 unsigned long scan_base; 215 unsigned long last_in_cluster = 0; 216 int latency_ration = LATENCY_LIMIT; 217 int found_free_cluster = 0; 218 219 /* 220 * We try to cluster swap pages by allocating them sequentially 221 * in swap. Once we've allocated SWAPFILE_CLUSTER pages this 222 * way, however, we resort to first-free allocation, starting 223 * a new cluster. This prevents us from scattering swap pages 224 * all over the entire swap partition, so that we reduce 225 * overall disk seek times between swap pages. -- sct 226 * But we do now try to find an empty cluster. -Andrea 227 * And we let swap pages go all over an SSD partition. Hugh 228 */ 229 230 si->flags += SWP_SCANNING; 231 scan_base = offset = si->cluster_next; 232 233 if (unlikely(!si->cluster_nr--)) { 234 if (si->pages - si->inuse_pages < SWAPFILE_CLUSTER) { 235 si->cluster_nr = SWAPFILE_CLUSTER - 1; 236 goto checks; 237 } 238 if (si->flags & SWP_DISCARDABLE) { 239 /* 240 * Start range check on racing allocations, in case 241 * they overlap the cluster we eventually decide on 242 * (we scan without swap_lock to allow preemption). 243 * It's hardly conceivable that cluster_nr could be 244 * wrapped during our scan, but don't depend on it. 245 */ 246 if (si->lowest_alloc) 247 goto checks; 248 si->lowest_alloc = si->max; 249 si->highest_alloc = 0; 250 } 251 spin_unlock(&swap_lock); 252 253 /* 254 * If seek is expensive, start searching for new cluster from 255 * start of partition, to minimize the span of allocated swap. 256 * But if seek is cheap, search from our current position, so 257 * that swap is allocated from all over the partition: if the 258 * Flash Translation Layer only remaps within limited zones, 259 * we don't want to wear out the first zone too quickly. 260 */ 261 if (!(si->flags & SWP_SOLIDSTATE)) 262 scan_base = offset = si->lowest_bit; 263 last_in_cluster = offset + SWAPFILE_CLUSTER - 1; 264 265 /* Locate the first empty (unaligned) cluster */ 266 for (; last_in_cluster <= si->highest_bit; offset++) { 267 if (si->swap_map[offset]) 268 last_in_cluster = offset + SWAPFILE_CLUSTER; 269 else if (offset == last_in_cluster) { 270 spin_lock(&swap_lock); 271 offset -= SWAPFILE_CLUSTER - 1; 272 si->cluster_next = offset; 273 si->cluster_nr = SWAPFILE_CLUSTER - 1; 274 found_free_cluster = 1; 275 goto checks; 276 } 277 if (unlikely(--latency_ration < 0)) { 278 cond_resched(); 279 latency_ration = LATENCY_LIMIT; 280 } 281 } 282 283 offset = si->lowest_bit; 284 last_in_cluster = offset + SWAPFILE_CLUSTER - 1; 285 286 /* Locate the first empty (unaligned) cluster */ 287 for (; last_in_cluster < scan_base; offset++) { 288 if (si->swap_map[offset]) 289 last_in_cluster = offset + SWAPFILE_CLUSTER; 290 else if (offset == last_in_cluster) { 291 spin_lock(&swap_lock); 292 offset -= SWAPFILE_CLUSTER - 1; 293 si->cluster_next = offset; 294 si->cluster_nr = SWAPFILE_CLUSTER - 1; 295 found_free_cluster = 1; 296 goto checks; 297 } 298 if (unlikely(--latency_ration < 0)) { 299 cond_resched(); 300 latency_ration = LATENCY_LIMIT; 301 } 302 } 303 304 offset = scan_base; 305 spin_lock(&swap_lock); 306 si->cluster_nr = SWAPFILE_CLUSTER - 1; 307 si->lowest_alloc = 0; 308 } 309 310 checks: 311 if (!(si->flags & SWP_WRITEOK)) 312 goto no_page; 313 if (!si->highest_bit) 314 goto no_page; 315 if (offset > si->highest_bit) 316 scan_base = offset = si->lowest_bit; 317 318 /* reuse swap entry of cache-only swap if not busy. */ 319 if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) { 320 int swap_was_freed; 321 spin_unlock(&swap_lock); 322 swap_was_freed = __try_to_reclaim_swap(si, offset); 323 spin_lock(&swap_lock); 324 /* entry was freed successfully, try to use this again */ 325 if (swap_was_freed) 326 goto checks; 327 goto scan; /* check next one */ 328 } 329 330 if (si->swap_map[offset]) 331 goto scan; 332 333 if (offset == si->lowest_bit) 334 si->lowest_bit++; 335 if (offset == si->highest_bit) 336 si->highest_bit--; 337 si->inuse_pages++; 338 if (si->inuse_pages == si->pages) { 339 si->lowest_bit = si->max; 340 si->highest_bit = 0; 341 } 342 si->swap_map[offset] = usage; 343 si->cluster_next = offset + 1; 344 si->flags -= SWP_SCANNING; 345 346 if (si->lowest_alloc) { 347 /* 348 * Only set when SWP_DISCARDABLE, and there's a scan 349 * for a free cluster in progress or just completed. 350 */ 351 if (found_free_cluster) { 352 /* 353 * To optimize wear-levelling, discard the 354 * old data of the cluster, taking care not to 355 * discard any of its pages that have already 356 * been allocated by racing tasks (offset has 357 * already stepped over any at the beginning). 358 */ 359 if (offset < si->highest_alloc && 360 si->lowest_alloc <= last_in_cluster) 361 last_in_cluster = si->lowest_alloc - 1; 362 si->flags |= SWP_DISCARDING; 363 spin_unlock(&swap_lock); 364 365 if (offset < last_in_cluster) 366 discard_swap_cluster(si, offset, 367 last_in_cluster - offset + 1); 368 369 spin_lock(&swap_lock); 370 si->lowest_alloc = 0; 371 si->flags &= ~SWP_DISCARDING; 372 373 smp_mb(); /* wake_up_bit advises this */ 374 wake_up_bit(&si->flags, ilog2(SWP_DISCARDING)); 375 376 } else if (si->flags & SWP_DISCARDING) { 377 /* 378 * Delay using pages allocated by racing tasks 379 * until the whole discard has been issued. We 380 * could defer that delay until swap_writepage, 381 * but it's easier to keep this self-contained. 382 */ 383 spin_unlock(&swap_lock); 384 wait_on_bit(&si->flags, ilog2(SWP_DISCARDING), 385 wait_for_discard, TASK_UNINTERRUPTIBLE); 386 spin_lock(&swap_lock); 387 } else { 388 /* 389 * Note pages allocated by racing tasks while 390 * scan for a free cluster is in progress, so 391 * that its final discard can exclude them. 392 */ 393 if (offset < si->lowest_alloc) 394 si->lowest_alloc = offset; 395 if (offset > si->highest_alloc) 396 si->highest_alloc = offset; 397 } 398 } 399 return offset; 400 401 scan: 402 spin_unlock(&swap_lock); 403 while (++offset <= si->highest_bit) { 404 if (!si->swap_map[offset]) { 405 spin_lock(&swap_lock); 406 goto checks; 407 } 408 if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) { 409 spin_lock(&swap_lock); 410 goto checks; 411 } 412 if (unlikely(--latency_ration < 0)) { 413 cond_resched(); 414 latency_ration = LATENCY_LIMIT; 415 } 416 } 417 offset = si->lowest_bit; 418 while (++offset < scan_base) { 419 if (!si->swap_map[offset]) { 420 spin_lock(&swap_lock); 421 goto checks; 422 } 423 if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) { 424 spin_lock(&swap_lock); 425 goto checks; 426 } 427 if (unlikely(--latency_ration < 0)) { 428 cond_resched(); 429 latency_ration = LATENCY_LIMIT; 430 } 431 } 432 spin_lock(&swap_lock); 433 434 no_page: 435 si->flags -= SWP_SCANNING; 436 return 0; 437 } 438 439 swp_entry_t get_swap_page(void) 440 { 441 struct swap_info_struct *si; 442 pgoff_t offset; 443 int type, next; 444 int wrapped = 0; 445 446 spin_lock(&swap_lock); 447 if (nr_swap_pages <= 0) 448 goto noswap; 449 nr_swap_pages--; 450 451 for (type = swap_list.next; type >= 0 && wrapped < 2; type = next) { 452 si = swap_info[type]; 453 next = si->next; 454 if (next < 0 || 455 (!wrapped && si->prio != swap_info[next]->prio)) { 456 next = swap_list.head; 457 wrapped++; 458 } 459 460 if (!si->highest_bit) 461 continue; 462 if (!(si->flags & SWP_WRITEOK)) 463 continue; 464 465 swap_list.next = next; 466 /* This is called for allocating swap entry for cache */ 467 offset = scan_swap_map(si, SWAP_HAS_CACHE); 468 if (offset) { 469 spin_unlock(&swap_lock); 470 return swp_entry(type, offset); 471 } 472 next = swap_list.next; 473 } 474 475 nr_swap_pages++; 476 noswap: 477 spin_unlock(&swap_lock); 478 return (swp_entry_t) {0}; 479 } 480 481 /* The only caller of this function is now susupend routine */ 482 swp_entry_t get_swap_page_of_type(int type) 483 { 484 struct swap_info_struct *si; 485 pgoff_t offset; 486 487 spin_lock(&swap_lock); 488 si = swap_info[type]; 489 if (si && (si->flags & SWP_WRITEOK)) { 490 nr_swap_pages--; 491 /* This is called for allocating swap entry, not cache */ 492 offset = scan_swap_map(si, 1); 493 if (offset) { 494 spin_unlock(&swap_lock); 495 return swp_entry(type, offset); 496 } 497 nr_swap_pages++; 498 } 499 spin_unlock(&swap_lock); 500 return (swp_entry_t) {0}; 501 } 502 503 static struct swap_info_struct *swap_info_get(swp_entry_t entry) 504 { 505 struct swap_info_struct *p; 506 unsigned long offset, type; 507 508 if (!entry.val) 509 goto out; 510 type = swp_type(entry); 511 if (type >= nr_swapfiles) 512 goto bad_nofile; 513 p = swap_info[type]; 514 if (!