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/shmem_fs.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/ksm.h> 25 #include <linux/rmap.h> 26 #include <linux/security.h> 27 #include <linux/backing-dev.h> 28 #include <linux/mutex.h> 29 #include <linux/capability.h> 30 #include <linux/syscalls.h> 31 #include <linux/memcontrol.h> 32 #include <linux/poll.h> 33 #include <linux/oom.h> 34 #include <linux/frontswap.h> 35 #include <linux/swapfile.h> 36 #include <linux/export.h> 37 38 #include <asm/pgtable.h> 39 #include <asm/tlbflush.h> 40 #include <linux/swapops.h> 41 #include <linux/swap_cgroup.h> 42 43 static bool swap_count_continued(struct swap_info_struct *, pgoff_t, 44 unsigned char); 45 static void free_swap_count_continuations(struct swap_info_struct *); 46 static sector_t map_swap_entry(swp_entry_t, struct block_device**); 47 48 DEFINE_SPINLOCK(swap_lock); 49 static unsigned int nr_swapfiles; 50 atomic_long_t nr_swap_pages; 51 /* 52 * Some modules use swappable objects and may try to swap them out under 53 * memory pressure (via the shrinker). Before doing so, they may wish to 54 * check to see if any swap space is available. 55 */ 56 EXPORT_SYMBOL_GPL(nr_swap_pages); 57 /* protected with swap_lock. reading in vm_swap_full() doesn't need lock */ 58 long total_swap_pages; 59 static int least_priority; 60 61 static const char Bad_file[] = "Bad swap file entry "; 62 static const char Unused_file[] = "Unused swap file entry "; 63 static const char Bad_offset[] = "Bad swap offset entry "; 64 static const char Unused_offset[] = "Unused swap offset entry "; 65 66 /* 67 * all active swap_info_structs 68 * protected with swap_lock, and ordered by priority. 69 */ 70 PLIST_HEAD(swap_active_head); 71 72 /* 73 * all available (active, not full) swap_info_structs 74 * protected with swap_avail_lock, ordered by priority. 75 * This is used by get_swap_page() instead of swap_active_head 76 * because swap_active_head includes all swap_info_structs, 77 * but get_swap_page() doesn't need to look at full ones. 78 * This uses its own lock instead of swap_lock because when a 79 * swap_info_struct changes between not-full/full, it needs to 80 * add/remove itself to/from this list, but the swap_info_struct->lock 81 * is held and the locking order requires swap_lock to be taken 82 * before any swap_info_struct->lock. 83 */ 84 static PLIST_HEAD(swap_avail_head); 85 static DEFINE_SPINLOCK(swap_avail_lock); 86 87 struct swap_info_struct *swap_info[MAX_SWAPFILES]; 88 89 static DEFINE_MUTEX(swapon_mutex); 90 91 static DECLARE_WAIT_QUEUE_HEAD(proc_poll_wait); 92 /* Activity counter to indicate that a swapon or swapoff has occurred */ 93 static atomic_t proc_poll_event = ATOMIC_INIT(0); 94 95 static inline unsigned char swap_count(unsigned char ent) 96 { 97 return ent & ~SWAP_HAS_CACHE; /* may include SWAP_HAS_CONT flag */ 98 } 99 100 /* returns 1 if swap entry is freed */ 101 static int 102 __try_to_reclaim_swap(struct swap_info_struct *si, unsigned long offset) 103 { 104 swp_entry_t entry = swp_entry(si->type, offset); 105 struct page *page; 106 int ret = 0; 107 108 page = find_get_page(swap_address_space(entry), swp_offset(entry)); 109 if (!page) 110 return 0; 111 /* 112 * This function is called from scan_swap_map() and it's called 113 * by vmscan.c at reclaiming pages. So, we hold a lock on a page, here. 114 * We have to use trylock for avoiding deadlock. This is a special 115 * case and you should use try_to_free_swap() with explicit lock_page() 116 * in usual operations. 117 */ 118 if (trylock_page(page)) { 119 ret = try_to_free_swap(page); 120 unlock_page(page); 121 } 122 put_page(page); 123 return ret; 124 } 125 126 /* 127 * swapon tell device that all the old swap contents can be discarded, 128 * to allow the swap device to optimize its wear-levelling. 129 */ 130 static int discard_swap(struct swap_info_struct *si) 131 { 132 struct swap_extent *se; 133 sector_t start_block; 134 sector_t nr_blocks; 135 int err = 0; 136 137 /* Do not discard the swap header page! */ 138 se = &si->first_swap_extent; 139 start_block = (se->start_block + 1) << (PAGE_SHIFT - 9); 140 nr_blocks = ((sector_t)se->nr_pages - 1) << (PAGE_SHIFT - 9); 141 if (nr_blocks) { 142 err = blkdev_issue_discard(si->bdev, start_block, 143 nr_blocks, GFP_KERNEL, 0); 144 if (err) 145 return err; 146 cond_resched(); 147 } 148 149 list_for_each_entry(se, &si->first_swap_extent.list, list) { 150 start_block = se->start_block << (PAGE_SHIFT - 9); 151 nr_blocks = (sector_t)se->nr_pages << (PAGE_SHIFT - 9); 152 153 err = blkdev_issue_discard(si->bdev, start_block, 154 nr_blocks, GFP_KERNEL, 0); 155 if (err) 156 break; 157 158 cond_resched(); 159 } 160 return err; /* That will often be -EOPNOTSUPP */ 161 } 162 163 /* 164 * swap allocation tell device that a cluster of swap can now be discarded, 165 * to allow the swap device to optimize its wear-levelling. 166 */ 167 static void discard_swap_cluster(struct swap_info_struct *si, 168 pgoff_t start_page, pgoff_t nr_pages) 169 { 170 struct swap_extent *se = si->curr_swap_extent; 171 int found_extent = 0; 172 173 while (nr_pages) { 174 if (se->start_page <= start_page && 175 start_page < se->start_page + se->nr_pages) { 176 pgoff_t offset = start_page - se->start_page; 177 sector_t start_block = se->start_block + offset; 178 sector_t nr_blocks = se->nr_pages - offset; 179 180 if (nr_blocks > nr_pages) 181 nr_blocks = nr_pages; 182 start_page += nr_blocks; 183 nr_pages -= nr_blocks; 184 185 if (!found_extent++) 186 si->curr_swap_extent = se; 187 188 start_block <<= PAGE_SHIFT - 9; 189 nr_blocks <<= PAGE_SHIFT - 9; 190 if (blkdev_issue_discard(si->bdev, start_block, 191 nr_blocks, GFP_NOIO, 0)) 192 break; 193 } 194 195 se = list_next_entry(se, list); 196 } 197 } 198 199 #define SWAPFILE_CLUSTER 256 200 #define LATENCY_LIMIT 256 201 202 static inline void cluster_set_flag(struct swap_cluster_info *info, 203 unsigned int flag) 204 { 205 info->flags = flag; 206 } 207 208 static inline unsigned int cluster_count(struct swap_cluster_info *info) 209 { 210 return info->data; 211 } 212 213 static inline void cluster_set_count(struct swap_cluster_info *info, 214 unsigned int c) 215 { 216 info->data = c; 217 } 218 219 static inline void cluster_set_count_flag(struct swap_cluster_info *info, 220 unsigned int c, unsigned int f) 221 { 222 info->flags = f; 223 info->data = c; 224 } 225 226 static inline unsigned int cluster_next(struct swap_cluster_info *info) 227 { 228 return info->data; 229 } 230 231 static inline void cluster_set_next(struct swap_cluster_info *info, 232 unsigned int n) 233 { 234 info->data = n; 235 } 236 237 static inline void cluster_set_next_flag(struct swap_cluster_info *info, 238 unsigned int n, unsigned int f) 239 { 240 info->flags = f; 241 info->data = n; 242 } 243 244 static inline bool cluster_is_free(struct swap_cluster_info *info) 245 { 246 return info->flags & CLUSTER_FLAG_FREE; 247 } 248 249 static inline bool cluster_is_null(struct swap_cluster_info *info) 250 { 251 return info->flags & CLUSTER_FLAG_NEXT_NULL; 252 } 253 254 static inline void cluster_set_null(struct swap_cluster_info *info) 255 { 256 info->flags = CLUSTER_FLAG_NEXT_NULL; 257 info->data = 0; 258 } 259 260 static inline bool cluster_list_empty(struct swap_cluster_list *list) 261 { 262 return cluster_is_null(&list->head); 263 } 264 265 static inline unsigned int cluster_list_first(struct swap_cluster_list *list) 266 { 267 return cluster_next(&list->head); 268 } 269 270 static void cluster_list_init(struct swap_cluster_list *list) 271 { 272 cluster_set_null(&list->head); 273 cluster_set_null(&list->tail); 274 } 275 276 static void cluster_list_add_tail(struct swap_cluster_list *list, 277 struct swap_cluster_info *ci, 278 unsigned int idx) 279 { 280 if (cluster_list_empty(list)) { 281 cluster_set_next_flag(&list->head, idx, 0); 282 cluster_set_next_flag(&list->tail, idx, 0); 283 } else { 284 unsigned int tail = cluster_next(&list->tail); 285 286 cluster_set_next(&ci[tail], idx); 287 cluster_set_next_flag(&list->tail, idx, 0); 288 } 289 } 290 291 static unsigned int cluster_list_del_first(struct swap_cluster_list *list, 292 struct swap_cluster_info *ci) 293 { 294 unsigned int idx; 295 296 idx = cluster_next(&list->head); 297 if (cluster_next(&list->tail) == idx) { 298 cluster_set_null(&list->head); 299 cluster_set_null(&list->tail); 300 } else 301 cluster_set_next_flag(&list->head, 302 cluster_next(&ci[idx]), 0); 303 304 return idx; 305 } 306 307 /* Add a cluster to discard list and schedule it to do discard */ 308 static void swap_cluster_schedule_discard(struct swap_info_struct *si, 309 unsigned int idx) 310 { 311 /* 312 * If scan_swap_map() can't find a free cluster, it will check 313 * si->swap_map directly. To make sure the discarding cluster isn't 314 * taken by scan_swap_map(), mark the swap entries bad (occupied). It 315 * will be cleared after discard 316 */ 317 memset(si->swap_map + idx * SWAPFILE_CLUSTER, 318 SWAP_MAP_BAD, SWAPFILE_CLUSTER); 319 320 cluster_list_add_tail(&si->discard_clusters, si->cluster_info, idx); 321 322 schedule_work(&si->discard_work); 323 } 324 325 /* 326 * Doing discard actually. After a cluster discard is finished, the cluster 327 * will be added to free cluster list. caller should hold si->lock. 328 */ 329 static void swap_do_scheduled_discard(struct swap_info_struct *si) 330 { 331 struct swap_cluster_info *info; 332 unsigned int idx; 333 334 info = si->cluster_info; 335 336 while (!cluster_list_empty(&si->discard_clusters)) { 337 idx = cluster_list_del_first(&si->discard_clusters, info); 338 spin_unlock(&si->lock); 339 340 discard_swap_cluster(si, idx * SWAPFILE_CLUSTER, 341 SWAPFILE_CLUSTER); 342 343 spin_lock(&si->lock); 344 cluster_set_flag(&info[idx], CLUSTER_FLAG_FREE); 345 cluster_list_add_tail(&si->free_clusters, info, idx); 346 memset(si->swap_map + idx * SWAPFILE_CLUSTER, 347 0, SWAPFILE_CLUSTER); 348 } 349 } 350 351 static void swap_discard_work(struct work_struct *work) 352 { 353 struct swap_info_struct *si; 354 355 si = container_of(work, struct swap_info_struct, discard_work); 356 357 spin_lock(&si->lock); 358 swap_do_scheduled_discard(si); 359 spin_unlock(&si->lock); 360 } 361 362 /* 363 * The cluster corresponding to page_nr will be used. The cluster will be 364 * removed from free cluster list and its usage counter will be increased. 