(p->flags & SWP_USED)) 515 goto bad_device; 516 offset = swp_offset(entry); 517 if (offset >= p->max) 518 goto bad_offset; 519 if (!p->swap_map[offset]) 520 goto bad_free; 521 spin_lock(&swap_lock); 522 return p; 523 524 bad_free: 525 printk(KERN_ERR "swap_free: %s%08lx\n", Unused_offset, entry.val); 526 goto out; 527 bad_offset: 528 printk(KERN_ERR "swap_free: %s%08lx\n", Bad_offset, entry.val); 529 goto out; 530 bad_device: 531 printk(KERN_ERR "swap_free: %s%08lx\n", Unused_file, entry.val); 532 goto out; 533 bad_nofile: 534 printk(KERN_ERR "swap_free: %s%08lx\n", Bad_file, entry.val); 535 out: 536 return NULL; 537 } 538 539 static unsigned char swap_entry_free(struct swap_info_struct *p, 540 swp_entry_t entry, unsigned char usage) 541 { 542 unsigned long offset = swp_offset(entry); 543 unsigned char count; 544 unsigned char has_cache; 545 546 count = p->swap_map[offset]; 547 has_cache = count & SWAP_HAS_CACHE; 548 count &= ~SWAP_HAS_CACHE; 549 550 if (usage == SWAP_HAS_CACHE) { 551 VM_BUG_ON(!has_cache); 552 has_cache = 0; 553 } else if (count == SWAP_MAP_SHMEM) { 554 /* 555 * Or we could insist on shmem.c using a special 556 * swap_shmem_free() and free_shmem_swap_and_cache()... 557 */ 558 count = 0; 559 } else if ((count & ~COUNT_CONTINUED) <= SWAP_MAP_MAX) { 560 if (count == COUNT_CONTINUED) { 561 if (swap_count_continued(p, offset, count)) 562 count = SWAP_MAP_MAX | COUNT_CONTINUED; 563 else 564 count = SWAP_MAP_MAX; 565 } else 566 count--; 567 } 568 569 if (!count) 570 mem_cgroup_uncharge_swap(entry); 571 572 usage = count | has_cache; 573 p->swap_map[offset] = usage; 574 575 /* free if no reference */ 576 if (!usage) { 577 struct gendisk *disk = p->bdev->bd_disk; 578 if (offset < p->lowest_bit) 579 p->lowest_bit = offset; 580 if (offset > p->highest_bit) 581 p->highest_bit = offset; 582 if (swap_list.next >= 0 && 583 p->prio > swap_info[swap_list.next]->prio) 584 swap_list.next = p->type; 585 nr_swap_pages++; 586 p->inuse_pages--; 587 if ((p->flags & SWP_BLKDEV) && 588 disk->fops->swap_slot_free_notify) 589 disk->fops->swap_slot_free_notify(p->bdev, offset); 590 } 591 592 return usage; 593 } 594 595 /* 596 * Caller has made sure that the swapdevice corresponding to entry 597 * is still around or has not been recycled. 598 */ 599 void swap_free(swp_entry_t entry) 600 { 601 struct swap_info_struct *p; 602 603 p = swap_info_get(entry); 604 if (p) { 605 swap_entry_free(p, entry, 1); 606 spin_unlock(&swap_lock); 607 } 608 } 609 610 /* 611 * Called after dropping swapcache to decrease refcnt to swap entries. 612 */ 613 void swapcache_free(swp_entry_t entry, struct page *page) 614 { 615 struct swap_info_struct *p; 616 unsigned char count; 617 618 p = swap_info_get(entry); 619 if (p) { 620 count = swap_entry_free(p, entry, SWAP_HAS_CACHE); 621 if (page) 622 mem_cgroup_uncharge_swapcache(page, entry, count != 0); 623 spin_unlock(&swap_lock); 624 } 625 } 626 627 /* 628 * How many references to page are currently swapped out? 629 * This does not give an exact answer when swap count is continued, 630 * but does include the high COUNT_CONTINUED flag to allow for that. 631 */ 632 static inline int page_swapcount(struct page *page) 633 { 634 int count = 0; 635 struct swap_info_struct *p; 636 swp_entry_t entry; 637 638 entry.val = page_private(page); 639 p = swap_info_get(entry); 640 if (p) { 641 count = swap_count(p->swap_map[swp_offset(entry)]); 642 spin_unlock(&swap_lock); 643 } 644 return count; 645 } 646 647 /* 648 * We can write to an anon page without COW if there are no other references 649 * to it. And as a side-effect, free up its swap: because the old content 650 * on disk will never be read, and seeking back there to write new content 651 * later would only waste time away from clustering. 652 */ 653 int reuse_swap_page(struct page *page) 654 { 655 int count; 656 657 VM_BUG_ON(!PageLocked(page)); 658 if (unlikely(PageKsm(page))) 659 return 0; 660 count = page_mapcount(page); 661 if (count <= 1 && PageSwapCache(page)) { 662 count += page_swapcount(page); 663 if (count == 1 && !PageWriteback(page)) { 664 delete_from_swap_cache(page); 665 SetPageDirty(page); 666 } 667 } 668 return count <= 1; 669 } 670 671 /* 672 * If swap is getting full, or if there are no more mappings of this page, 673 * then try_to_free_swap is called to free its swap space. 674 */ 675 int try_to_free_swap(struct page *page) 676 { 677 VM_BUG_ON(!PageLocked(page)); 678 679 if (!PageSwapCache(page)) 680 return 0; 681 if (PageWriteback(page)) 682 return 0; 683 if (page_swapcount(page)) 684 return 0; 685 686 /* 687 * Once hibernation has begun to create its image of memory, 688 * there's a danger that one of the calls to try_to_free_swap() 689 * - most probably a call from __try_to_reclaim_swap() while 690 * hibernation is allocating its own swap pages for the image, 691 * but conceivably even a call from memory reclaim - will free 692 * the swap from a page which has already been recorded in the 693 * image as a clean swapcache page, and then reuse its swap for 694 * another page of the image. On waking from hibernation, the 695 * original page might be freed under memory pressure, then 696 * later read back in from swap, now with the wrong data. 697 * 698 * Hibernation clears bits from gfp_allowed_mask to prevent 699 * memory reclaim from writing to disk, so check that here. 700 */ 701 if (!(gfp_allowed_mask & __GFP_IO)) 702 return 0; 703 704 delete_from_swap_cache(page); 705 SetPageDirty(page); 706 return 1; 707 } 708 709 /* 710 * Free the swap entry like above, but also try to 711 * free the page cache entry if it is the last user. 712 */ 713 int free_swap_and_cache(swp_entry_t entry) 714 { 715 struct swap_info_struct *p; 716 struct page *page = NULL; 717 718 if (non_swap_entry(entry)) 719 return 1; 720 721 p = swap_info_get(entry); 722 if (p) { 723 if (swap_entry_free(p, entry, 1) == SWAP_HAS_CACHE) { 724 page = find_get_page(&swapper_space, entry.val); 725 if (page && !trylock_page(page)) { 726 page_cache_release(page); 727 page = NULL; 728 } 729 } 730 spin_unlock(&swap_lock); 731 } 732 if (page) { 733 /* 734 * Not mapped elsewhere, or swap space full? Free it! 735 * Also recheck PageSwapCache now page is locked (above). 736 */ 737 if (PageSwapCache(page) && !PageWriteback(page) && 738 (!page_mapped(page) || vm_swap_full())) { 739 delete_from_swap_cache(page); 740 SetPageDirty(page); 741 } 742 unlock_page(page); 743 page_cache_release(page); 744 } 745 return p != NULL; 746 } 747 748 #ifdef CONFIG_CGROUP_MEM_RES_CTLR 749 /** 750 * mem_cgroup_count_swap_user - count the user of a swap entry 751 * @ent: the swap entry to be checked 752 * @pagep: the pointer for the swap cache page of the entry to be stored 753 * 754 * Returns the number of the user of the swap entry. The number is valid only 755 * for swaps of anonymous pages. 756 * If the entry is found on swap cache, the page is stored to pagep with 757 * refcount of it being incremented. 758 */ 759 int mem_cgroup_count_swap_user(swp_entry_t ent, struct page **pagep) 760 { 761 struct page *page; 762 struct swap_info_struct *p; 763 int count = 0; 764 765 page = find_get_page(&swapper_space, ent.val); 766 if (page) 767 count += page_mapcount(page); 768 p = swap_info_get(ent); 769 if (p) { 770 count += swap_count(p->swap_map[swp_offset(ent)]); 771 spin_unlock(&swap_lock); 772 } 773 774 *pagep = page; 775 return count; 776 } 777 #endif 778 779 #ifdef CONFIG_HIBERNATION 780 /* 781 * Find the swap type that corresponds to given device (if any). 782 * 783 * @offset - number of the PAGE_SIZE-sized block of the device, starting 784 * from 0, in which the swap header is expected to be located. 785 * 786 * This is needed for the suspend to disk (aka swsusp). 787 */ 788 int swap_type_of(dev_t device, sector_t offset, struct block_device **bdev_p) 789 { 790 struct block_device *bdev = NULL; 791 int type; 792 793 if (device) 794 bdev = bdget(device); 795 796 spin_lock(&swap_lock); 797 for (type = 0; type < nr_swapfiles; type++) { 798 struct swap_info_struct *sis = swap_info[type]; 799 800 if (!(sis->flags & SWP_WRITEOK)) 801 continue; 802 803 if (!bdev) { 804 if (bdev_p) 805 *bdev_p = bdgrab(sis->bdev); 806 807 spin_unlock(&swap_lock); 808 return type; 809 } 810 if (bdev == sis->bdev) { 811 struct swap_extent *se = &sis->first_swap_extent; 812 813 if (se->start_block == offset) { 814 if (bdev_p) 815 *bdev_p = bdgrab(sis->bdev); 816 817 spin_unlock(&swap_lock); 818 bdput(bdev); 819 return type; 820 } 821 } 822 } 823 spin_unlock(&swap_lock); 824 if (bdev) 825 bdput(bdev); 826 827 return -ENODEV; 828 } 829 830 /* 831 * Get the (PAGE_SIZE) block corresponding to given offset on the swapdev 832 * corresponding to given index in swap_info (swap type). 833 */ 834 sector_t swapdev_block(int type, pgoff_t offset) 835 { 836 struct block_device *bdev; 837 838 if ((unsigned int)type >= nr_swapfiles) 839 return 0; 840 if (!(swap_info[type]->flags & SWP_WRITEOK)) 841 return 0; 842 return map_swap_entry(swp_entry(type, offset), &bdev); 843 } 844 845 /* 846 * Return either the total number of swap pages of given type, or the number 847 * of free pages of that type (depending on @free) 848 * 849 * This is needed for software suspend 850 */ 851 unsigned int count_swap_pages(int type, int free) 852 { 853 unsigned int n = 0; 854 855 spin_lock(&swap_lock); 856 if ((unsigned int)type < nr_swapfiles) { 857 struct swap_info_struct *sis = swap_info[type]; 858 859 if (sis->flags & SWP_WRITEOK) { 860 n = sis->pages; 861 if (free) 862 n -= sis->inuse_pages; 863 } 864 } 865 spin_unlock(&swap_lock); 866 return n; 867 } 868 #endif /* CONFIG_HIBERNATION */ 869 870 /* 871 * No need to decide whether this PTE shares the swap entry with others, 872 * just let do_wp_page work it out if a write is requested later - to 873 * force COW, vm_page_prot omits write permission from any private vma. 874 */ 875 static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd, 876 unsigned long addr, swp_entry_t entry, struct page *page) 877 { 878 struct mem_cgroup *ptr = NULL; 879 spinlock_t *ptl; 880 pte_t *pte; 881 int ret = 1; 882 883 if (mem_cgroup_try_charge_swapin(vma->vm_mm, page, GFP_KERNEL, &ptr)) { 884 ret = -ENOMEM; 885 goto out_nolock; 886 } 887 888 pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl); 889 if (unlikely(!pte_same(*pte, swp_entry_to_pte(entry)))) { 890 if (ret > 0) 891 mem_cgroup_cancel_charge_swapin(ptr); 892 ret = 0; 893 goto out; 894 } 895 896 dec_mm_counter(vma->vm_mm, MM_SWAPENTS); 897 inc_mm_counter(vma->vm_mm, MM_ANONPAGES); 898 get_page(page); 899 set_pte_at(vma->vm_mm, addr, pte, 900 pte_mkold(mk_pte(page, vma->vm_page_prot))); 901 page_add_anon_rmap(page, vma, addr); 902 mem_cgroup_commit_charge_swapin(page, ptr); 903 swap_free(entry); 904 /* 905 * Move the page to the active list so it is not 906 * immediately swapped out again after swapon. 907 */ 908 activate_page(page); 909 out: 910 pte_unmap_unlock(pte, ptl); 911 out_nolock: 912 return ret; 913 } 914 915 static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd, 916 unsigned long addr, unsigned long end, 917 swp_entry_t entry, struct page *page) 918 { 919 pte_t swp_pte = swp_entry_to_pte(entry); 920 pte_t *pte; 921 int ret = 0; 922 923 /* 924 * We don't actually need pte lock while scanning for swp_pte: since 925 * we hold page lock and mmap_sem, swp_pte cannot be inserted into the 926 * page table while we're scanning; though it could get zapped, and on 927 * some architectures (e.g. x86_32 with PAE) we might catch a glimpse 928 * of unmatched parts which look like swp_pte, so unuse_pte must 929 * recheck under pte lock. Scanning without pte lock lets it be 930 * preemptible whenever CONFIG_PREEMPT but not CONFIG_HIGHPTE. 931 */ 932 pte = pte_offset_map(pmd, addr); 933 do { 934 /* 935 * swapoff spends a _lot_ of time in this loop! 936 * Test inline before going to call unuse_pte. 937 */ 938 if (unlikely(pte_same(*pte, swp_pte))) { 939 pte_unmap(pte); 940 ret = unuse_pte(vma, pmd, addr, entry, page); 941 if (ret) 942 goto out; 943 pte = pte_offset_map(pmd, addr); 944 } 945 } while (pte++, addr += PAGE_SIZE, addr != end); 946 pte_unmap(pte - 1); 947 out: 948 return ret; 949 } 950 951 static inline int unuse_pmd_range(struct vm_area_struct *vma, pud_t *pud, 952 unsigned long addr, unsigned long end, 953 swp_entry_t entry, struct page *page) 954 { 955 pmd_t *pmd; 956 unsigned long next; 957 int ret; 958 959 pmd = pmd_offset(pud, addr); 960 do { 961 next = pmd_addr_end(addr, end); 962 if (pmd_none_or_clear_bad(pmd)) 963 continue; 964 ret = unuse_pte_range(vma, pmd, addr, next, entry, page); 965 if (ret) 966 return ret; 967 } while (pmd++, addr = next, addr != end); 968 return 0; 969 } 970 971 static inline int unuse_pud_range(struct vm_area_struct *vma, pgd_t *pgd, 972 unsigned long addr, unsigned long end, 973 swp_entry_t entry, struct page *page) 974 { 975 pud_t *pud; 976 unsigned long next; 977 int ret; 978 979 pud = pud_offset(pgd, addr); 980 do { 981 next = pud_addr_end(addr, end); 982 if (pud_none_or_clear_bad(pud)) 983 continue; 984 ret = unuse_pmd_range(vma, pud, addr, next, entry, page); 985 if (ret) 986 return ret; 987 } while (pud++, addr = next, addr != end); 988 return 0; 989 } 990 991 static int unuse_vma(struct vm_area_struct *vma, 992 swp_entry_t entry, struct page *page) 993 { 994 pgd_t *pgd; 995 unsigned long addr, end, next; 996 int ret; 997 998 if (page_anon_vma(page)) { 999 addr = page_address_in_vma(page, vma); 1000 if (addr == -EFAULT) 1001 return 0; 1002 else 1003 end = addr + PAGE_SIZE; 1004 } else { 1005 addr = vma->vm_start; 1006 end = vma->vm_end; 1007 } 1008 1009 pgd = pgd_offset(vma->vm_mm, addr); 1010 do { 1011 next = pgd_addr_end(addr, end); 1012 if (pgd_none_or_clear_bad(pgd)) 1013 continue; 1014 ret = unuse_pud_range(vma, pgd, addr, next, entry, page); 1015 if (ret) 1016 return ret; 1017 } while (pgd++, addr = next, addr != end); 1018 return 0; 1019 } 1020 1021 static int unuse_mm(struct mm_struct *mm, 1022 swp_entry_t entry, struct page *page) 1023 { 1024 struct vm_area_struct *vma; 1025 int ret = 0; 1026 1027 if (!down_read_trylock(&mm->mmap_sem)) { 1028 /* 1029 * Activate page so shrink_inactive_list is unlikely to unmap 1030 * its ptes while lock is dropped, so swapoff can make progress. 1031 */ 1032 activate_page(page); 1033 unlock_page(page); 1034 down_read(&mm->mmap_sem); 1035 lock_page(page); 1036 } 1037 for (vma = mm->mmap; vma; vma = vma->vm_next) { 1038 if (vma->anon_vma && (ret = unuse_vma(vma, entry, page))) 1039 break; 1040 } 1041 up_read(&mm->mmap_sem); 1042 return (ret < 0)? ret: 0; 1043 } 1044 1045 /* 1046 * Scan swap_map from current position to next entry still in use. 1047 * Recycle to start on reaching the end, returning 0 when empty. 1048 */ 1049 static unsigned int find_next_to_unuse(struct swap_info_struct *si, 1050 unsigned int prev) 1051 { 1052 unsigned int max = si->max; 1053 unsigned int i = prev; 1054 unsigned char count; 1055 1056 /* 1057 * No need for swap_lock here: we're just looking 1058 * for whether an entry is in use, not modifying it; false 1059 * hits are okay, and sys_swapoff() has already prevented new 1060 * allocations from this area (while holding swap_lock). 1061 */ 1062 for (;;) { 1063 if (++i >= max) { 1064 if (!prev) { 1065 i = 0; 1066 break; 1067 } 1068 /* 1069 * No entries in use at top of swap_map, 1070 * loop back to start and recheck there. 1071 */ 1072 max = prev + 1; 1073 prev = 0; 1074 i = 1; 1075 } 1076 count = si->swap_map[i]; 1077 if (count && swap_count(count) != SWAP_MAP_BAD) 1078 break; 1079 } 1080 return i; 1081 } 1082 1083 /* 1084 * We completely avoid races by reading each swap page in advance, 1085 * and then search for the process using it. All the necessary 1086 * page table adjustments can then be made atomically. 1087 */ 1088 static int try_to_unuse(unsigned int type) 1089 { 1090 struct swap_info_struct *si = swap_info[type]; 1091 struct mm_struct *start_mm; 1092 unsigned char *swap_map; 1093 unsigned char swcount; 1094 struct page *page; 1095 swp_entry_t entry; 1096 unsigned int i = 0; 1097 int retval = 0; 1098 1099 /* 1100 * When searching mms for an entry, a good strategy is to 1101 * start at the first mm we freed the previous entry from 1102 * (though actually we don't notice whether we or coincidence 1103 * freed the entry). Initialize this start_mm with a hold. 1104 * 1105 * A simpler strategy would be to start at the last mm we 1106 * freed the previous entry from; but that would take less 1107 * advantage of mmlist ordering, which clusters forked mms 1108 * together, child after parent. If we race with dup_mmap(), we 1109 * prefer to resolve parent before child, lest we miss entries 1110 * duplicated after we scanned child: using last mm would invert 1111 * that. 1112 */ 1113 start_mm = &init_mm; 1114 atomic_inc(&init_mm.mm_users); 1115 1116 /* 1117 * Keep on scanning until all entries have gone. Usually, 1118 * one pass through swap_map is enough, but not necessarily: 1119 * there are races when an instance of an entry might be missed. 