365 */ 366 static void inc_cluster_info_page(struct swap_info_struct *p, 367 struct swap_cluster_info *cluster_info, unsigned long page_nr) 368 { 369 unsigned long idx = page_nr / SWAPFILE_CLUSTER; 370 371 if (!cluster_info) 372 return; 373 if (cluster_is_free(&cluster_info[idx])) { 374 VM_BUG_ON(cluster_list_first(&p->free_clusters) != idx); 375 cluster_list_del_first(&p->free_clusters, cluster_info); 376 cluster_set_count_flag(&cluster_info[idx], 0, 0); 377 } 378 379 VM_BUG_ON(cluster_count(&cluster_info[idx]) >= SWAPFILE_CLUSTER); 380 cluster_set_count(&cluster_info[idx], 381 cluster_count(&cluster_info[idx]) + 1); 382 } 383 384 /* 385 * The cluster corresponding to page_nr decreases one usage. If the usage 386 * counter becomes 0, which means no page in the cluster is in using, we can 387 * optionally discard the cluster and add it to free cluster list. 388 */ 389 static void dec_cluster_info_page(struct swap_info_struct *p, 390 struct swap_cluster_info *cluster_info, unsigned long page_nr) 391 { 392 unsigned long idx = page_nr / SWAPFILE_CLUSTER; 393 394 if (!cluster_info) 395 return; 396 397 VM_BUG_ON(cluster_count(&cluster_info[idx]) == 0); 398 cluster_set_count(&cluster_info[idx], 399 cluster_count(&cluster_info[idx]) - 1); 400 401 if (cluster_count(&cluster_info[idx]) == 0) { 402 /* 403 * If the swap is discardable, prepare discard the cluster 404 * instead of free it immediately. The cluster will be freed 405 * after discard. 406 */ 407 if ((p->flags & (SWP_WRITEOK | SWP_PAGE_DISCARD)) == 408 (SWP_WRITEOK | SWP_PAGE_DISCARD)) { 409 swap_cluster_schedule_discard(p, idx); 410 return; 411 } 412 413 cluster_set_flag(&cluster_info[idx], CLUSTER_FLAG_FREE); 414 cluster_list_add_tail(&p->free_clusters, cluster_info, idx); 415 } 416 } 417 418 /* 419 * It's possible scan_swap_map() uses a free cluster in the middle of free 420 * cluster list. Avoiding such abuse to avoid list corruption. 421 */ 422 static bool 423 scan_swap_map_ssd_cluster_conflict(struct swap_info_struct *si, 424 unsigned long offset) 425 { 426 struct percpu_cluster *percpu_cluster; 427 bool conflict; 428 429 offset /= SWAPFILE_CLUSTER; 430 conflict = !cluster_list_empty(&si->free_clusters) && 431 offset != cluster_list_first(&si->free_clusters) && 432 cluster_is_free(&si->cluster_info[offset]); 433 434 if (!conflict) 435 return false; 436 437 percpu_cluster = this_cpu_ptr(si->percpu_cluster); 438 cluster_set_null(&percpu_cluster->index); 439 return true; 440 } 441 442 /* 443 * Try to get a swap entry from current cpu's swap entry pool (a cluster). This 444 * might involve allocating a new cluster for current CPU too. 445 */ 446 static void scan_swap_map_try_ssd_cluster(struct swap_info_struct *si, 447 unsigned long *offset, unsigned long *scan_base) 448 { 449 struct percpu_cluster *cluster; 450 bool found_free; 451 unsigned long tmp; 452 453 new_cluster: 454 cluster = this_cpu_ptr(si->percpu_cluster); 455 if (cluster_is_null(&cluster->index)) { 456 if (!cluster_list_empty(&si->free_clusters)) { 457 cluster->index = si->free_clusters.head; 458 cluster->next = cluster_next(&cluster->index) * 459 SWAPFILE_CLUSTER; 460 } else if (!cluster_list_empty(&si->discard_clusters)) { 461 /* 462 * we don't have free cluster but have some clusters in 463 * discarding, do discard now and reclaim them 464 */ 465 swap_do_scheduled_discard(si); 466 *scan_base = *offset = si->cluster_next; 467 goto new_cluster; 468 } else 469 return; 470 } 471 472 found_free = false; 473 474 /* 475 * Other CPUs can use our cluster if they can't find a free cluster, 476 * check if there is still free entry in the cluster 477 */ 478 tmp = cluster->next; 479 while (tmp < si->max && tmp < (cluster_next(&cluster->index) + 1) * 480 SWAPFILE_CLUSTER) { 481 if (!si->swap_map[tmp]) { 482 found_free = true; 483 break; 484 } 485 tmp++; 486 } 487 if (!found_free) { 488 cluster_set_null(&cluster->index); 489 goto new_cluster; 490 } 491 cluster->next = tmp + 1; 492 *offset = tmp; 493 *scan_base = tmp; 494 } 495 496 static unsigned long scan_swap_map(struct swap_info_struct *si, 497 unsigned char usage) 498 { 499 unsigned long offset; 500 unsigned long scan_base; 501 unsigned long last_in_cluster = 0; 502 int latency_ration = LATENCY_LIMIT; 503 504 /* 505 * We try to cluster swap pages by allocating them sequentially 506 * in swap. Once we've allocated SWAPFILE_CLUSTER pages this 507 * way, however, we resort to first-free allocation, starting 508 * a new cluster. This prevents us from scattering swap pages 509 * all over the entire swap partition, so that we reduce 510 * overall disk seek times between swap pages. -- sct 511 * But we do now try to find an empty cluster. -Andrea 512 * And we let swap pages go all over an SSD partition. Hugh 513 */ 514 515 si->flags += SWP_SCANNING; 516 scan_base = offset = si->cluster_next; 517 518 /* SSD algorithm */ 519 if (si->cluster_info) { 520 scan_swap_map_try_ssd_cluster(si, &offset, &scan_base); 521 goto checks; 522 } 523 524 if (unlikely(!si->cluster_nr--)) { 525 if (si->pages - si->inuse_pages < SWAPFILE_CLUSTER) { 526 si->cluster_nr = SWAPFILE_CLUSTER - 1; 527 goto checks; 528 } 529 530 spin_unlock(&si->lock); 531 532 /* 533 * If seek is expensive, start searching for new cluster from 534 * start of partition, to minimize the span of allocated swap. 535 * If seek is cheap, that is the SWP_SOLIDSTATE si->cluster_info 536 * case, just handled by scan_swap_map_try_ssd_cluster() above. 537 */ 538 scan_base = offset = si->lowest_bit; 539 last_in_cluster = offset + SWAPFILE_CLUSTER - 1; 540 541 /* Locate the first empty (unaligned) cluster */ 542 for (; last_in_cluster <= si->highest_bit; offset++) { 543 if (si->swap_map[offset]) 544 last_in_cluster = offset + SWAPFILE_CLUSTER; 545 else if (offset == last_in_cluster) { 546 spin_lock(&si->lock); 547 offset -= SWAPFILE_CLUSTER - 1; 548 si->cluster_next = offset; 549 si->cluster_nr = SWAPFILE_CLUSTER - 1; 550 goto checks; 551 } 552 if (unlikely(--latency_ration < 0)) { 553 cond_resched(); 554 latency_ration = LATENCY_LIMIT; 555 } 556 } 557 558 offset = scan_base; 559 spin_lock(&si->lock); 560 si->cluster_nr = SWAPFILE_CLUSTER - 1; 561 } 562 563 checks: 564 if (si->cluster_info) { 565 while (scan_swap_map_ssd_cluster_conflict(si, offset)) 566 scan_swap_map_try_ssd_cluster(si, &offset, &scan_base); 567 } 568 if (!(si->flags & SWP_WRITEOK)) 569 goto no_page; 570 if (!si->highest_bit) 571 goto no_page; 572 if (offset > si->highest_bit) 573 scan_base = offset = si->lowest_bit; 574 575 /* reuse swap entry of cache-only swap if not busy. */ 576 if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) { 577 int swap_was_freed; 578 spin_unlock(&si->lock); 579 swap_was_freed = __try_to_reclaim_swap(si, offset); 580 spin_lock(&si->lock); 581 /* entry was freed successfully, try to use this again */ 582 if (swap_was_freed) 583 goto checks; 584 goto scan; /* check next one */ 585 } 586 587 if (si->swap_map[offset]) 588 goto scan; 589 590 if (offset == si->lowest_bit) 591 si->lowest_bit++; 592 if (offset == si->highest_bit) 593 si->highest_bit--; 594 si->inuse_pages++; 595 if (si->inuse_pages == si->pages) { 596 si->lowest_bit = si->max; 597 si->highest_bit = 0; 598 spin_lock(&swap_avail_lock); 599 plist_del(&si->avail_list, &swap_avail_head); 600 spin_unlock(&swap_avail_lock); 601 } 602 si->swap_map[offset] = usage; 603 inc_cluster_info_page(si, si->cluster_info, offset); 604 si->cluster_next = offset + 1; 605 si->flags -= SWP_SCANNING; 606 607 return offset; 608 609 scan: 610 spin_unlock(&si->lock); 611 while (++offset <= si->highest_bit) { 612 if (!si->swap_map[offset]) { 613 spin_lock(&si->lock); 614 goto checks; 615 } 616 if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) { 617 spin_lock(&si->lock); 618 goto checks; 619 } 620 if (unlikely(--latency_ration < 0)) { 621 cond_resched(); 622 latency_ration = LATENCY_LIMIT; 623 } 624 } 625 offset = si->lowest_bit; 626 while (offset < scan_base) { 627 if (!si->swap_map[offset]) { 628 spin_lock(&si->lock); 629 goto checks; 630 } 631 if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) { 632 spin_lock(&si->lock); 633 goto checks; 634 } 635 if (unlikely(--latency_ration < 0)) { 636 cond_resched(); 637 latency_ration = LATENCY_LIMIT; 638 } 639 offset++; 640 } 641 spin_lock(&si->lock); 642 643 no_page: 644 si->flags -= SWP_SCANNING; 645 return 0; 646 } 647 648 swp_entry_t get_swap_page(void) 649 { 650 struct swap_info_struct *si, *next; 651 pgoff_t offset; 652 653 if (atomic_long_read(&nr_swap_pages) <= 0) 654 goto noswap; 655 atomic_long_dec(&nr_swap_pages); 656 657 spin_lock(&swap_avail_lock); 658 659 start_over: 660 plist_for_each_entry_safe(si, next, &swap_avail_head, avail_list) { 661 /* requeue si to after same-priority siblings */ 662 plist_requeue(&si->avail_list, &swap_avail_head); 663 spin_unlock(&swap_avail_lock); 664 spin_lock(&si->lock); 665 if (!si->highest_bit || !(si->flags & SWP_WRITEOK)) { 666 spin_lock(&swap_avail_lock); 667 if (plist_node_empty(&si->avail_list)) { 668 spin_unlock(&si->lock); 669 goto nextsi; 670 } 671 WARN(!si->highest_bit, 672 "swap_info %d in list but !highest_bit\n", 673 si->type); 674 WARN(!(si->flags & SWP_WRITEOK), 675 "swap_info %d in list but !SWP_WRITEOK\n", 676 si->type); 677 plist_del(&si->avail_list, &swap_avail_head); 678 spin_unlock(&si->lock); 679 goto nextsi; 680 } 681 682 /* This is called for allocating swap entry for cache */ 683 offset = scan_swap_map(si, SWAP_HAS_CACHE); 684 spin_unlock(&si->lock); 685 if (offset) 686 return swp_entry(si->type, offset); 687 pr_debug("scan_swap_map of si %d failed to find offset\n", 688 si->type); 689 spin_lock(&swap_avail_lock); 690 nextsi: 691 /* 692 * if we got here, it's likely that si was almost full before, 693 * and since scan_swap_map() can drop the si->lock, multiple 694 * callers probably all tried to get a page from the same si 695 * and it filled up before we could get one; or, the si filled 696 * up between us dropping swap_avail_lock and taking si->lock. 697 * Since we dropped the swap_avail_lock, the swap_avail_head 698 * list may have been modified; so if next is still in the 699 * swap_avail_head list then try it, otherwise start over. 700 */ 701 if (plist_node_empty(&next->avail_list)) 702 goto start_over; 703 } 704 705 spin_unlock(&swap_avail_lock); 706 707 atomic_long_inc(&nr_swap_pages); 708 noswap: 709 return (swp_entry_t) {0}; 710 } 711 712 /* The only caller of this function is now suspend routine */ 713 swp_entry_t get_swap_page_of_type(int type) 714 { 715 struct swap_info_struct *si; 716 pgoff_t offset; 717 718 si = swap_info[type]; 719 spin_lock(&si->lock); 720 if (si && (si->flags & SWP_WRITEOK)) { 721 atomic_long_dec(&nr_swap_pages); 722 /* This is called for allocating swap entry, not cache */ 723 offset = scan_swap_map(si, 1); 724 if (offset) { 725 spin_unlock(&si->lock); 726 return swp_entry(type, offset); 727 } 728 atomic_long_inc(&nr_swap_pages); 729 } 730 spin_unlock(&si->lock); 731 return (swp_entry_t) {0}; 732 } 733 734 static struct swap_info_struct *swap_info_get(swp_entry_t entry) 735 { 736 struct swap_info_struct *p; 737 unsigned long offset, type; 738 739 if (!entry.val) 740 goto out; 741 type = swp_type(entry); 742 if (type >= nr_swapfiles) 743 goto bad_nofile; 744 p = swap_info[type]; 745 if (!(p->flags & SWP_USED)) 746 goto bad_device; 747 offset = swp_offset(entry); 748 if (offset >= p->max) 749 goto bad_offset; 750 if (!p->swap_map[offset]) 751 goto bad_free; 752 spin_lock(&p->lock); 753 return p; 754 755 bad_free: 756 pr_err("swap_free: %s%08lx\n", Unused_offset, entry.val); 757 goto out; 758 bad_offset: 759 pr_err("swap_free: %s%08lx\n", Bad_offset, entry.val); 760 goto out; 761 bad_device: 762 pr_err("swap_free: %s%08lx\n", Unused_file, entry.val); 763 goto out; 764 bad_nofile: 765 pr_err("swap_free: %s%08lx\n", Bad_file, entry.val); 766 out: 767 return NULL; 768 } 769 770 static unsigned char swap_entry_free(struct swap_info_struct *p, 771 swp_entry_t entry, unsigned char usage) 772 { 773 unsigned long offset = swp_offset(entry); 774 unsigned char count; 775 unsigned char has_cache; 776 777 count = p->swap_map[offset]; 778 has_cache = count & SWAP_HAS_CACHE; 779 count &= ~SWAP_HAS_CACHE; 780 781 if (usage == SWAP_HAS_CACHE) { 782 VM_BUG_ON(!has_cache); 783 has_cache = 0; 784 } else if (count == SWAP_MAP_SHMEM) { 785 /* 786 * Or we could insist on shmem.c using a special 787 * swap_shmem_free() and free_shmem_swap_and_cache()... 788 */ 789 count = 0; 790 } else if ((count & ~COUNT_CONTINUED) <= SWAP_MAP_MAX) { 791 if (count == COUNT_CONTINUED) { 792 if (swap_count_continued(p, offset, count)) 793 count = SWAP_MAP_MAX | COUNT_CONTINUED; 794 else 795 count = SWAP_MAP_MAX; 796 } else 797 count--; 798 } 799 800 usage = count | has_cache; 801 p->swap_map[offset] = usage; 802 803 /* free if no reference */ 804 if (!usage) { 805 mem_cgroup_uncharge_swap(entry); 806 dec_cluster_info_page(p, p->cluster_info, offset); 807 if (offset < p->lowest_bit) 808 p->lowest_bit = offset; 809 if (offset > p->highest_bit) { 810 bool was_full = !p->highest_bit; 811 p->highest_bit = offset; 812 if (was_full && (p->flags & SWP_WRITEOK)) { 813 spin_lock(&swap_avail_lock); 814 WARN_ON(!plist_node_empty(&p->avail_list)); 815 if (plist_node_empty(&p->avail_list)) 816 plist_add(&p->avail_list, 817 &swap_avail_head); 818 spin_unlock(&swap_avail_lock); 819 } 820 } 821 atomic_long_inc(&nr_swap_pages); 822 p->inuse_pages--; 823 frontswap_invalidate_page(p->type, offset); 824 if (p->flags & SWP_BLKDEV) { 825 struct gendisk *disk = p->bdev->bd_disk; 826 if (disk->fops->swap_slot_free_notify) 827 disk->fops->swap_slot_free_notify(p->bdev, 828 offset); 829 } 830 } 831 832 return usage; 833 } 834 835 /* 836 * Caller has made sure that the swap device corresponding to entry 837 * is still around or has not been recycled. 838 */ 839 void swap_free(swp_entry_t entry) 840 { 841 struct swap_info_struct *p; 842 843 p = swap_info_get(entry); 844 if (p) { 845 swap_entry_free(p, entry, 1); 846 spin_unlock(&p->lock); 847 } 848 } 849 850 /* 851 * Called after dropping swapcache to decrease refcnt to swap entries. 852 */ 853 void swapcache_free(swp_entry_t entry) 854 { 855 struct swap_info_struct *p; 856 857 p = swap_info_get(entry); 858 if (p) { 859 swap_entry_free(p, entry, SWAP_HAS_CACHE); 860 spin_unlock(&p->lock); 861 } 862 } 863 864 /* 865 * How many references to page are currently swapped out? 866 * This does not give an exact answer when swap count is continued, 867 * but does include the high COUNT_CONTINUED flag to allow for that. 868 */ 869 int page_swapcount(struct page *page) 870 { 871 int count = 0; 872 struct swap_info_struct *p; 873 swp_entry_t entry; 874 875 entry.val = page_private(page); 876 p = swap_info_get(entry); 877 if (p) { 878 count = swap_count(p->swap_map[swp_offset(entry)]); 879 spin_unlock(&p->lock); 880 } 881 return count; 882 } 883 884 /* 885 * How many references to @entry are currently swapped out? 886 * This considers COUNT_CONTINUED so it returns exact answer. 887 */ 888 int swp_swapcount(swp_entry_t entry) 889 { 890 int count, tmp_count, n; 891 struct swap_info_struct *p; 892 struct page *page; 893 pgoff_t offset; 894 unsigned char *map; 895 896 p = swap_info_get(entry); 897 if (!p) 898 return 0; 899 900 count = swap_count(p->swap_map[swp_offset(entry)]); 901 if (!(count & COUNT_CONTINUED)) 902 goto out; 903 904 count &= ~COUNT_CONTINUED; 905 n = SWAP_MAP_MAX + 1; 906 907 offset = swp_offset(entry); 908 page = vmalloc_to_page(p->swap_map + offset); 909 offset &= ~PAGE_MASK; 910 VM_BUG_ON(page_private(page) != SWP_CONTINUED); 911 912 do { 913 page = list_next_entry(page, lru); 914 map = kmap_atomic(page); 915 tmp_count = map[offset]; 916 kunmap_atomic(map); 917 918 count += (tmp_count & ~COUNT_CONTINUED) * n; 919 n *= (SWAP_CONT_MAX + 1); 920 } while (tmp_count & COUNT_CONTINUED); 921 out: 922 spin_unlock(&p->lock); 923 return count; 924 } 925 926 /* 927 * We can write to an anon page without COW if there are no other references 928 * to it. And as a side-effect, free up its swap: because the old content 929 * on disk will never be read, and seeking back there to write new content 930 * later would only waste time away from clustering. 931 * 932 * NOTE: total_mapcount should not be relied upon by the caller if 933 * reuse_swap_page() returns false, but it may be always overwritten 934 * (see the other implementation for CONFIG_SWAP=n). 935 */ 936 bool reuse_swap_page(struct page *page, int *total_mapcount) 937 { 938 int count; 939 940 VM_BUG_ON_PAGE(!PageLocked(page), page); 941 if (unlikely(PageKsm(page))) 942 return false; 943 count = page_trans_huge_mapcount(page, total_mapcount); 944 if (count <= 1 && PageSwapCache(page)) { 945 count += page_swapcount(page); 946 if (count != 1) 947 goto out; 948 if (!PageWriteback(page)) { 949 delete_from_swap_cache(page); 950 SetPageDirty(page); 951 } else { 952 swp_entry_t entry; 953 struct swap_info_struct *p; 954 955 entry.val = page_private(page); 956 p = swap_info_get(entry); 957 if (p->flags & SWP_STABLE_WRITES) { 958 spin_unlock(&p->lock); 959 return false; 960 } 961 spin_unlock(&p->lock); 962 } 963 } 964 out: 965 return count <= 1; 966 } 967 968 /* 969 * If swap is getting full, or if there are no more mappings of this page, 970 * then try_to_free_swap is called to free its swap space. 971 */ 972 int try_to_free_swap(struct page *page) 973 { 974 VM_BUG_ON_PAGE(!PageLocked(page), page); 975 976 if (!PageSwapCache(page)) 977 return 0; 978 if (PageWriteback(page)) 979 return 0; 980 if (page_swapcount(page)) 981 return 0; 982 983 /* 984 * Once hibernation has begun to create its image of memory, 985 * there's a danger that one of the calls to try_to_free_swap() 986 * - most probably a call from __try_to_reclaim_swap() while 987 * hibernation is allocating its own swap pages for the image, 988 * but conceivably even a call from memory reclaim - will free 989 * the swap from a page which has already been recorded in the 990 * image as a clean swapcache page, and then reuse its swap for 991 * another page of the image. On waking from hibernation, the 992 * original page might be freed under memory pressure, then 993 * later read back in from swap, now with the wrong data. 994 * 995 * Hibernation suspends storage while it is writing the image 996 * to disk so check that here. 997 */ 998 if (pm_suspended_storage()) 999 return 0; 1000 1001 delete_from_swap_cache(page); 1002 SetPageDirty(page); 1003 return 1; 1004 } 1005 1006 /* 1007 * Free the swap entry like above, but also try to 1008 * free the page cache entry if it is the last user. 1009 */ 1010 int free_swap_and_cache(swp_entry_t entry) 1011 { 1012 struct swap_info_struct *p; 1013 struct page *page = NULL; 1014 1015 if (non_swap_entry(entry)) 1016 return 1; 1017 1018 p = swap_info_get(entry); 1019 if (p) { 1020 if (swap_entry_free(p, entry, 1) == SWAP_HAS_CACHE) { 1021 page = find_get_page(swap_address_space(entry), 1022 swp_offset(entry)); 1023 if (page && !trylock_page(page)) { 1024 put_page(page); 1025 page = NULL; 1026 } 1027 } 1028 spin_unlock(&p->lock); 1029 } 1030 if (page) { 1031 /* 1032 * Not mapped elsewhere, or swap space full? Free it! 1033 * Also recheck PageSwapCache now page is locked (above). 