1120 */ 1121 while ((i = find_next_to_unuse(si, i)) != 0) { 1122 if (signal_pending(current)) { 1123 retval = -EINTR; 1124 break; 1125 } 1126 1127 /* 1128 * Get a page for the entry, using the existing swap 1129 * cache page if there is one. Otherwise, get a clean 1130 * page and read the swap into it. 1131 */ 1132 swap_map = &si->swap_map[i]; 1133 entry = swp_entry(type, i); 1134 page = read_swap_cache_async(entry, 1135 GFP_HIGHUSER_MOVABLE, NULL, 0); 1136 if (!page) { 1137 /* 1138 * Either swap_duplicate() failed because entry 1139 * has been freed independently, and will not be 1140 * reused since sys_swapoff() already disabled 1141 * allocation from here, or alloc_page() failed. 1142 */ 1143 if (!*swap_map) 1144 continue; 1145 retval = -ENOMEM; 1146 break; 1147 } 1148 1149 /* 1150 * Don't hold on to start_mm if it looks like exiting. 1151 */ 1152 if (atomic_read(&start_mm->mm_users) == 1) { 1153 mmput(start_mm); 1154 start_mm = &init_mm; 1155 atomic_inc(&init_mm.mm_users); 1156 } 1157 1158 /* 1159 * Wait for and lock page. When do_swap_page races with 1160 * try_to_unuse, do_swap_page can handle the fault much 1161 * faster than try_to_unuse can locate the entry. This 1162 * apparently redundant "wait_on_page_locked" lets try_to_unuse 1163 * defer to do_swap_page in such a case - in some tests, 1164 * do_swap_page and try_to_unuse repeatedly compete. 1165 */ 1166 wait_on_page_locked(page); 1167 wait_on_page_writeback(page); 1168 lock_page(page); 1169 wait_on_page_writeback(page); 1170 1171 /* 1172 * Remove all references to entry. 1173 */ 1174 swcount = *swap_map; 1175 if (swap_count(swcount) == SWAP_MAP_SHMEM) { 1176 retval = shmem_unuse(entry, page); 1177 /* page has already been unlocked and released */ 1178 if (retval < 0) 1179 break; 1180 continue; 1181 } 1182 if (swap_count(swcount) && start_mm != &init_mm) 1183 retval = unuse_mm(start_mm, entry, page); 1184 1185 if (swap_count(*swap_map)) { 1186 int set_start_mm = (*swap_map >= swcount); 1187 struct list_head *p = &start_mm->mmlist; 1188 struct mm_struct *new_start_mm = start_mm; 1189 struct mm_struct *prev_mm = start_mm; 1190 struct mm_struct *mm; 1191 1192 atomic_inc(&new_start_mm->mm_users); 1193 atomic_inc(&prev_mm->mm_users); 1194 spin_lock(&mmlist_lock); 1195 while (swap_count(*swap_map) && !retval && 1196 (p = p->next) != &start_mm->mmlist) { 1197 mm = list_entry(p, struct mm_struct, mmlist); 1198 if (!atomic_inc_not_zero(&mm->mm_users)) 1199 continue; 1200 spin_unlock(&mmlist_lock); 1201 mmput(prev_mm); 1202 prev_mm = mm; 1203 1204 cond_resched(); 1205 1206 swcount = *swap_map; 1207 if (!swap_count(swcount)) /* any usage ? */ 1208 ; 1209 else if (mm == &init_mm) 1210 set_start_mm = 1; 1211 else 1212 retval = unuse_mm(mm, entry, page); 1213 1214 if (set_start_mm && *swap_map < swcount) { 1215 mmput(new_start_mm); 1216 atomic_inc(&mm->mm_users); 1217 new_start_mm = mm; 1218 set_start_mm = 0; 1219 } 1220 spin_lock(&mmlist_lock); 1221 } 1222 spin_unlock(&mmlist_lock); 1223 mmput(prev_mm); 1224 mmput(start_mm); 1225 start_mm = new_start_mm; 1226 } 1227 if (retval) { 1228 unlock_page(page); 1229 page_cache_release(page); 1230 break; 1231 } 1232 1233 /* 1234 * If a reference remains (rare), we would like to leave 1235 * the page in the swap cache; but try_to_unmap could 1236 * then re-duplicate the entry once we drop page lock, 1237 * so we might loop indefinitely; also, that page could 1238 * not be swapped out to other storage meanwhile. So: 1239 * delete from cache even if there's another reference, 1240 * after ensuring that the data has been saved to disk - 1241 * since if the reference remains (rarer), it will be 1242 * read from disk into another page. Splitting into two 1243 * pages would be incorrect if swap supported "shared 1244 * private" pages, but they are handled by tmpfs files. 1245 * 1246 * Given how unuse_vma() targets one particular offset 1247 * in an anon_vma, once the anon_vma has been determined, 1248 * this splitting happens to be just what is needed to 1249 * handle where KSM pages have been swapped out: re-reading 1250 * is unnecessarily slow, but we can fix that later on. 1251 */ 1252 if (swap_count(*swap_map) && 1253 PageDirty(page) && PageSwapCache(page)) { 1254 struct writeback_control wbc = { 1255 .sync_mode = WB_SYNC_NONE, 1256 }; 1257 1258 swap_writepage(page, &wbc); 1259 lock_page(page); 1260 wait_on_page_writeback(page); 1261 } 1262 1263 /* 1264 * It is conceivable that a racing task removed this page from 1265 * swap cache just before we acquired the page lock at the top, 1266 * or while we dropped it in unuse_mm(). The page might even 1267 * be back in swap cache on another swap area: that we must not 1268 * delete, since it may not have been written out to swap yet. 1269 */ 1270 if (PageSwapCache(page) && 1271 likely(page_private(page) == entry.val)) 1272 delete_from_swap_cache(page); 1273 1274 /* 1275 * So we could skip searching mms once swap count went 1276 * to 1, we did not mark any present ptes as dirty: must 1277 * mark page dirty so shrink_page_list will preserve it. 1278 */ 1279 SetPageDirty(page); 1280 unlock_page(page); 1281 page_cache_release(page); 1282 1283 /* 1284 * Make sure that we aren't completely killing 1285 * interactive performance. 1286 */ 1287 cond_resched(); 1288 } 1289 1290 mmput(start_mm); 1291 return retval; 1292 } 1293 1294 /* 1295 * After a successful try_to_unuse, if no swap is now in use, we know 1296 * we can empty the mmlist. swap_lock must be held on entry and exit. 1297 * Note that mmlist_lock nests inside swap_lock, and an mm must be 1298 * added to the mmlist just after page_duplicate - before would be racy. 1299 */ 1300 static void drain_mmlist(void) 1301 { 1302 struct list_head *p, *next; 1303 unsigned int type; 1304 1305 for (type = 0; type < nr_swapfiles; type++) 1306 if (swap_info[type]->inuse_pages) 1307 return; 1308 spin_lock(&mmlist_lock); 1309 list_for_each_safe(p, next, &init_mm.mmlist) 1310 list_del_init(p); 1311 spin_unlock(&mmlist_lock); 1312 } 1313 1314 /* 1315 * Use this swapdev's extent info to locate the (PAGE_SIZE) block which 1316 * corresponds to page offset for the specified swap entry. 1317 * Note that the type of this function is sector_t, but it returns page offset 1318 * into the bdev, not sector offset. 1319 */ 1320 static sector_t map_swap_entry(swp_entry_t entry, struct block_device **bdev) 1321 { 1322 struct swap_info_struct *sis; 1323 struct swap_extent *start_se; 1324 struct swap_extent *se; 1325 pgoff_t offset; 1326 1327 sis = swap_info[swp_type(entry)]; 1328 *bdev = sis->bdev; 1329 1330 offset = swp_offset(entry); 1331 start_se = sis->curr_swap_extent; 1332 se = start_se; 1333 1334 for ( ; ; ) { 1335 struct list_head *lh; 1336 1337 if (se->start_page <= offset && 1338 offset < (se->start_page + se->nr_pages)) { 1339 return se->start_block + (offset - se->start_page); 1340 } 1341 lh = se->list.next; 1342 se = list_entry(lh, struct swap_extent, list); 1343 sis->curr_swap_extent = se; 1344 BUG_ON(se == start_se); /* It *must* be present */ 1345 } 1346 } 1347 1348 /* 1349 * Returns the page offset into bdev for the specified page's swap entry. 1350 */ 1351 sector_t map_swap_page(struct page *page, struct block_device **bdev) 1352 { 1353 swp_entry_t entry; 1354 entry.val = page_private(page); 1355 return map_swap_entry(entry, bdev); 1356 } 1357 1358 /* 1359 * Free all of a swapdev's extent information 1360 */ 1361 static void destroy_swap_extents(struct swap_info_struct *sis) 1362 { 1363 while (!list_empty(&sis->first_swap_extent.list)) { 1364 struct swap_extent *se; 1365 1366 se = list_entry(sis->first_swap_extent.list.next, 1367 struct swap_extent, list); 1368 list_del(&se->list); 1369 kfree(se); 1370 } 1371 } 1372 1373 /* 1374 * Add a block range (and the corresponding page range) into this swapdev's 1375 * extent list. The extent list is kept sorted in page order. 1376 * 1377 * This function rather assumes that it is called in ascending page order. 1378 */ 1379 static int 1380 add_swap_extent(struct swap_info_struct *sis, unsigned long start_page, 1381 unsigned long nr_pages, sector_t start_block) 1382 { 1383 struct swap_extent *se; 1384 struct swap_extent *new_se; 1385 struct list_head *lh; 1386 1387 if (start_page == 0) { 1388 se = &sis->first_swap_extent; 1389 sis->curr_swap_extent = se; 1390 se->start_page = 0; 1391 se->nr_pages = nr_pages; 1392 se->start_block = start_block; 1393 return 1; 1394 } else { 1395 lh = sis->first_swap_extent.list.prev; /* Highest extent */ 1396 se = list_entry(lh, struct swap_extent, list); 1397 BUG_ON(se->start_page + se->nr_pages != start_page); 1398 if (se->start_block + se->nr_pages == start_block) { 1399 /* Merge it */ 1400 se->nr_pages += nr_pages; 1401 return 0; 1402 } 1403 } 1404 1405 /* 1406 * No merge. Insert a new extent, preserving ordering. 1407 */ 1408 new_se = kmalloc(sizeof(*se), GFP_KERNEL); 1409 if (new_se == NULL) 1410 return -ENOMEM; 1411 new_se->start_page = start_page; 1412 new_se->nr_pages = nr_pages; 1413 new_se->start_block = start_block; 1414 1415 list_add_tail(&new_se->list, &sis->first_swap_extent.list); 1416 return 1; 1417 } 1418 1419 /* 1420 * A `swap extent' is a simple thing which maps a contiguous range of pages 1421 * onto a contiguous range of disk blocks. An ordered list of swap extents 1422 * is built at swapon time and is then used at swap_writepage/swap_readpage 1423 * time for locating where on disk a page belongs. 1424 * 1425 * If the swapfile is an S_ISBLK block device, a single extent is installed. 1426 * This is done so that the main operating code can treat S_ISBLK and S_ISREG 1427 * swap files identically. 1428 * 1429 * Whether the swapdev is an S_ISREG file or an S_ISBLK blockdev, the swap 1430 * extent list operates in PAGE_SIZE disk blocks. Both S_ISREG and S_ISBLK 1431 * swapfiles are handled *identically* after swapon time. 1432 * 1433 * For S_ISREG swapfiles, setup_swap_extents() will walk all the file's blocks 1434 * and will parse them into an ordered extent list, in PAGE_SIZE chunks. If 1435 * some stray blocks are found which do not fall within the PAGE_SIZE alignment 1436 * requirements, they are simply tossed out - we will never use those blocks 1437 * for swapping. 1438 * 1439 * For S_ISREG swapfiles we set S_SWAPFILE across the life of the swapon. This 1440 * prevents root from shooting her foot off by ftruncating an in-use swapfile, 1441 * which will scribble on the fs. 1442 * 1443 * The amount of disk space which a single swap extent represents varies. 1444 * Typically it is in the 1-4 megabyte range. So we can have hundreds of 1445 * extents in the list. To avoid much list walking, we cache the previous 1446 * search location in `curr_swap_extent', and start new searches from there. 1447 * This is extremely effective. The average number of iterations in 1448 * map_swap_page() has been measured at about 0.3 per page. - akpm. 1449 */ 1450 static int setup_swap_extents(struct swap_info_struct *sis, sector_t *span) 1451 { 1452 struct inode *inode; 1453 unsigned blocks_per_page; 1454 unsigned long page_no; 1455 unsigned blkbits; 1456 sector_t probe_block; 1457 sector_t last_block; 1458 sector_t lowest_block = -1; 1459 sector_t highest_block = 0; 1460 int nr_extents = 0; 1461 int ret; 1462 1463 inode = sis->swap_file->f_mapping->host; 1464 if (S_ISBLK(inode->i_mode)) { 1465 ret = add_swap_extent(sis, 0, sis->max, 0); 1466 *span = sis->pages; 1467 goto out; 1468 } 1469 1470 blkbits = inode->i_blkbits; 1471 blocks_per_page = PAGE_SIZE >> blkbits; 1472 1473 /* 1474 * Map all the blocks into the extent list. This code doesn't try 1475 * to be very smart. 1476 */ 1477 probe_block = 0; 1478 page_no = 0; 1479 last_block = i_size_read(inode) >> blkbits; 1480 while ((probe_block + blocks_per_page) <= last_block && 1481 page_no < sis->max) { 1482 unsigned block_in_page; 1483 sector_t first_block; 1484 1485 first_block = bmap(inode, probe_block); 1486 if (first_block == 0) 1487 goto bad_bmap; 1488 1489 /* 1490 * It must be PAGE_SIZE aligned on-disk 1491 */ 1492 if (first_block & (blocks_per_page - 1)) { 1493 probe_block++; 1494 goto reprobe; 1495 } 1496 1497 for (block_in_page = 1; block_in_page < blocks_per_page; 1498 block_in_page++) { 1499 sector_t block; 1500 1501 block = bmap(inode, probe_block + block_in_page); 1502 if (block == 0) 1503 goto bad_bmap; 1504 if (block != first_block + block_in_page) { 1505 /* Discontiguity */ 1506 probe_block++; 1507 goto reprobe; 1508 } 1509 } 1510 1511 first_block >>= (PAGE_SHIFT - blkbits); 1512 if (page_no) { /* exclude the header page */ 1513 if (first_block < lowest_block) 1514 lowest_block = first_block; 1515 if (first_block > highest_block) 1516 highest_block = first_block; 1517 } 1518 1519 /* 1520 * We found a PAGE_SIZE-length, PAGE_SIZE-aligned run of blocks 1521 */ 1522 ret = add_swap_extent(sis, page_no, 1, first_block); 1523 if (ret < 0) 1524 goto out; 1525 nr_extents += ret; 1526 page_no++; 1527 probe_block += blocks_per_page; 1528 reprobe: 1529 continue; 1530 } 1531 ret = nr_extents; 1532 *span = 1 + highest_block - lowest_block; 1533 if (page_no == 0) 1534 page_no = 1; /* force Empty message */ 1535 sis->max = page_no; 1536 sis->pages = page_no - 1; 1537 sis->highest_bit = page_no - 1; 1538 out: 1539 return ret; 1540 bad_bmap: 1541 printk(KERN_ERR "swapon: swapfile has holes\n"); 1542 ret = -EINVAL; 1543 goto out; 1544 } 1545 1546 SYSCALL_DEFINE1(swapoff, const char __user *, specialfile) 1547 { 1548 struct swap_info_struct *p = NULL; 1549 unsigned char *swap_map; 1550 struct file *swap_file, *victim; 1551 struct address_space *mapping; 1552 struct inode *inode; 1553 char *pathname; 1554 int i, type, prev; 1555 int err; 1556 1557 if (!capable(CAP_SYS_ADMIN)) 1558 return -EPERM; 1559 1560 pathname = getname(specialfile); 1561 err = PTR_ERR(pathname); 1562 if (IS_ERR(pathname)) 1563 goto out; 1564 1565 victim = filp_open(pathname, O_RDWR|O_LARGEFILE, 0); 1566 putname(pathname); 1567 err = PTR_ERR(victim); 1568 if (IS_ERR(victim)) 1569 goto out; 1570 1571 mapping = victim->f_mapping; 1572 prev = -1; 1573 spin_lock(&swap_lock); 1574 for (type = swap_list.head; type >= 0; type = swap_info[type]->next) { 1575 p = swap_info[type]; 1576 if (p->flags & SWP_WRITEOK) { 1577 if (p->swap_file->f_mapping == mapping) 1578 break; 1579 } 1580 prev = type; 1581 } 1582 if (type < 0) { 1583 err = -EINVAL; 1584 spin_unlock(&swap_lock); 1585 goto out_dput; 1586 } 1587 if (!security_vm_enough_memory(p->pages)) 1588 vm_unacct_memory(p->pages); 1589 else { 1590 err = -ENOMEM; 1591 spin_unlock(&swap_lock); 1592 goto out_dput; 1593 } 1594 if (prev < 0) 1595 swap_list.head = p->next; 1596 else 1597 swap_info[prev]->next = p->next; 1598 if (type == swap_list.next) { 1599 /* just pick something that's safe... */ 1600 swap_list.next = swap_list.head; 1601 } 1602 if (p->prio < 0) { 1603 for (i = p->next; i >= 0; i = swap_info[i]->next) 1604 swap_info[i]->prio = p->prio--; 1605 least_priority++; 1606 } 1607 nr_swap_pages -= p->pages; 1608 total_swap_pages -= p->pages; 1609 p->flags &= ~SWP_WRITEOK; 1610 spin_unlock(&swap_lock); 1611 1612 current->flags |= PF_OOM_ORIGIN; 1613 err = try_to_unuse(type); 1614 current->flags &= ~PF_OOM_ORIGIN; 1615 1616 if (err) { 1617 /* re-insert swap space back into swap_list */ 1618 spin_lock(&swap_lock); 1619 if (p->prio < 0) 1620 p->prio = --least_priority; 1621 prev = -1; 1622 for (i = swap_list.head; i >= 0; i = swap_info[i]->next) { 1623 if (p->prio >= swap_info[i]->prio) 1624 break; 1625 prev = i; 1626 } 1627 p->next = i; 1628 if (prev < 0) 1629 swap_list.head = swap_list.next = type; 1630 else 1631 swap_info[prev]->next = type; 1632 nr_swap_pages += p->pages; 1633 total_swap_pages += p->pages; 1634 p->flags |= SWP_WRITEOK; 1635 spin_unlock(&swap_lock); 1636 goto out_dput; 1637 } 1638 1639 /* wait for any unplug function to finish */ 1640 down_write(&swap_unplug_sem); 1641 up_write(&swap_unplug_sem); 1642 1643 destroy_swap_extents(p); 1644 if (p->flags & SWP_CONTINUED) 1645 free_swap_count_continuations(p); 1646 1647 mutex_lock(&swapon_mutex); 1648 spin_lock(&swap_lock); 1649 drain_mmlist(); 1650 1651 /* wait for anyone still in scan_swap_map */ 1652 p->highest_bit = 0; /* cuts scans short */ 1653 while (p->flags >= SWP_SCANNING) { 1654 spin_unlock(&swap_lock); 