1034 */ 1035 if (PageSwapCache(page) && !PageWriteback(page) && 1036 (!page_mapped(page) || mem_cgroup_swap_full(page))) { 1037 delete_from_swap_cache(page); 1038 SetPageDirty(page); 1039 } 1040 unlock_page(page); 1041 put_page(page); 1042 } 1043 return p != NULL; 1044 } 1045 1046 #ifdef CONFIG_HIBERNATION 1047 /* 1048 * Find the swap type that corresponds to given device (if any). 1049 * 1050 * @offset - number of the PAGE_SIZE-sized block of the device, starting 1051 * from 0, in which the swap header is expected to be located. 1052 * 1053 * This is needed for the suspend to disk (aka swsusp). 1054 */ 1055 int swap_type_of(dev_t device, sector_t offset, struct block_device **bdev_p) 1056 { 1057 struct block_device *bdev = NULL; 1058 int type; 1059 1060 if (device) 1061 bdev = bdget(device); 1062 1063 spin_lock(&swap_lock); 1064 for (type = 0; type < nr_swapfiles; type++) { 1065 struct swap_info_struct *sis = swap_info[type]; 1066 1067 if (!(sis->flags & SWP_WRITEOK)) 1068 continue; 1069 1070 if (!bdev) { 1071 if (bdev_p) 1072 *bdev_p = bdgrab(sis->bdev); 1073 1074 spin_unlock(&swap_lock); 1075 return type; 1076 } 1077 if (bdev == sis->bdev) { 1078 struct swap_extent *se = &sis->first_swap_extent; 1079 1080 if (se->start_block == offset) { 1081 if (bdev_p) 1082 *bdev_p = bdgrab(sis->bdev); 1083 1084 spin_unlock(&swap_lock); 1085 bdput(bdev); 1086 return type; 1087 } 1088 } 1089 } 1090 spin_unlock(&swap_lock); 1091 if (bdev) 1092 bdput(bdev); 1093 1094 return -ENODEV; 1095 } 1096 1097 /* 1098 * Get the (PAGE_SIZE) block corresponding to given offset on the swapdev 1099 * corresponding to given index in swap_info (swap type). 1100 */ 1101 sector_t swapdev_block(int type, pgoff_t offset) 1102 { 1103 struct block_device *bdev; 1104 1105 if ((unsigned int)type >= nr_swapfiles) 1106 return 0; 1107 if (!(swap_info[type]->flags & SWP_WRITEOK)) 1108 return 0; 1109 return map_swap_entry(swp_entry(type, offset), &bdev); 1110 } 1111 1112 /* 1113 * Return either the total number of swap pages of given type, or the number 1114 * of free pages of that type (depending on @free) 1115 * 1116 * This is needed for software suspend 1117 */ 1118 unsigned int count_swap_pages(int type, int free) 1119 { 1120 unsigned int n = 0; 1121 1122 spin_lock(&swap_lock); 1123 if ((unsigned int)type < nr_swapfiles) { 1124 struct swap_info_struct *sis = swap_info[type]; 1125 1126 spin_lock(&sis->lock); 1127 if (sis->flags & SWP_WRITEOK) { 1128 n = sis->pages; 1129 if (free) 1130 n -= sis->inuse_pages; 1131 } 1132 spin_unlock(&sis->lock); 1133 } 1134 spin_unlock(&swap_lock); 1135 return n; 1136 } 1137 #endif /* CONFIG_HIBERNATION */ 1138 1139 static inline int pte_same_as_swp(pte_t pte, pte_t swp_pte) 1140 { 1141 return pte_same(pte_swp_clear_soft_dirty(pte), swp_pte); 1142 } 1143 1144 /* 1145 * No need to decide whether this PTE shares the swap entry with others, 1146 * just let do_wp_page work it out if a write is requested later - to 1147 * force COW, vm_page_prot omits write permission from any private vma. 1148 */ 1149 static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd, 1150 unsigned long addr, swp_entry_t entry, struct page *page) 1151 { 1152 struct page *swapcache; 1153 struct mem_cgroup *memcg; 1154 spinlock_t *ptl; 1155 pte_t *pte; 1156 int ret = 1; 1157 1158 swapcache = page; 1159 page = ksm_might_need_to_copy(page, vma, addr); 1160 if (unlikely(!page)) 1161 return -ENOMEM; 1162 1163 if (mem_cgroup_try_charge(page, vma->vm_mm, GFP_KERNEL, 1164 &memcg, false)) { 1165 ret = -ENOMEM; 1166 goto out_nolock; 1167 } 1168 1169 pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl); 1170 if (unlikely(!pte_same_as_swp(*pte, swp_entry_to_pte(entry)))) { 1171 mem_cgroup_cancel_charge(page, memcg, false); 1172 ret = 0; 1173 goto out; 1174 } 1175 1176 dec_mm_counter(vma->vm_mm, MM_SWAPENTS); 1177 inc_mm_counter(vma->vm_mm, MM_ANONPAGES); 1178 get_page(page); 1179 set_pte_at(vma->vm_mm, addr, pte, 1180 pte_mkold(mk_pte(page, vma->vm_page_prot))); 1181 if (page == swapcache) { 1182 page_add_anon_rmap(page, vma, addr, false); 1183 mem_cgroup_commit_charge(page, memcg, true, false); 1184 } else { /* ksm created a completely new copy */ 1185 page_add_new_anon_rmap(page, vma, addr, false); 1186 mem_cgroup_commit_charge(page, memcg, false, false); 1187 lru_cache_add_active_or_unevictable(page, vma); 1188 } 1189 swap_free(entry); 1190 /* 1191 * Move the page to the active list so it is not 1192 * immediately swapped out again after swapon. 1193 */ 1194 activate_page(page); 1195 out: 1196 pte_unmap_unlock(pte, ptl); 1197 out_nolock: 1198 if (page != swapcache) { 1199 unlock_page(page); 1200 put_page(page); 1201 } 1202 return ret; 1203 } 1204 1205 static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd, 1206 unsigned long addr, unsigned long end, 1207 swp_entry_t entry, struct page *page) 1208 { 1209 pte_t swp_pte = swp_entry_to_pte(entry); 1210 pte_t *pte; 1211 int ret = 0; 1212 1213 /* 1214 * We don't actually need pte lock while scanning for swp_pte: since 1215 * we hold page lock and mmap_sem, swp_pte cannot be inserted into the 1216 * page table while we're scanning; though it could get zapped, and on 1217 * some architectures (e.g. x86_32 with PAE) we might catch a glimpse 1218 * of unmatched parts which look like swp_pte, so unuse_pte must 1219 * recheck under pte lock. Scanning without pte lock lets it be 1220 * preemptable whenever CONFIG_PREEMPT but not CONFIG_HIGHPTE. 1221 */ 1222 pte = pte_offset_map(pmd, addr); 1223 do { 1224 /* 1225 * swapoff spends a _lot_ of time in this loop! 1226 * Test inline before going to call unuse_pte. 1227 */ 1228 if (unlikely(pte_same_as_swp(*pte, swp_pte))) { 1229 pte_unmap(pte); 1230 ret = unuse_pte(vma, pmd, addr, entry, page); 1231 if (ret) 1232 goto out; 1233 pte = pte_offset_map(pmd, addr); 1234 } 1235 } while (pte++, addr += PAGE_SIZE, addr != end); 1236 pte_unmap(pte - 1); 1237 out: 1238 return ret; 1239 } 1240 1241 static inline int unuse_pmd_range(struct vm_area_struct *vma, pud_t *pud, 1242 unsigned long addr, unsigned long end, 1243 swp_entry_t entry, struct page *page) 1244 { 1245 pmd_t *pmd; 1246 unsigned long next; 1247 int ret; 1248 1249 pmd = pmd_offset(pud, addr); 1250 do { 1251 cond_resched(); 1252 next = pmd_addr_end(addr, end); 1253 if (pmd_none_or_trans_huge_or_clear_bad(pmd)) 1254 continue; 1255 ret = unuse_pte_range(vma, pmd, addr, next, entry, page); 1256 if (ret) 1257 return ret; 1258 } while (pmd++, addr = next, addr != end); 1259 return 0; 1260 } 1261 1262 static inline int unuse_pud_range(struct vm_area_struct *vma, pgd_t *pgd, 1263 unsigned long addr, unsigned long end, 1264 swp_entry_t entry, struct page *page) 1265 { 1266 pud_t *pud; 1267 unsigned long next; 1268 int ret; 1269 1270 pud = pud_offset(pgd, addr); 1271 do { 1272 next = pud_addr_end(addr, end); 1273 if (pud_none_or_clear_bad(pud)) 1274 continue; 1275 ret = unuse_pmd_range(vma, pud, addr, next, entry, page); 1276 if (ret) 1277 return ret; 1278 } while (pud++, addr = next, addr != end); 1279 return 0; 1280 } 1281 1282 static int unuse_vma(struct vm_area_struct *vma, 1283 swp_entry_t entry, struct page *page) 1284 { 1285 pgd_t *pgd; 1286 unsigned long addr, end, next; 1287 int ret; 1288 1289 if (page_anon_vma(page)) { 1290 addr = page_address_in_vma(page, vma); 1291 if (addr == -EFAULT) 1292 return 0; 1293 else 1294 end = addr + PAGE_SIZE; 1295 } else { 1296 addr = vma->vm_start; 1297 end = vma->vm_end; 1298 } 1299 1300 pgd = pgd_offset(vma->vm_mm, addr); 1301 do { 1302 next = pgd_addr_end(addr, end); 1303 if (pgd_none_or_clear_bad(pgd)) 1304 continue; 1305 ret = unuse_pud_range(vma, pgd, addr, next, entry, page); 1306 if (ret) 1307 return ret; 1308 } while (pgd++, addr = next, addr != end); 1309 return 0; 1310 } 1311 1312 static int unuse_mm(struct mm_struct *mm, 1313 swp_entry_t entry, struct page *page) 1314 { 1315 struct vm_area_struct *vma; 1316 int ret = 0; 1317 1318 if (!down_read_trylock(&mm->mmap_sem)) { 1319 /* 1320 * Activate page so shrink_inactive_list is unlikely to unmap 1321 * its ptes while lock is dropped, so swapoff can make progress. 1322 */ 1323 activate_page(page); 1324 unlock_page(page); 1325 down_read(&mm->mmap_sem); 1326 lock_page(page); 1327 } 1328 for (vma = mm->mmap; vma; vma = vma->vm_next) { 1329 if (vma->anon_vma && (ret = unuse_vma(vma, entry, page))) 1330 break; 1331 cond_resched(); 1332 } 1333 up_read(&mm->mmap_sem); 1334 return (ret < 0)? ret: 0; 1335 } 1336 1337 /* 1338 * Scan swap_map (or frontswap_map if frontswap parameter is true) 1339 * from current position to next entry still in use. 1340 * Recycle to start on reaching the end, returning 0 when empty. 