1655 schedule_timeout_uninterruptible(1); 1656 spin_lock(&swap_lock); 1657 } 1658 1659 swap_file = p->swap_file; 1660 p->swap_file = NULL; 1661 p->max = 0; 1662 swap_map = p->swap_map; 1663 p->swap_map = NULL; 1664 p->flags = 0; 1665 spin_unlock(&swap_lock); 1666 mutex_unlock(&swapon_mutex); 1667 vfree(swap_map); 1668 /* Destroy swap account informatin */ 1669 swap_cgroup_swapoff(type); 1670 1671 inode = mapping->host; 1672 if (S_ISBLK(inode->i_mode)) { 1673 struct block_device *bdev = I_BDEV(inode); 1674 set_blocksize(bdev, p->old_block_size); 1675 bd_release(bdev); 1676 } else { 1677 mutex_lock(&inode->i_mutex); 1678 inode->i_flags &= ~S_SWAPFILE; 1679 mutex_unlock(&inode->i_mutex); 1680 } 1681 filp_close(swap_file, NULL); 1682 err = 0; 1683 1684 out_dput: 1685 filp_close(victim, NULL); 1686 out: 1687 return err; 1688 } 1689 1690 #ifdef CONFIG_PROC_FS 1691 /* iterator */ 1692 static void *swap_start(struct seq_file *swap, loff_t *pos) 1693 { 1694 struct swap_info_struct *si; 1695 int type; 1696 loff_t l = *pos; 1697 1698 mutex_lock(&swapon_mutex); 1699 1700 if (!l) 1701 return SEQ_START_TOKEN; 1702 1703 for (type = 0; type < nr_swapfiles; type++) { 1704 smp_rmb(); /* read nr_swapfiles before swap_info[type] */ 1705 si = swap_info[type]; 1706 if (!(si->flags & SWP_USED) || !si->swap_map) 1707 continue; 1708 if (!--l) 1709 return si; 1710 } 1711 1712 return NULL; 1713 } 1714 1715 static void *swap_next(struct seq_file *swap, void *v, loff_t *pos) 1716 { 1717 struct swap_info_struct *si = v; 1718 int type; 1719 1720 if (v == SEQ_START_TOKEN) 1721 type = 0; 1722 else 1723 type = si->type + 1; 1724 1725 for (; type < nr_swapfiles; type++) { 1726 smp_rmb(); /* read nr_swapfiles before swap_info[type] */ 1727 si = swap_info[type]; 1728 if (!(si->flags & SWP_USED) || !si->swap_map) 1729 continue; 1730 ++*pos; 1731 return si; 1732 } 1733 1734 return NULL; 1735 } 1736 1737 static void swap_stop(struct seq_file *swap, void *v) 1738 { 1739 mutex_unlock(&swapon_mutex); 1740 } 1741 1742 static int swap_show(struct seq_file *swap, void *v) 1743 { 1744 struct swap_info_struct *si = v; 1745 struct file *file; 1746 int len; 1747 1748 if (si == SEQ_START_TOKEN) { 1749 seq_puts(swap,"Filename\t\t\t\tType\t\tSize\tUsed\tPriority\n"); 1750 return 0; 1751 } 1752 1753 file = si->swap_file; 1754 len = seq_path(swap, &file->f_path, " \t\n\\"); 1755 seq_printf(swap, "%*s%s\t%u\t%u\t%d\n", 1756 len < 40 ? 40 - len : 1, " ", 1757 S_ISBLK(file->f_path.dentry->d_inode->i_mode) ? 1758 "partition" : "file\t", 1759 si->pages << (PAGE_SHIFT - 10), 1760 si->inuse_pages << (PAGE_SHIFT - 10), 1761 si->prio); 1762 return 0; 1763 } 1764 1765 static const struct seq_operations swaps_op = { 1766 .start = swap_start, 1767 .next = swap_next, 1768 .stop = swap_stop, 1769 .show = swap_show 1770 }; 1771 1772 static int swaps_open(struct inode *inode, struct file *file) 1773 { 1774 return seq_open(file, &swaps_op); 1775 } 1776 1777 static const struct file_operations proc_swaps_operations = { 1778 .open = swaps_open, 1779 .read = seq_read, 1780 .llseek = seq_lseek, 1781 .release = seq_release, 1782 }; 1783 1784 static int __init procswaps_init(void) 1785 { 1786 proc_create("swaps", 0, NULL, &proc_swaps_operations); 1787 return 0; 1788 } 1789 __initcall(procswaps_init); 1790 #endif /* CONFIG_PROC_FS */ 1791 1792 #ifdef MAX_SWAPFILES_CHECK 1793 static int __init max_swapfiles_check(void) 1794 { 1795 MAX_SWAPFILES_CHECK(); 1796 return 0; 1797 } 1798 late_initcall(max_swapfiles_check); 1799 #endif 1800 1801 /* 1802 * Written 01/25/92 by Simmule Turner, heavily changed by Linus. 1803 * 1804 * The swapon system call 1805 */ 1806 SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags) 1807 { 1808 struct swap_info_struct *p; 1809 char *name = NULL; 1810 struct block_device *bdev = NULL; 1811 struct file *swap_file = NULL; 1812 struct address_space *mapping; 1813 unsigned int type; 1814 int i, prev; 1815 int error; 1816 union swap_header *swap_header; 1817 unsigned int nr_good_pages; 1818 int nr_extents = 0; 1819 sector_t span; 1820 unsigned long maxpages; 1821 unsigned long swapfilepages; 1822 unsigned char *swap_map = NULL; 1823 struct page *page = NULL; 1824 struct inode *inode = NULL; 1825 int did_down = 0; 1826 1827 if (!capable(CAP_SYS_ADMIN)) 1828 return -EPERM; 1829 1830 p = kzalloc(sizeof(*p), GFP_KERNEL); 1831 if (!p) 1832 return -ENOMEM; 1833 1834 spin_lock(&swap_lock); 1835 for (type = 0; type < nr_swapfiles; type++) { 1836 if (!(swap_info[type]->flags & SWP_USED)) 1837 break; 1838 } 1839 error = -EPERM; 1840 if (type >= MAX_SWAPFILES) { 1841 spin_unlock(&swap_lock); 1842 kfree(p); 1843 goto out; 1844 } 1845 if (type >= nr_swapfiles) { 1846 p->type = type; 1847 swap_info[type] = p; 1848 /* 1849 * Write swap_info[type] before nr_swapfiles, in case a 1850 * racing procfs swap_start() or swap_next() is reading them. 1851 * (We never shrink nr_swapfiles, we never free this entry.) 1852 */ 1853 smp_wmb(); 1854 nr_swapfiles++; 1855 } else { 1856 kfree(p); 1857 p = swap_info[type]; 1858 /* 1859 * Do not memset this entry: a racing procfs swap_next() 1860 * would be relying on p->type to remain valid. 1861 */ 1862 } 1863 INIT_LIST_HEAD(&p->first_swap_extent.list); 1864 p->flags = SWP_USED; 1865 p->next = -1; 1866 spin_unlock(&swap_lock); 1867 1868 name = getname(specialfile); 1869 error = PTR_ERR(name); 1870 if (IS_ERR(name)) { 1871 name = NULL; 1872 goto bad_swap_2; 1873 } 1874 swap_file = filp_open(name, O_RDWR|O_LARGEFILE, 0); 1875 error = PTR_ERR(swap_file); 1876 if (IS_ERR(swap_file)) { 1877 swap_file = NULL; 1878 goto bad_swap_2; 1879 } 1880 1881 p->swap_file = swap_file; 1882 mapping = swap_file->f_mapping; 1883 inode = mapping->host; 1884 1885 error = -EBUSY; 1886 for (i = 0; i < nr_swapfiles; i++) { 1887 struct swap_info_struct *q = swap_info[i]; 1888 1889 if (i == type || !q->swap_file) 1890 continue; 1891 if (mapping == q->swap_file->f_mapping) 1892 goto bad_swap; 1893 } 1894 1895 error = -EINVAL; 1896 if (S_ISBLK(inode->i_mode)) { 1897 bdev = I_BDEV(inode); 1898 error = bd_claim(bdev, sys_swapon); 1899 if (error < 0) { 1900 bdev = NULL; 1901 error = -EINVAL; 1902 goto bad_swap; 1903 } 1904 p->old_block_size = block_size(bdev); 1905 error = set_blocksize(bdev, PAGE_SIZE); 1906 if (error < 0) 1907 goto bad_swap; 1908 p->bdev = bdev; 1909 p->flags |= SWP_BLKDEV; 1910 } else if (S_ISREG(inode->i_mode)) { 1911 p->bdev = inode->i_sb->s_bdev; 1912 mutex_lock(&inode->i_mutex); 1913 did_down = 1; 1914 if (IS_SWAPFILE(inode)) { 1915 error = -EBUSY; 1916 goto bad_swap; 1917 } 1918 } else { 1919 goto bad_swap; 1920 } 1921 1922 swapfilepages = i_size_read(inode) >> PAGE_SHIFT; 1923 1924 /* 1925 * Read the swap header. 1926 */ 1927 if (!mapping->a_ops->readpage) { 1928 error = -EINVAL; 1929 goto bad_swap; 1930 } 1931 page = read_mapping_page(mapping, 0, swap_file); 1932 if (IS_ERR(page)) { 1933 error = PTR_ERR(page); 1934 goto bad_swap; 1935 } 1936 swap_header = kmap(page); 1937 1938 if (memcmp("SWAPSPACE2", swap_header->magic.magic, 10)) { 1939 printk(KERN_ERR "Unable to find swap-space signature\n"); 1940 error = -EINVAL; 1941 goto bad_swap; 1942 } 1943 1944 /* swap partition endianess hack... */ 1945 if (swab32(swap_header->info.version) == 1) { 1946 swab32s(&swap_header->info.version); 1947 swab32s(&swap_header->info.last_page); 1948 swab32s(&swap_header->info.nr_badpages); 1949 for (i = 0; i < swap_header->info.nr_badpages; i++) 1950 swab32s(&swap_header->info.badpages[i]); 1951 } 1952 /* Check the swap header's sub-version */ 1953 if (swap_header->info.version != 1) { 1954 printk(KERN_WARNING 1955 "Unable to handle swap header version %d\n", 1956 swap_header->info.version); 1957 error = -EINVAL; 1958 goto bad_swap; 1959 } 1960 1961 p->lowest_bit = 1; 1962 p->cluster_next = 1; 1963 p->cluster_nr = 0; 1964 1965 /* 1966 * Find out how many pages are allowed for a single swap 1967 * device. There are two limiting factors: 1) the number of 1968 * bits for the swap offset in the swp_entry_t type and 1969 * 2) the number of bits in the a swap pte as defined by 1970 * the different architectures. In order to find the 1971 * largest possible bit mask a swap entry with swap type 0 1972 * and swap offset ~0UL is created, encoded to a swap pte, 1973 * decoded to a swp_entry_t again and finally the swap 1974 * offset is extracted. This will mask all