1341 */ 1342 static unsigned int find_next_to_unuse(struct swap_info_struct *si, 1343 unsigned int prev, bool frontswap) 1344 { 1345 unsigned int max = si->max; 1346 unsigned int i = prev; 1347 unsigned char count; 1348 1349 /* 1350 * No need for swap_lock here: we're just looking 1351 * for whether an entry is in use, not modifying it; false 1352 * hits are okay, and sys_swapoff() has already prevented new 1353 * allocations from this area (while holding swap_lock). 1354 */ 1355 for (;;) { 1356 if (++i >= max) { 1357 if (!prev) { 1358 i = 0; 1359 break; 1360 } 1361 /* 1362 * No entries in use at top of swap_map, 1363 * loop back to start and recheck there. 1364 */ 1365 max = prev + 1; 1366 prev = 0; 1367 i = 1; 1368 } 1369 count = READ_ONCE(si->swap_map[i]); 1370 if (count && swap_count(count) != SWAP_MAP_BAD) 1371 if (!frontswap || frontswap_test(si, i)) 1372 break; 1373 if ((i % LATENCY_LIMIT) == 0) 1374 cond_resched(); 1375 } 1376 return i; 1377 } 1378 1379 /* 1380 * We completely avoid races by reading each swap page in advance, 1381 * and then search for the process using it. All the necessary 1382 * page table adjustments can then be made atomically. 1383 * 1384 * if the boolean frontswap is true, only unuse pages_to_unuse pages; 1385 * pages_to_unuse==0 means all pages; ignored if frontswap is false 1386 */ 1387 int try_to_unuse(unsigned int type, bool frontswap, 1388 unsigned long pages_to_unuse) 1389 { 1390 struct swap_info_struct *si = swap_info[type]; 1391 struct mm_struct *start_mm; 1392 volatile unsigned char *swap_map; /* swap_map is accessed without 1393 * locking. Mark it as volatile 1394 * to prevent compiler doing 1395 * something odd. 1396 */ 1397 unsigned char swcount; 1398 struct page *page; 1399 swp_entry_t entry; 1400 unsigned int i = 0; 1401 int retval = 0; 1402 1403 /* 1404 * When searching mms for an entry, a good strategy is to 1405 * start at the first mm we freed the previous entry from 1406 * (though actually we don't notice whether we or coincidence 1407 * freed the entry). Initialize this start_mm with a hold. 1408 * 1409 * A simpler strategy would be to start at the last mm we 1410 * freed the previous entry from; but that would take less 1411 * advantage of mmlist ordering, which clusters forked mms 1412 * together, child after parent. If we race with dup_mmap(), we 1413 * prefer to resolve parent before child, lest we miss entries 1414 * duplicated after we scanned child: using last mm would invert 1415 * that. 1416 */ 1417 start_mm = &init_mm; 1418 atomic_inc(&init_mm.mm_users); 1419 1420 /* 1421 * Keep on scanning until all entries have gone. Usually, 1422 * one pass through swap_map is enough, but not necessarily: 1423 * there are races when an instance of an entry might be missed. 1424 */ 1425 while ((i = find_next_to_unuse(si, i, frontswap)) != 0) { 1426 if (signal_pending(current)) { 1427 retval = -EINTR; 1428 break; 1429 } 1430 1431 /* 1432 * Get a page for the entry, using the existing swap 1433 * cache page if there is one. Otherwise, get a clean 1434 * page and read the swap into it. 1435 */ 1436 swap_map = &si->swap_map[i]; 1437 entry = swp_entry(type, i); 1438 page = read_swap_cache_async(entry, 1439 GFP_HIGHUSER_MOVABLE, NULL, 0); 1440 if (!page) { 1441 /* 1442 * Either swap_duplicate() failed because entry 1443 * has been freed independently, and will not be 1444 * reused since sys_swapoff() already disabled 1445 * allocation from here, or alloc_page() failed. 1446 */ 1447 swcount = *swap_map; 1448 /* 1449 * We don't hold lock here, so the swap entry could be 1450 * SWAP_MAP_BAD (when the cluster is discarding). 1451 * Instead of fail out, We can just skip the swap 1452 * entry because swapoff will wait for discarding 1453 * finish anyway. 1454 */ 1455 if (!swcount || swcount == SWAP_MAP_BAD) 1456 continue; 1457 retval = -ENOMEM; 1458 break; 1459 } 1460 1461 /* 1462 * Don't hold on to start_mm if it looks like exiting. 1463 */ 1464 if (atomic_read(&start_mm->mm_users) == 1) { 1465 mmput(start_mm); 1466 start_mm = &init_mm; 1467 atomic_inc(&init_mm.mm_users); 1468 } 1469 1470 /* 1471 * Wait for and lock page. When do_swap_page races with 1472 * try_to_unuse, do_swap_page can handle the fault much 1473 * faster than try_to_unuse can locate the entry. This 1474 * apparently redundant "wait_on_page_locked" lets try_to_unuse 1475 * defer to do_swap_page in such a case - in some tests, 1476 * do_swap_page and try_to_unuse repeatedly compete. 1477 */ 1478 wait_on_page_locked(page); 1479 wait_on_page_writeback(page); 1480 lock_page(page); 1481 wait_on_page_writeback(page); 1482 1483 /* 1484 * Remove all references to entry. 1485 */ 1486 swcount = *swap_map; 1487 if (swap_count(swcount) == SWAP_MAP_SHMEM) { 1488 retval = shmem_unuse(entry, page); 1489 /* page has already been unlocked and released */ 1490 if (retval < 0) 1491 break; 1492 continue; 1493 } 1494 if (swap_count(swcount) && start_mm != &init_mm) 1495 retval = unuse_mm(start_mm, entry, page); 1496 1497 if (swap_count(*swap_map)) { 1498 int set_start_mm = (*swap_map >= swcount); 1499 struct list_head *p = &start_mm->mmlist; 1500 struct mm_struct *new_start_mm = start_mm; 1501 struct mm_struct *prev_mm = start_mm; 1502 struct mm_struct *mm; 1503 1504 atomic_inc(&new_start_mm->mm_users); 1505 atomic_inc(&prev_mm->mm_users); 1506 spin_lock(&mmlist_lock); 1507 while (swap_count(*swap_map) && !retval && 1508 (p = p->next) != &start_mm->mmlist) { 1509 mm = list_entry(p, struct mm_struct, mmlist); 1510 if (!atomic_inc_not_zero(&mm->mm_users)) 1511 continue; 1512 spin_unlock(&mmlist_lock); 1513 mmput(prev_mm); 1514 prev_mm = mm; 1515 1516 cond_resched(); 1517 1518 swcount = *swap_map; 1519 if (!swap_count(swcount)) /* any usage ? */ 1520 ; 1521 else if (mm == &init_mm) 1522 set_start_mm = 1; 1523 else 1524 retval = unuse_mm(mm, entry, page); 1525 1526 if (set_start_mm && *swap_map < swcount) { 1527 mmput(new_start_mm); 1528 atomic_inc(&mm->mm_users); 1529 new_start_mm = mm; 1530 set_start_mm = 0; 1531 } 1532 spin_lock(&mmlist_lock); 1533 } 1534 spin_unlock(&mmlist_lock); 1535 mmput(prev_mm); 1536 mmput(start_mm); 1537 start_mm = new_start_mm; 1538 } 1539 if (retval) { 1540 unlock_page(page); 1541 put_page(page); 1542 break; 1543 } 1544 1545 /* 1546 * If a reference remains (rare), we would like to leave 1547 * the page in the swap cache; but try_to_unmap could 1548 * then re-duplicate the entry once we drop page lock, 1549 * so we might loop indefinitely; also, that page could 1550 * not be swapped out to other storage meanwhile. So: 1551 * delete from cache even if there's another reference, 1552 * after ensuring that the data has been saved to disk - 1553 * since if the reference remains (rarer), it will be 1554 * read from disk into another page. Splitting into two 1555 * pages would be incorrect if swap supported "shared 1556 * private" pages, but they are handled by tmpfs files. 1557 * 1558 * Given how unuse_vma() targets one particular offset 1559 * in an anon_vma, once the anon_vma has been determined, 1560 * this splitting happens to be just what is needed to 1561 * handle where KSM pages have been swapped out: re-reading 1562 * is unnecessarily slow, but we can fix that later on. 1563 */ 1564 if (swap_count(*swap_map) && 1565 PageDirty(page) && PageSwapCache(page)) { 1566 struct writeback_control wbc = { 1567 .sync_mode = WB_SYNC_NONE, 1568 }; 1569 1570 swap_writepage(page, &wbc); 1571 lock_page(page); 1572 wait_on_page_writeback(page); 1573 } 1574 1575 /* 1576 * It is conceivable that a racing task removed this page from 1577 * swap cache just before we acquired the page lock at the top, 1578 * or while we dropped it in unuse_mm(). The page might even 1579 * be back in swap cache on another swap area: that we must not 1580 * delete, since it may not have been written out to swap yet. 1581 */ 1582 if (PageSwapCache(page) && 1583 likely(page_private(page) == entry.val)) 1584 delete_from_swap_cache(page); 1585 1586 /* 1587 * So we could skip searching mms once swap count went 1588 * to 1, we did not mark any present ptes as dirty: must 1589 * mark page dirty so shrink_page_list will preserve it. 1590 */ 1591 SetPageDirty(page); 1592 unlock_page(page); 1593 put_page(page); 1594 1595 /* 1596 * Make sure that we aren't completely killing 1597 * interactive performance. 1598 */ 1599 cond_resched(); 1600 if (frontswap && pages_to_unuse > 0) { 1601 if (!--pages_to_unuse) 1602 break; 1603 } 1604 } 1605 1606 mmput(start_mm); 1607 return retval; 1608 } 1609 1610 /* 1611 * After a successful try_to_unuse, if no swap is now in use, we know 1612 * we can empty the mmlist. swap_lock must be held on entry and exit. 1613 * Note that mmlist_lock nests inside swap_lock, and an mm must be 1614 * added to the mmlist just after page_duplicate - before would be racy. 1615 */ 1616 static void drain_mmlist(void) 1617 { 1618 struct list_head *p, *next; 1619 unsigned int type; 1620 1621 for (type = 0; type < nr_swapfiles; type++) 1622 if (swap_info[type]->inuse_pages) 1623 return; 1624 spin_lock(&mmlist_lock); 1625 list_for_each_safe(p, next, &init_mm.mmlist) 1626 list_del_init(p); 1627 spin_unlock(&mmlist_lock); 1628 } 1629 1630 /* 1631 * Use this swapdev's extent info to locate the (PAGE_SIZE) block which 1632 * corresponds to page offset for the specified swap entry. 1633 * Note that the type of this function is sector_t, but it returns page offset 1634 * into the bdev, not sector offset. 