the bits from 1975 * the initial ~0UL mask that can't be encoded in either 1976 * the swp_entry_t or the architecture definition of a 1977 * swap pte. 1978 */ 1979 maxpages = swp_offset(pte_to_swp_entry( 1980 swp_entry_to_pte(swp_entry(0, ~0UL)))) + 1; 1981 if (maxpages > swap_header->info.last_page) { 1982 maxpages = swap_header->info.last_page + 1; 1983 /* p->max is an unsigned int: don't overflow it */ 1984 if ((unsigned int)maxpages == 0) 1985 maxpages = UINT_MAX; 1986 } 1987 p->highest_bit = maxpages - 1; 1988 1989 error = -EINVAL; 1990 if (!maxpages) 1991 goto bad_swap; 1992 if (swapfilepages && maxpages > swapfilepages) { 1993 printk(KERN_WARNING 1994 "Swap area shorter than signature indicates\n"); 1995 goto bad_swap; 1996 } 1997 if (swap_header->info.nr_badpages && S_ISREG(inode->i_mode)) 1998 goto bad_swap; 1999 if (swap_header->info.nr_badpages > MAX_SWAP_BADPAGES) 2000 goto bad_swap; 2001 2002 /* OK, set up the swap map and apply the bad block list */ 2003 swap_map = vmalloc(maxpages); 2004 if (!swap_map) { 2005 error = -ENOMEM; 2006 goto bad_swap; 2007 } 2008 2009 memset(swap_map, 0, maxpages); 2010 nr_good_pages = maxpages - 1; /* omit header page */ 2011 2012 for (i = 0; i < swap_header->info.nr_badpages; i++) { 2013 unsigned int page_nr = swap_header->info.badpages[i]; 2014 if (page_nr == 0 || page_nr > swap_header->info.last_page) { 2015 error = -EINVAL; 2016 goto bad_swap; 2017 } 2018 if (page_nr < maxpages) { 2019 swap_map[page_nr] = SWAP_MAP_BAD; 2020 nr_good_pages--; 2021 } 2022 } 2023 2024 error = swap_cgroup_swapon(type, maxpages); 2025 if (error) 2026 goto bad_swap; 2027 2028 if (nr_good_pages) { 2029 swap_map[0] = SWAP_MAP_BAD; 2030 p->max = maxpages; 2031 p->pages = nr_good_pages; 2032 nr_extents = setup_swap_extents(p, &span); 2033 if (nr_extents < 0) { 2034 error = nr_extents; 2035 goto bad_swap; 2036 } 2037 nr_good_pages = p->pages; 2038 } 2039 if (!nr_good_pages) { 2040 printk(KERN_WARNING "Empty swap-file\n"); 2041 error = -EINVAL; 2042 goto bad_swap; 2043 } 2044 2045 if (p->bdev) { 2046 if (blk_queue_nonrot(bdev_get_queue(p->bdev))) { 2047 p->flags |= SWP_SOLIDSTATE; 2048 p->cluster_next = 1 + (random32() % p->highest_bit); 2049 } 2050 if (discard_swap(p) == 0 && (swap_flags & SWAP_FLAG_DISCARD)) 2051 p->flags |= SWP_DISCARDABLE; 2052 } 2053 2054 mutex_lock(&swapon_mutex); 2055 spin_lock(&swap_lock); 2056 if (swap_flags & SWAP_FLAG_PREFER) 2057 p->prio = 2058 (swap_flags & SWAP_FLAG_PRIO_MASK) >> SWAP_FLAG_PRIO_SHIFT; 2059 else 2060 p->prio = --least_priority; 2061 p->swap_map = swap_map; 2062 p->flags |= SWP_WRITEOK; 2063 nr_swap_pages += nr_good_pages; 2064 total_swap_pages += nr_good_pages; 2065 2066 printk(KERN_INFO "Adding %uk swap on %s. " 2067 "Priority:%d extents:%d across:%lluk %s%s\n", 2068 nr_good_pages<<(PAGE_SHIFT-10), name, p->prio, 2069 nr_extents, (unsigned long long)span<<(PAGE_SHIFT-10), 2070 (p->flags & SWP_SOLIDSTATE) ? "SS" : "", 2071 (p->flags & SWP_DISCARDABLE) ? "D" : ""); 2072 2073 /* insert swap space into swap_list: */ 2074 prev = -1; 2075 for (i = swap_list.head; i >= 0; i = swap_info[i]->next) { 2076 if (p->prio >= swap_info[i]->prio) 2077 break; 2078 prev = i; 2079 } 2080 p->next = i; 2081 if (prev < 0) 2082 swap_list.head = swap_list.next = type; 2083 else 2084 swap_info[prev]->next = type; 2085 spin_unlock(&swap_lock); 2086 mutex_unlock(&swapon_mutex); 2087 error = 0; 2088 goto out; 2089 bad_swap: 2090 if (bdev) { 2091 set_blocksize(bdev, p->old_block_size); 2092 bd_release(bdev); 2093 } 2094 destroy_swap_extents(p); 2095 swap_cgroup_swapoff(type); 2096 bad_swap_2: 2097 spin_lock(&swap_lock); 2098 p->swap_file = NULL; 2099 p->flags = 0; 2100 spin_unlock(&swap_lock); 2101 vfree(swap_map); 2102 if (swap_file) 2103 filp_close(swap_file, NULL); 2104 out: 2105 if (page && !IS_ERR(page)) { 2106 kunmap(page); 2107 page_cache_release(page); 2108 } 2109 if (name) 2110 putname(name); 2111 if (did_down) { 2112 if (!error) 2113 inode->i_flags |= S_SWAPFILE; 2114 mutex_unlock(&inode->i_mutex); 2115 } 2116 return error; 2117 } 2118 2119 void si_swapinfo(struct sysinfo *val) 2120 { 2121 unsigned int type; 2122 unsigned long nr_to_be_unused = 0; 2123 2124 spin_lock(&swap_lock); 2125 for (type = 0; type < nr_swapfiles; type++) { 2126 struct swap_info_struct *si = swap_info[type]; 2127 2128 if ((si->flags & SWP_USED) && !(si->flags & SWP_WRITEOK)) 2129 nr_to_be_unused += si->inuse_pages; 2130 } 2131 val->freeswap = nr_swap_pages + nr_to_be_unused; 2132 val->totalswap = total_swap_pages + nr_to_be_unused; 2133 spin_unlock(&swap_lock); 2134 } 2135 2136 /* 2137 * Verify that a swap entry is valid and increment its swap map count. 2138 * 2139 * Returns error code in following case. 2140 * - success -> 0 2141 * - swp_entry is invalid -> EINVAL 2142 * - swp_entry is migration entry -> EINVAL 2143 * - swap-cache reference is requested but there is already one. -> EEXIST 2144 * - swap-cache reference is requested but the entry is not used. -> ENOENT 2145 * - swap-mapped reference requested but needs continued swap count. -> ENOMEM 2146 */ 2147 static int __swap_duplicate(swp_entry_t entry, unsigned char usage) 2148 { 2149 struct swap_info_struct *p; 2150 unsigned long offset, type; 2151 unsigned char count; 2152 unsigned char has_cache; 2153 int err = -EINVAL; 2154 2155 if (non_swap_entry(entry)) 2156 goto out; 2157 2158 type = swp_type(entry); 2159 if (type >= nr_swapfiles) 2160 goto bad_file; 2161 p = swap_info[type]; 2162 offset = swp_offset(entry); 2163 2164 spin_lock(&swap_lock); 2165 if (unlikely(offset >= p->max)) 2166 goto unlock_out; 2167 2168 count = p->swap_map[offset]; 2169 has_cache = count & SWAP_HAS_CACHE; 2170 count &= ~SWAP_HAS_CACHE; 2171 err = 0; 2172 2173 if (usage == SWAP_HAS_CACHE) { 2174 2175 /* set SWAP_HAS_CACHE if there is no cache and entry is used */ 2176 if (!has_cache && count) 2177 has_cache = SWAP_HAS_CACHE; 2178 else if (has_cache) /* someone else added cache */ 2179 err = -EEXIST; 2180 else /* no users remaining */ 2181 err = -ENOENT; 2182 2183 } else if (count || has_cache) { 2184 2185 if ((count & ~COUNT_CONTINUED) < SWAP_MAP_MAX) 2186 count += usage; 2187 else if ((count & ~COUNT_CONTINUED) > SWAP_MAP_MAX) 2188 err = -EINVAL; 2189 else if (swap_count_continued(p, offset, count)) 2190 count = COUNT_CONTINUED; 2191 else 2192 err = -ENOMEM; 2193 } else 2194 err = -ENOENT; /* unused swap entry */ 2195 2196 p->swap_map[offset] = count | has_cache; 2197 2198 unlock_out: 2199 spin_unlock(&swap_lock); 2200 out: 2201 return err; 2202 2203 bad_file: 2204 printk(KERN_ERR "swap_dup: %s%08lx\n", Bad_file, entry.val); 2205 goto out; 2206 } 2207 2208 /* 2209 * Help swapoff by noting that swap entry belongs to shmem/tmpfs 2210 * (in which case its reference count is never incremented). 2211 */ 2212 void swap_shmem_alloc(swp_entry_t entry) 2213 { 2214 __swap_duplicate(entry, SWAP_MAP_SHMEM); 2215 } 2216 2217 /* 2218 * Increase reference count of swap entry by 1. 2219 * Returns 0 for success, or -ENOMEM if a swap_count_continuation is required 2220 * but could not be atomically allocated. Returns 0, just as if it succeeded, 2221 * if __swap_duplicate() fails for another reason (-EINVAL or -ENOENT), which 2222 * might occur if a page table entry has got corrupted. 2223 */ 2224 int swap_duplicate(swp_entry_t entry) 2225 { 2226 int err = 0; 2227 2228 while (!err && __swap_duplicate(entry, 1) == -ENOMEM) 2229 err = add_swap_count_continuation(entry, GFP_ATOMIC); 2230 return err; 2231 } 2232 2233 /* 2234 * @entry: swap entry for which we allocate swap cache. 2235 * 2236 * Called when allocating swap cache for existing swap entry, 2237 * This can return error codes. Returns 0 at success. 2238 * -EBUSY means there is a swap cache. 2239 * Note: return code is different from swap_duplicate(). 2240 */ 2241 int swapcache_prepare(swp_entry_t entry) 2242 { 2243 return __swap_duplicate(entry, SWAP_HAS_CACHE); 2244 } 2245 2246 /* 2247 * swap_lock prevents swap_map being freed. Don't grab an extra 2248 * reference on the swaphandle, it doesn't matter if it becomes unused. 