1635 */ 1636 static sector_t map_swap_entry(swp_entry_t entry, struct block_device **bdev) 1637 { 1638 struct swap_info_struct *sis; 1639 struct swap_extent *start_se; 1640 struct swap_extent *se; 1641 pgoff_t offset; 1642 1643 sis = swap_info[swp_type(entry)]; 1644 *bdev = sis->bdev; 1645 1646 offset = swp_offset(entry); 1647 start_se = sis->curr_swap_extent; 1648 se = start_se; 1649 1650 for ( ; ; ) { 1651 if (se->start_page <= offset && 1652 offset < (se->start_page + se->nr_pages)) { 1653 return se->start_block + (offset - se->start_page); 1654 } 1655 se = list_next_entry(se, list); 1656 sis->curr_swap_extent = se; 1657 BUG_ON(se == start_se); /* It *must* be present */ 1658 } 1659 } 1660 1661 /* 1662 * Returns the page offset into bdev for the specified page's swap entry. 1663 */ 1664 sector_t map_swap_page(struct page *page, struct block_device **bdev) 1665 { 1666 swp_entry_t entry; 1667 entry.val = page_private(page); 1668 return map_swap_entry(entry, bdev); 1669 } 1670 1671 /* 1672 * Free all of a swapdev's extent information 1673 */ 1674 static void destroy_swap_extents(struct swap_info_struct *sis) 1675 { 1676 while (!list_empty(&sis->first_swap_extent.list)) { 1677 struct swap_extent *se; 1678 1679 se = list_first_entry(&sis->first_swap_extent.list, 1680 struct swap_extent, list); 1681 list_del(&se->list); 1682 kfree(se); 1683 } 1684 1685 if (sis->flags & SWP_FILE) { 1686 struct file *swap_file = sis->swap_file; 1687 struct address_space *mapping = swap_file->f_mapping; 1688 1689 sis->flags &= ~SWP_FILE; 1690 mapping->a_ops->swap_deactivate(swap_file); 1691 } 1692 } 1693 1694 /* 1695 * Add a block range (and the corresponding page range) into this swapdev's 1696 * extent list. The extent list is kept sorted in page order. 1697 * 1698 * This function rather assumes that it is called in ascending page order. 1699 */ 1700 int 1701 add_swap_extent(struct swap_info_struct *sis, unsigned long start_page, 1702 unsigned long nr_pages, sector_t start_block) 1703 { 1704 struct swap_extent *se; 1705 struct swap_extent *new_se; 1706 struct list_head *lh; 1707 1708 if (start_page == 0) { 1709 se = &sis->first_swap_extent; 1710 sis->curr_swap_extent = se; 1711 se->start_page = 0; 1712 se->nr_pages = nr_pages; 1713 se->start_block = start_block; 1714 return 1; 1715 } else { 1716 lh = sis->first_swap_extent.list.prev; /* Highest extent */ 1717 se = list_entry(lh, struct swap_extent, list); 1718 BUG_ON(se->start_page + se->nr_pages != start_page); 1719 if (se->start_block + se->nr_pages == start_block) { 1720 /* Merge it */ 1721 se->nr_pages += nr_pages; 1722 return 0; 1723 } 1724 } 1725 1726 /* 1727 * No merge. Insert a new extent, preserving ordering. 1728 */ 1729 new_se = kmalloc(sizeof(*se), GFP_KERNEL); 1730 if (new_se == NULL) 1731 return -ENOMEM; 1732 new_se->start_page = start_page; 1733 new_se->nr_pages = nr_pages; 1734 new_se->start_block = start_block; 1735 1736 list_add_tail(&new_se->list, &sis->first_swap_extent.list); 1737 return 1; 1738 } 1739 1740 /* 1741 * A `swap extent' is a simple thing which maps a contiguous range of pages 1742 * onto a contiguous range of disk blocks. An ordered list of swap extents 1743 * is built at swapon time and is then used at swap_writepage/swap_readpage 1744 * time for locating where on disk a page belongs. 1745 * 1746 * If the swapfile is an S_ISBLK block device, a single extent is installed. 1747 * This is done so that the main operating code can treat S_ISBLK and S_ISREG 1748 * swap files identically. 1749 * 1750 * Whether the swapdev is an S_ISREG file or an S_ISBLK blockdev, the swap 1751 * extent list operates in PAGE_SIZE disk blocks. Both S_ISREG and S_ISBLK 1752 * swapfiles are handled *identically* after swapon time. 1753 * 1754 * For S_ISREG swapfiles, setup_swap_extents() will walk all the file's blocks 1755 * and will parse them into an ordered extent list, in PAGE_SIZE chunks. If 1756 * some stray blocks are found which do not fall within the PAGE_SIZE alignment 1757 * requirements, they are simply tossed out - we will never use those blocks 1758 * for swapping. 1759 * 1760 * For S_ISREG swapfiles we set S_SWAPFILE across the life of the swapon. This 1761 * prevents root from shooting her foot off by ftruncating an in-use swapfile, 1762 * which will scribble on the fs. 1763 * 1764 * The amount of disk space which a single swap extent represents varies. 1765 * Typically it is in the 1-4 megabyte range. So we can have hundreds of 1766 * extents in the list. To avoid much list walking, we cache the previous 1767 * search location in `curr_swap_extent', and start new searches from there. 1768 * This is extremely effective. The average number of iterations in 1769 * map_swap_page() has been measured at about 0.3 per page. - akpm. 1770 */ 1771 static int setup_swap_extents(struct swap_info_struct *sis, sector_t *span) 1772 { 1773 struct file *swap_file = sis->swap_file; 1774 struct address_space *mapping = swap_file->f_mapping; 1775 struct inode *inode = mapping->host; 1776 int ret; 1777 1778 if (S_ISBLK(inode->i_mode)) { 1779 ret = add_swap_extent(sis, 0, sis->max, 0); 1780 *span = sis->pages; 1781 return ret; 1782 } 1783 1784 if (mapping->a_ops->swap_activate) { 1785 ret = mapping->a_ops->swap_activate(sis, swap_file, span); 1786 if (!ret) { 1787 sis->flags |= SWP_FILE; 1788 ret = add_swap_extent(sis, 0, sis->max, 0); 1789 *span = sis->pages; 1790 } 1791 return ret; 1792 } 1793 1794 return generic_swapfile_activate(sis, swap_file, span); 1795 } 1796 1797 static void _enable_swap_info(struct swap_info_struct *p, int prio, 1798 unsigned char *swap_map, 1799 struct swap_cluster_info *cluster_info) 1800 { 1801 if (prio >= 0) 1802 p->prio = prio; 1803 else 1804 p->prio = --least_priority; 1805 /* 1806 * the plist prio is negated because plist ordering is 1807 * low-to-high, while swap ordering is high-to-low 1808 */ 1809 p->list.prio = -p->prio; 1810 p->avail_list.prio = -p->prio; 1811 p->swap_map = swap_map; 1812 p->cluster_info = cluster_info; 1813 p->flags |= SWP_WRITEOK; 1814 atomic_long_add(p->pages, &nr_swap_pages); 1815 total_swap_pages += p->pages; 1816 1817 assert_spin_locked(&swap_lock); 1818 /* 1819 * both lists are plists, and thus priority ordered. 1820 * swap_active_head needs to be priority ordered for swapoff(), 1821 * which on removal of any swap_info_struct with an auto-assigned 1822 * (i.e. negative) priority increments the auto-assigned priority 1823 * of any lower-priority swap_info_structs. 1824 * swap_avail_head needs to be priority ordered for get_swap_page(), 1825 * which allocates swap pages from the highest available priority 1826 * swap_info_struct. 1827 */ 1828 plist_add(&p->list, &swap_active_head); 1829 spin_lock(&swap_avail_lock); 1830 plist_add(&p->avail_list, &swap_avail_head); 1831 spin_unlock(&swap_avail_lock); 1832 } 1833 1834 static void enable_swap_info(struct swap_info_struct *p, int prio, 1835 unsigned char *swap_map, 1836 struct swap_cluster_info *cluster_info, 1837 unsigned long *frontswap_map) 1838 { 1839 frontswap_init(p->type, frontswap_map); 1840 spin_lock(&swap_lock); 1841 spin_lock(&p->lock); 1842 _enable_swap_info(p, prio, swap_map, cluster_info); 1843 spin_unlock(&p->lock); 1844 spin_unlock(&swap_lock); 1845 } 1846 1847 static void reinsert_swap_info(struct swap_info_struct *p) 1848 { 1849 spin_lock(&swap_lock); 1850 spin_lock(&p->lock); 1851 _enable_swap_info(p, p->prio, p->swap_map, p->cluster_info); 1852 spin_unlock(&p->lock); 1853 spin_unlock(&swap_lock); 1854 } 1855 1856 SYSCALL_DEFINE1(swapoff, const char __user *, specialfile) 1857 { 1858 struct swap_info_struct *p = NULL; 1859 unsigned char *swap_map; 1860 struct swap_cluster_info *cluster_info; 1861 unsigned long *frontswap_map; 1862 struct file *swap_file, *victim; 1863 struct address_space *mapping; 1864 struct inode *inode; 1865 struct filename *pathname; 1866 int err, found = 0; 1867 unsigned int old_block_size; 1868 1869 if (!capable(CAP_SYS_ADMIN)) 1870 return -EPERM; 1871 1872 BUG_ON(!current->mm); 1873 1874 pathname = getname(specialfile); 1875 if (IS_ERR(pathname)) 1876 return PTR_ERR(pathname); 1877 1878 victim = file_open_name(pathname, O_RDWR|O_LARGEFILE, 0); 1879 err = PTR_ERR(victim); 1880 if (IS_ERR(victim)) 1881 goto out; 1882 1883 mapping = victim->f_mapping; 1884 spin_lock(&swap_lock); 1885 plist_for_each_entry(p, &swap_active_head, list) { 1886 if (p->flags & SWP_WRITEOK) { 1887 if (p->swap_file->f_mapping == mapping) { 1888 found = 1; 1889 break; 1890 } 1891 } 1892 } 1893 if (!found) { 1894 err = -EINVAL; 1895 spin_unlock(&swap_lock); 1896 goto out_dput; 1897 } 1898 if (!security_vm_enough_memory_mm(current->mm, p->pages)) 1899 vm_unacct_memory(p->pages); 1900 else { 1901 err = -ENOMEM; 1902 spin_unlock(&swap_lock); 1903 goto out_dput; 1904 } 1905 spin_lock(&swap_avail_lock); 1906 plist_del(&p->avail_list, &swap_avail_head); 1907 spin_unlock(&swap_avail_lock); 1908 spin_lock(&p->lock); 1909 if (p->prio < 0) { 1910 struct swap_info_struct *si = p; 1911 1912 plist_for_each_entry_continue(si, &swap_active_head, list) { 1913 si->prio++; 1914 si->list.prio--; 1915 si->avail_list.prio--; 1916 } 1917 least_priority++; 1918 } 1919 plist_del(&p->list, &swap_active_head); 1920 atomic_long_sub(p->pages, &nr_swap_pages); 1921 total_swap_pages -= p->pages; 1922 p->flags &= ~SWP_WRITEOK; 1923 spin_unlock(&p->lock); 1924 spin_unlock(&swap_lock); 1925 1926 set_current_oom_origin(); 1927 err = try_to_unuse(p->type, false, 0); /* force unuse all pages */ 1928 clear_current_oom_origin(); 1929 1930 if (err) { 1931 /* re-insert swap space back into swap_list */ 1932 reinsert_swap_info(p); 1933 goto out_dput; 1934 } 1935 1936 flush_work(&p->discard_work); 1937 1938 destroy_swap_extents(p); 1939 if (p->flags & SWP_CONTINUED) 1940 free_swap_count_continuations(p); 1941 1942 mutex_lock(&swapon_mutex); 1943 spin_lock(&swap_lock); 1944 spin_lock(&p->lock); 1945 drain_mmlist(); 1946 1947 /* wait for anyone still in scan_swap_map */ 1948 p->highest_bit = 0; /* cuts scans short */ 1949 while (p->flags >= SWP_SCANNING) { 1950 spin_unlock(&p->lock); 1951 spin_unlock(&swap_lock); 1952 schedule_timeout_uninterruptible(1); 1953 spin_lock(&swap_lock); 1954 spin_lock(&p->lock); 1955 } 1956 1957 swap_file = p->swap_file; 1958 old_block_size = p->old_block_size; 1959 p->swap_file = NULL; 1960 p->max = 0; 1961 swap_map = p->swap_map; 1962 p->swap_map = NULL; 1963 cluster_info = p->cluster_info; 1964 p->cluster_info = NULL; 1965 frontswap_map = frontswap_map_get(p); 1966 spin_unlock(&p->lock); 1967 spin_unlock(&swap_lock); 1968 frontswap_invalidate_area(p->type); 1969 frontswap_map_set(p, NULL); 1970 mutex_unlock(&swapon_mutex); 1971 free_percpu(p->percpu_cluster); 1972 p->percpu_cluster = NULL; 1973 vfree(swap_map); 1974 vfree(cluster_info); 1975 vfree(frontswap_map); 1976 /* Destroy swap account information */ 1977 swap_cgroup_swapoff(p->type); 1978 1979 inode = mapping->host; 1980 if (S_ISBLK(inode->i_mode)) { 1981 struct block_device *bdev = I_BDEV(inode); 1982 set_blocksize(bdev, old_block_size); 1983 blkdev_put(bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL); 1984 } else { 1985 inode_lock(inode); 1986 inode->i_flags &= ~S_SWAPFILE; 1987 inode_unlock(inode); 1988 } 1989 filp_close(swap_file, NULL); 1990 1991 /* 1992 * Clear the SWP_USED flag after all resources are freed so that swapon 1993 * can reuse this swap_info in alloc_swap_info() safely. It is ok to 1994 * not hold p->lock after we cleared its SWP_WRITEOK. 1995 */ 1996 spin_lock(&swap_lock); 1997 p->flags = 0; 1998 spin_unlock(&swap_lock); 1999 2000 err = 0; 2001 atomic_inc(&proc_poll_event); 2002 wake_up_interruptible(&proc_poll_wait); 2003 2004 out_dput: 2005 filp_close(victim, NULL); 2006 out: 2007 putname(pathname); 2008 return err; 2009 } 2010 2011 #ifdef CONFIG_PROC_FS 2012 static unsigned swaps_poll(struct file *file, poll_table *wait) 2013 { 2014 struct seq_file *seq = file->private_data; 2015 2016 poll_wait(file, &proc_poll_wait, wait); 2017 2018 if (seq->poll_event != atomic_read(&proc_poll_event)) { 2019 seq->poll_event = atomic_read(&proc_poll_event); 2020 return POLLIN | POLLRDNORM | POLLERR | POLLPRI; 2021 } 2022 2023 return POLLIN | POLLRDNORM; 2024 } 2025 2026 /* iterator */ 2027 static void *swap_start(struct seq_file *swap, loff_t *pos) 2028 { 2029 struct swap_info_struct *si; 2030 int type; 2031 loff_t l = *pos; 2032 2033 mutex_lock(&swapon_mutex); 2034 2035 if (!l) 2036 return SEQ_START_TOKEN; 2037 2038 for (type = 0; type < nr_swapfiles; type++) { 2039 smp_rmb(); /* read nr_swapfiles before swap_info[type] */ 2040 si = swap_info[type]; 2041 if (!(si->flags & SWP_USED) || !si->swap_map) 2042 continue; 2043 if (!--l) 2044 return si; 2045 } 2046 2047 return NULL; 2048 } 2049 2050 static void *swap_next(struct seq_file *swap, void *v, loff_t *pos) 2051 { 2052 struct swap_info_struct *si = v; 2053 int type; 2054 2055 if (v == SEQ_START_TOKEN) 2056 type = 0; 2057 else 2058 type = si->type + 1; 2059 2060 for (; type < nr_swapfiles; type++) { 2061 smp_rmb(); /* read nr_swapfiles before swap_info[type] */ 2062 si = swap_info[type]; 2063 if (!(si->flags & SWP_USED) || !si->swap_map) 2064 continue; 2065 ++*pos; 2066 return si; 2067 } 2068 2069 return NULL; 2070 } 2071 2072 static void swap_stop(struct seq_file *swap, void *v) 2073 { 2074 mutex_unlock(&swapon_mutex); 2075 } 2076 2077 static int swap_show(struct seq_file *swap, void *v) 2078 { 2079 struct swap_info_struct *si = v; 2080 struct file *file; 2081 int len; 2082 2083 if (si == SEQ_START_TOKEN) { 2084 seq_puts(swap,"Filename\t\t\t\tType\t\tSize\tUsed\tPriority\n"); 2085 return 0; 2086 } 2087 2088 file = si->swap_file; 2089 len = seq_file_path(swap, file, " \t\n\\"); 2090 seq_printf(swap, "%*s%s\t%u\t%u\t%d\n", 2091 len < 40 ? 40 - len : 1, " ", 2092 S_ISBLK(file_inode(file)->i_mode) ? 2093 "partition" : "file\t", 2094 si->pages << (PAGE_SHIFT - 10), 2095 si->inuse_pages << (PAGE_SHIFT - 10), 2096 si->prio); 2097 return 0; 2098 } 2099 2100 static const struct seq_operations swaps_op = { 2101 .start = swap_start, 2102 .next = swap_next, 2103 .stop = swap_stop, 2104 .show = swap_show 2105 }; 2106 2107 static int swaps_open(struct inode *inode, struct file *file) 2108 { 2109 struct seq_file *seq; 2110 int ret; 2111 2112 ret = seq_open(file, &swaps_op); 2113 if (ret) 2114 return ret; 2115 2116 seq = file->private_data; 2117 seq->poll_event = atomic_read(&proc_poll_event); 2118 return 0; 2119 } 2120 2121 static const struct file_operations proc_swaps_operations = { 2122 .open = swaps_open, 2123 .read = seq_read, 2124 .llseek = seq_lseek, 2125 .release = seq_release, 2126 .poll = swaps_poll, 2127 }; 2128 2129 static int __init procswaps_init(void) 2130 { 2131 proc_create("swaps", 0, NULL, &proc_swaps_operations); 2132 return 0; 2133 } 2134 __initcall(procswaps_init); 2135 #endif /* CONFIG_PROC_FS */ 2136 2137 #ifdef MAX_SWAPFILES_CHECK 2138 static int __init max_swapfiles_check(void) 2139 { 2140 MAX_SWAPFILES_CHECK(); 2141 return 0; 2142 } 2143 late_initcall(max_swapfiles_check); 2144 #endif 2145 2146 static struct swap_info_struct *alloc_swap_info(void) 2147 { 2148 struct swap_info_struct *p; 2149 unsigned int type; 2150 2151 p = kzalloc(sizeof(*p), GFP_KERNEL); 2152 if (!p) 2153 return ERR_PTR(-ENOMEM); 2154 2155 spin_lock(&swap_lock); 2156 for (type = 0; type < nr_swapfiles; type++) { 2157 if (!(swap_info[type]->flags & SWP_USED)) 2158 break; 2159 } 2160 if (type >= MAX_SWAPFILES) { 2161 spin_unlock(&swap_lock); 2162 kfree(p); 2163 return ERR_PTR(-EPERM); 2164 } 2165 if (type >= nr_swapfiles) { 2166 p->type = type; 2167 swap_info[type] = p; 2168 /* 2169 * Write swap_info[type] before nr_swapfiles, in case a 2170 * racing procfs swap_start() or swap_next() is reading them. 2171 * (We never shrink nr_swapfiles, we never free this entry.) 2172 */ 2173 smp_wmb(); 2174 nr_swapfiles++; 2175 } else { 2176 kfree(p); 2177 p = swap_info[type]; 2178 /* 2179 * Do not memset this entry: a racing procfs swap_next() 2180 * would be relying on p->type to remain valid. 2181 */ 2182 } 2183 INIT_LIST_HEAD(&p->first_swap_extent.list); 2184 plist_node_init(&p->list, 0); 2185 plist_node_init(&p->avail_list, 0); 2186 p->flags = SWP_USED; 2187 spin_unlock(&swap_lock); 2188 spin_lock_init(&p->lock); 2189 2190 return p; 2191 } 2192 2193 static int claim_swapfile(struct swap_info_struct *p, struct inode *inode) 2194 { 2195 int error; 2196 2197 if (S_ISBLK(inode->i_mode)) { 2198 p->bdev = bdgrab(I_BDEV(inode)); 2199 error = blkdev_get(p->bdev, 2200 FMODE_READ | FMODE_WRITE | FMODE_EXCL, p); 2201 if (error < 0) { 2202 p->bdev = NULL; 2203 return error; 2204 } 2205 p->old_block_size = block_size(p->bdev); 2206 error = set_blocksize(p->bdev, PAGE_SIZE); 2207 if (error < 0) 2208 return error; 2209 p->flags |= SWP_BLKDEV; 2210 } else if (S_ISREG(inode->i_mode)) { 2211 p->bdev = inode->i_sb->s_bdev; 2212 inode_lock(inode); 2213 if (IS_SWAPFILE(inode)) 2214 return -EBUSY; 2215 } else 2216 return -EINVAL; 2217 2218 return 0; 2219 } 2220 2221 static unsigned long read_swap_header(struct swap_info_struct *p, 2222 union swap_header *swap_header, 2223 struct inode *inode) 2224 { 2225 int i; 2226 unsigned long maxpages; 2227 unsigned long swapfilepages; 2228 unsigned long last_page; 2229 2230 if (memcmp("SWAPSPACE2", swap_header->magic.magic, 10)) { 2231 pr_err("Unable to find swap-space signature\n"); 2232 return 0; 2233 } 2234 2235 /* swap partition endianess hack... */ 2236 if (swab32(swap_header->info.version) == 1) { 2237 swab32s(&swap_header->info.version); 2238 swab32s(&swap_header->info.last_page); 2239 swab32s(&swap_header->info.nr_badpages); 2240 if (swap_header->info.nr_badpages > MAX_SWAP_BADPAGES) 2241 return 0; 2242 for (i = 0; i < swap_header->info.nr_badpages; i++) 2243 swab32s(&swap_header->info.badpages[i]); 2244 } 2245 /* Check the swap header's sub-version */ 2246 if (swap_header->info.version != 1) { 2247 pr_warn("Unable to handle swap header version %d\n", 2248 swap_header->info.version); 2249 return 0; 2250 } 2251 2252 p->lowest_bit = 1; 2253 p->cluster_next = 1; 2254 p->cluster_nr = 0; 2255 2256 /* 2257 * Find out how many pages are allowed for a single swap 2258 * device. There are two limiting factors: 1) the number 2259 * of bits for the swap offset in the swp_entry_t type, and 2260 * 2) the number of bits in the swap pte as defined by the 2261 * different architectures. In order to find the 2262 * largest possible bit mask, a swap entry with swap type 0 2263 * and swap offset ~0UL is created, encoded to a swap pte, 2264 * decoded to a swp_entry_t again, and finally the swap 2265 * offset is extracted. This will mask all the bits from 2266 * the initial ~0UL mask that can't be encoded in either 2267 * the swp_entry_t or the architecture definition of a 2268 * swap pte. 2269 */ 2270 maxpages = swp_offset(pte_to_swp_entry( 2271 swp_entry_to_pte(swp_entry(0, ~0UL)))) + 1; 2272 last_page = swap_header->info.last_page; 2273 if (last_page > maxpages) { 2274 pr_warn("Truncating oversized swap area, only using %luk out of %luk\n", 2275 maxpages << (PAGE_SHIFT - 10), 2276 last_page << (PAGE_SHIFT - 10)); 2277 } 2278 if (maxpages > last_page) { 2279 maxpages = last_page + 1; 2280 /* p->max is an unsigned