2249 */ 2250 int valid_swaphandles(swp_entry_t entry, unsigned long *offset) 2251 { 2252 struct swap_info_struct *si; 2253 int our_page_cluster = page_cluster; 2254 pgoff_t target, toff; 2255 pgoff_t base, end; 2256 int nr_pages = 0; 2257 2258 if (!our_page_cluster) /* no readahead */ 2259 return 0; 2260 2261 si = swap_info[swp_type(entry)]; 2262 target = swp_offset(entry); 2263 base = (target >> our_page_cluster) << our_page_cluster; 2264 end = base + (1 << our_page_cluster); 2265 if (!base) /* first page is swap header */ 2266 base++; 2267 2268 spin_lock(&swap_lock); 2269 if (end > si->max) /* don't go beyond end of map */ 2270 end = si->max; 2271 2272 /* Count contiguous allocated slots above our target */ 2273 for (toff = target; ++toff < end; nr_pages++) { 2274 /* Don't read in free or bad pages */ 2275 if (!si->swap_map[toff]) 2276 break; 2277 if (swap_count(si->swap_map[toff]) == SWAP_MAP_BAD) 2278 break; 2279 } 2280 /* Count contiguous allocated slots below our target */ 2281 for (toff = target; --toff >= base; nr_pages++) { 2282 /* Don't read in free or bad pages */ 2283 if (!si->swap_map[toff]) 2284 break; 2285 if (swap_count(si->swap_map[toff]) == SWAP_MAP_BAD) 2286 break; 2287 } 2288 spin_unlock(&swap_lock); 2289 2290 /* 2291 * Indicate starting offset, and return number of pages to get: 2292 * if only 1, say 0, since there's then no readahead to be done. 2293 */ 2294 *offset = ++toff; 2295 return nr_pages? ++nr_pages: 0; 2296 } 2297 2298 /* 2299 * add_swap_count_continuation - called when a swap count is duplicated 2300 * beyond SWAP_MAP_MAX, it allocates a new page and links that to the entry's 2301 * page of the original vmalloc'ed swap_map, to hold the continuation count 2302 * (for that entry and for its neighbouring PAGE_SIZE swap entries). Called 2303 * again when count is duplicated beyond SWAP_MAP_MAX * SWAP_CONT_MAX, etc. 2304 * 2305 * These continuation pages are seldom referenced: the common paths all work 2306 * on the original swap_map, only referring to a continuation page when the 2307 * low "digit" of a count is incremented or decremented through SWAP_MAP_MAX. 2308 * 2309 * add_swap_count_continuation(, GFP_ATOMIC) can be called while holding 2310 * page table locks; if it fails, add_swap_count_continuation(, GFP_KERNEL) 2311 * can be called after dropping locks. 2312 */ 2313 int add_swap_count_continuation(swp_entry_t entry, gfp_t gfp_mask) 2314 { 2315 struct swap_info_struct *si; 2316 struct page *head; 2317 struct page *page; 2318 struct page *list_page; 2319 pgoff_t offset; 2320 unsigned char count; 2321 2322 /* 2323 * When debugging, it's easier to use __GFP_ZERO here; but it's better 2324 * for latency not to zero a page while GFP_ATOMIC and holding locks. 2325 */ 2326 page = alloc_page(gfp_mask | __GFP_HIGHMEM); 2327 2328 si = swap_info_get(entry); 2329 if (!si) { 2330 /* 2331 * An acceptable race has occurred since the failing 2332 * __swap_duplicate(): the swap entry has been freed, 2333 * perhaps even the whole swap_map cleared for swapoff. 2334 */ 2335 goto outer; 2336 } 2337 2338 offset = swp_offset(entry); 2339 count = si->swap_map[offset] & ~SWAP_HAS_CACHE; 2340 2341 if ((count & ~COUNT_CONTINUED) != SWAP_MAP_MAX) { 2342 /* 2343 * The higher the swap count, the more likely it is that tasks 2344 * will race to add swap count continuation: we need to avoid 2345 * over-provisioning. 2346 */ 2347 goto out; 2348 } 2349 2350 if (!page) { 2351 spin_unlock(&swap_lock); 2352 return -ENOMEM; 2353 } 2354 2355 /* 2356 * We are fortunate that although vmalloc_to_page uses pte_offset_map, 2357 * no architecture is using highmem pages for kernel pagetables: so it 2358 * will not corrupt the GFP_ATOMIC caller's atomic pagetable kmaps. 2359 */ 2360 head = vmalloc_to_page(si->swap_map + offset); 2361 offset &= ~PAGE_MASK; 2362 2363 /* 2364 * Page allocation does not initialize the page's lru field, 2365 * but it does always reset its private field. 2366 */ 2367 if (!page_private(head)) { 2368 BUG_ON(count & COUNT_CONTINUED); 2369 INIT_LIST_HEAD(&head->lru); 2370 set_page_private(head, SWP_CONTINUED); 2371 si->flags |= SWP_CONTINUED; 2372 } 2373 2374 list_for_each_entry(list_page, &head->lru, lru) { 2375 unsigned char *map; 2376 2377 /* 2378 * If the previous map said no continuation, but we've found 2379 * a continuation page, free our allocation and use this one. 2380 */ 2381 if (!(count & COUNT_CONTINUED)) 2382 goto out; 2383 2384 map = kmap_atomic(list_page, KM_USER0) + offset; 2385 count = *map; 2386 kunmap_atomic(map, KM_USER0); 2387 2388 /* 2389 * If this continuation count now has some space in it, 2390 * free our allocation and use this one. 2391 */ 2392 if ((count & ~COUNT_CONTINUED) != SWAP_CONT_MAX) 2393 goto out; 2394 } 2395 2396 list_add_tail(&page->lru, &head->lru); 2397 page = NULL; /* now it's attached, don't free it */ 2398 out: 2399 spin_unlock(&swap_lock); 2400 outer: 2401 if (page) 2402 __free_page(page); 2403 return 0; 2404 } 2405 2406 /* 2407 * swap_count_continued - when the original swap_map count is incremented 2408 * from SWAP_MAP_MAX, check if there is already a continuation page to carry 2409 * into, carry if so, or else fail until a new continuation page is allocated; 2410 * when the original swap_map count is decremented from 0 with continuation, 2411 * borrow from the continuation and report whether it still holds more. 2412 * Called while __swap_duplicate() or swap_entry_free() holds swap_lock. 2413 */ 2414 static bool swap_count_continued(struct swap_info_struct *si, 2415 pgoff_t offset, unsigned char count) 2416 { 2417 struct page *head; 2418 struct page *page; 2419 unsigned char *map; 2420 2421 head = vmalloc_to_page(si->swap_map + offset); 2422 if (page_private(head) != SWP_CONTINUED) { 2423 BUG_ON(count & COUNT_CONTINUED); 2424 return false; /* need to add count continuation */ 2425 } 2426 2427 offset &= ~PAGE_MASK; 2428 page = list_entry(head->lru.next, struct page, lru); 2429 map = kmap_atomic(page, KM_USER0) + offset; 2430 2431 if (count == SWAP_MAP_MAX) /* initial increment from swap_map */ 2432 goto init_map; /* jump over SWAP_CONT_MAX checks */ 2433 2434 if (count == (SWAP_MAP_MAX | COUNT_CONTINUED)) { /* incrementing */ 2435 /* 2436 * Think of how you add 1 to 999 2437 */ 2438 while (*map == (SWAP_CONT_MAX | COUNT_CONTINUED)) { 2439 kunmap_atomic(map, KM_USER0); 2440 page = list_entry(page->lru.next, struct page, lru); 2441 BUG_ON(page == head); 2442 map = kmap_atomic(page, KM_USER0) + offset; 2443 } 2444 if (*map == SWAP_CONT_MAX) { 2445 kunmap_atomic(map, KM_USER0); 2446 page = list_entry(page->lru.next, struct page, lru); 2447 if (page == head) 2448 return false; /* add count continuation */ 2449 map = kmap_atomic(page, KM_USER0) + offset; 2450 init_map: *map = 0; /* we didn't zero the page */ 2451 } 2452 *map += 1; 2453 kunmap_atomic(map, KM_USER0); 2454 page = list_entry(page->lru.prev, struct page, lru); 2455 while (page != head) { 2456 map = kmap_atomic(page, KM_USER0) + offset; 2457 *map = COUNT_CONTINUED; 2458 kunmap_atomic(map, KM_USER0); 2459 page = list_entry(page->lru.prev, struct page, lru); 2460 } 2461 return true; /* incremented */ 2462 2463 } else { /* decrementing */ 2464 /* 2465 * Think of how you subtract 1 from 1000 2466 */ 2467 BUG_ON(count != COUNT_CONTINUED); 2468 while (*map == COUNT_CONTINUED) { 2469 kunmap_atomic(map, KM_USER0); 2470 page = list_entry(page->lru.next, struct page, lru); 2471 BUG_ON(page == head); 2472 map = kmap_atomic(page, KM_USER0) + offset; 2473 } 2474 BUG_ON(*map == 0); 2475 *map -= 1; 2476 if (*map == 0) 2477 count = 0; 2478 kunmap_atomic(map, KM_USER0); 2479 page = list_entry(page->lru.prev, struct page, lru); 2480 while (page != head) { 2481 map = kmap_atomic(page, KM_USER0) + offset; 2482 *map = SWAP_CONT_MAX | count; 2483 count = COUNT_CONTINUED; 2484 kunmap_atomic(map, KM_USER0); 2485 page = list_entry(page->lru.prev, struct page, lru); 2486 } 2487 return count == COUNT_CONTINUED; 2488 } 2489 } 2490 2491 /* 2492 * free_swap_count_continuations - swapoff free all the continuation pages 2493 * appended to the swap_map, after swap_map is quiesced, before vfree'ing it. 2494 */ 2495 static void free_swap_count_continuations(struct swap_info_struct *si) 2496 { 2497 pgoff_t offset; 2498 2499 for (offset = 0; offset < si->max; offset += PAGE_SIZE) { 2500 struct page *head; 2501 head = vmalloc_to_page(si->swap_map + offset); 2502 if (page_private(head)) { 2503 struct list_head *this, *next; 2504 list_for_each_safe(this, next, &head->lru) { 2505 struct page *page; 2506 page = list_entry(this, struct page, lru); 2507 list_del(this); 2508 __free_page(page); 2509 } 2510 } 2511 } 2512 } 2513