int: don't overflow it */ 2281 if ((unsigned int)maxpages == 0) 2282 maxpages = UINT_MAX; 2283 } 2284 p->highest_bit = maxpages - 1; 2285 2286 if (!maxpages) 2287 return 0; 2288 swapfilepages = i_size_read(inode) >> PAGE_SHIFT; 2289 if (swapfilepages && maxpages > swapfilepages) { 2290 pr_warn("Swap area shorter than signature indicates\n"); 2291 return 0; 2292 } 2293 if (swap_header->info.nr_badpages && S_ISREG(inode->i_mode)) 2294 return 0; 2295 if (swap_header->info.nr_badpages > MAX_SWAP_BADPAGES) 2296 return 0; 2297 2298 return maxpages; 2299 } 2300 2301 static int setup_swap_map_and_extents(struct swap_info_struct *p, 2302 union swap_header *swap_header, 2303 unsigned char *swap_map, 2304 struct swap_cluster_info *cluster_info, 2305 unsigned long maxpages, 2306 sector_t *span) 2307 { 2308 int i; 2309 unsigned int nr_good_pages; 2310 int nr_extents; 2311 unsigned long nr_clusters = DIV_ROUND_UP(maxpages, SWAPFILE_CLUSTER); 2312 unsigned long idx = p->cluster_next / SWAPFILE_CLUSTER; 2313 2314 nr_good_pages = maxpages - 1; /* omit header page */ 2315 2316 cluster_list_init(&p->free_clusters); 2317 cluster_list_init(&p->discard_clusters); 2318 2319 for (i = 0; i < swap_header->info.nr_badpages; i++) { 2320 unsigned int page_nr = swap_header->info.badpages[i]; 2321 if (page_nr == 0 || page_nr > swap_header->info.last_page) 2322 return -EINVAL; 2323 if (page_nr < maxpages) { 2324 swap_map[page_nr] = SWAP_MAP_BAD; 2325 nr_good_pages--; 2326 /* 2327 * Haven't marked the cluster free yet, no list 2328 * operation involved 2329 */ 2330 inc_cluster_info_page(p, cluster_info, page_nr); 2331 } 2332 } 2333 2334 /* Haven't marked the cluster free yet, no list operation involved */ 2335 for (i = maxpages; i < round_up(maxpages, SWAPFILE_CLUSTER); i++) 2336 inc_cluster_info_page(p, cluster_info, i); 2337 2338 if (nr_good_pages) { 2339 swap_map[0] = SWAP_MAP_BAD; 2340 /* 2341 * Not mark the cluster free yet, no list 2342 * operation involved 2343 */ 2344 inc_cluster_info_page(p, cluster_info, 0); 2345 p->max = maxpages; 2346 p->pages = nr_good_pages; 2347 nr_extents = setup_swap_extents(p, span); 2348 if (nr_extents < 0) 2349 return nr_extents; 2350 nr_good_pages = p->pages; 2351 } 2352 if (!nr_good_pages) { 2353 pr_warn("Empty swap-file\n"); 2354 return -EINVAL; 2355 } 2356 2357 if (!cluster_info) 2358 return nr_extents; 2359 2360 for (i = 0; i < nr_clusters; i++) { 2361 if (!cluster_count(&cluster_info[idx])) { 2362 cluster_set_flag(&cluster_info[idx], CLUSTER_FLAG_FREE); 2363 cluster_list_add_tail(&p->free_clusters, cluster_info, 2364 idx); 2365 } 2366 idx++; 2367 if (idx == nr_clusters) 2368 idx = 0; 2369 } 2370 return nr_extents; 2371 } 2372 2373 /* 2374 * Helper to sys_swapon determining if a given swap 2375 * backing device queue supports DISCARD operations. 2376 */ 2377 static bool swap_discardable(struct swap_info_struct *si) 2378 { 2379 struct request_queue *q = bdev_get_queue(si->bdev); 2380 2381 if (!q || !blk_queue_discard(q)) 2382 return false; 2383 2384 return true; 2385 } 2386 2387 SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags) 2388 { 2389 struct swap_info_struct *p; 2390 struct filename *name; 2391 struct file *swap_file = NULL; 2392 struct address_space *mapping; 2393 int prio; 2394 int error; 2395 union swap_header *swap_header; 2396 int nr_extents; 2397 sector_t span; 2398 unsigned long maxpages; 2399 unsigned char *swap_map = NULL; 2400 struct swap_cluster_info *cluster_info = NULL; 2401 unsigned long *frontswap_map = NULL; 2402 struct page *page = NULL; 2403 struct inode *inode = NULL; 2404 2405 if (swap_flags & ~SWAP_FLAGS_VALID) 2406 return -EINVAL; 2407 2408 if (!capable(CAP_SYS_ADMIN)) 2409 return -EPERM; 2410 2411 p = alloc_swap_info(); 2412 if (IS_ERR(p)) 2413 return PTR_ERR(p); 2414 2415 INIT_WORK(&p->discard_work, swap_discard_work); 2416 2417 name = getname(specialfile); 2418 if (IS_ERR(name)) { 2419 error = PTR_ERR(name); 2420 name = NULL; 2421 goto bad_swap; 2422 } 2423 swap_file = file_open_name(name, O_RDWR|O_LARGEFILE, 0); 2424 if (IS_ERR(swap_file)) { 2425 error = PTR_ERR(swap_file); 2426 swap_file = NULL; 2427 goto bad_swap; 2428 } 2429 2430 p->swap_file = swap_file; 2431 mapping = swap_file->f_mapping; 2432 inode = mapping->host; 2433 2434 /* If S_ISREG(inode->i_mode) will do inode_lock(inode); */ 2435 error = claim_swapfile(p, inode); 2436 if (unlikely(error)) 2437 goto bad_swap; 2438 2439 /* 2440 * Read the swap header. 2441 */ 2442 if (!mapping->a_ops->readpage) { 2443 error = -EINVAL; 2444 goto bad_swap; 2445 } 2446 page = read_mapping_page(mapping, 0, swap_file); 2447 if (IS_ERR(page)) { 2448 error = PTR_ERR(page); 2449 goto bad_swap; 2450 } 2451 swap_header = kmap(page); 2452 2453 maxpages = read_swap_header(p, swap_header, inode); 2454 if (unlikely(!maxpages)) { 2455 error = -EINVAL; 2456 goto bad_swap; 2457 } 2458 2459 /* OK, set up the swap map and apply the bad block list */ 2460 swap_map = vzalloc(maxpages); 2461 if (!swap_map) { 2462 error = -ENOMEM; 2463 goto bad_swap; 2464 } 2465 2466 if (bdi_cap_stable_pages_required(inode_to_bdi(inode))) 2467 p->flags |= SWP_STABLE_WRITES; 2468 2469 if (p->bdev && blk_queue_nonrot(bdev_get_queue(p->bdev))) { 2470 int cpu; 2471 2472 p->flags |= SWP_SOLIDSTATE; 2473 /* 2474 * select a random position to start with to help wear leveling 2475 * SSD 2476 */ 2477 p->cluster_next = 1 + (prandom_u32() % p->highest_bit); 2478 2479 cluster_info = vzalloc(DIV_ROUND_UP(maxpages, 2480 SWAPFILE_CLUSTER) * sizeof(*cluster_info)); 2481 if (!cluster_info) { 2482 error = -ENOMEM; 2483 goto bad_swap; 2484 } 2485 p->percpu_cluster = alloc_percpu(struct percpu_cluster); 2486 if (!p->percpu_cluster) { 2487 error = -ENOMEM; 2488 goto bad_swap; 2489 } 2490 for_each_possible_cpu(cpu) { 2491 struct percpu_cluster *cluster; 2492 cluster = per_cpu_ptr(p->percpu_cluster, cpu); 2493 cluster_set_null(&cluster->index); 2494 } 2495 } 2496 2497 error = swap_cgroup_swapon(p->type, maxpages); 2498 if (error) 2499 goto bad_swap; 2500 2501 nr_extents = setup_swap_map_and_extents(p, swap_header, swap_map, 2502 cluster_info, maxpages, &span); 2503 if (unlikely(nr_extents < 0)) { 2504 error = nr_extents; 2505 goto bad_swap; 2506 } 2507 /* frontswap enabled? set up bit-per-page map for frontswap */ 2508 if (IS_ENABLED(CONFIG_FRONTSWAP)) 2509 frontswap_map = vzalloc(BITS_TO_LONGS(maxpages) * sizeof(long)); 2510 2511 if (p->bdev &&(swap_flags & SWAP_FLAG_DISCARD) && swap_discardable(p)) { 2512 /* 2513 * When discard is enabled for swap with no particular 2514 * policy flagged, we set all swap discard flags here in 2515 * order to sustain backward compatibility with older 2516 * swapon(8) releases. 2517 */ 2518 p->flags |= (SWP_DISCARDABLE | SWP_AREA_DISCARD | 2519 SWP_PAGE_DISCARD); 2520 2521 /* 2522 * By flagging sys_swapon, a sysadmin can tell us to 2523 * either do single-time area discards only, or to just 2524 * perform discards for released swap page-clusters. 2525 * Now it's time to adjust the p->flags accordingly. 2526 */ 2527 if (swap_flags & SWAP_FLAG_DISCARD_ONCE) 2528 p->flags &= ~SWP_PAGE_DISCARD; 2529 else if (swap_flags & SWAP_FLAG_DISCARD_PAGES) 2530 p->flags &= ~SWP_AREA_DISCARD; 2531 2532 /* issue a swapon-time discard if it's still required */ 2533 if (p->flags & SWP_AREA_DISCARD) { 2534 int err = discard_swap(p); 2535 if (unlikely(err)) 2536 pr_err("swapon: discard_swap(%p): %d\n", 2537 p, err); 2538 } 2539 } 2540 2541 mutex_lock(&swapon_mutex); 2542 prio = -1; 2543 if (swap_flags & SWAP_FLAG_PREFER) 2544 prio = 2545 (swap_flags & SWAP_FLAG_PRIO_MASK) >> SWAP_FLAG_PRIO_SHIFT; 2546 enable_swap_info(p, prio, swap_map, cluster_info, frontswap_map); 2547 2548 pr_info("Adding %uk swap on %s. Priority:%d extents:%d across:%lluk %s%s%s%s%s\n", 2549 p->pages<<(PAGE_SHIFT-10), name->name, p->prio, 2550 nr_extents, (unsigned long long)span<<(PAGE_SHIFT-10), 2551 (p->flags & SWP_SOLIDSTATE) ? "SS" : "", 2552 (p->flags & SWP_DISCARDABLE) ? "D" : "", 2553 (p->flags & SWP_AREA_DISCARD) ? "s" : "", 2554 (p->flags & SWP_PAGE_DISCARD) ? "c" : "", 2555 (frontswap_map) ? "FS" : ""); 2556 2557 mutex_unlock(&swapon_mutex); 2558 atomic_inc(&proc_poll_event); 2559 wake_up_interruptible(&proc_poll_wait); 2560 2561 if (S_ISREG(inode->i_mode)) 2562 inode->i_flags |= S_SWAPFILE; 2563 error = 0; 2564 goto out; 2565 bad_swap: 2566 free_percpu(p->percpu_cluster); 2567 p->percpu_cluster = NULL; 2568 if (inode && S_ISBLK(inode->i_mode) && p->bdev) { 2569 set_blocksize(p->bdev, p->old_block_size); 2570 blkdev_put(p->bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL); 2571 } 2572 destroy_swap_extents(p); 2573 swap_cgroup_swapoff(p->type); 2574 spin_lock(&swap_lock); 2575 p->swap_file = NULL; 2576 p->flags = 0; 2577 spin_unlock(&swap_lock); 2578 vfree(swap_map); 2579 vfree(cluster_info); 2580 if (swap_file) { 2581 if (inode && S_ISREG(inode->i_mode)) { 2582 inode_unlock(inode); 2583 inode = NULL; 2584 } 2585 filp_close(swap_file, NULL); 2586 } 2587 out: 2588 if (page && !IS_ERR(page)) { 2589 kunmap(page); 2590 put_page(page); 2591 } 2592 if (name) 2593 putname(name); 2594 if (inode && S_ISREG(inode->i_mode)) 2595 inode_unlock(inode); 2596 return error; 2597 } 2598 2599 void si_swapinfo(struct sysinfo *val) 2600 { 2601 unsigned int type; 2602 unsigned long nr_to_be_unused = 0; 2603 2604 spin_lock(&swap_lock); 2605 for (type = 0; type < nr_swapfiles; type++) { 2606 struct swap_info_struct *si = swap_info[type]; 2607 2608 if ((si->flags & SWP_USED) && !(si->flags & SWP_WRITEOK)) 2609 nr_to_be_unused += si->inuse_pages; 2610 } 2611 val->freeswap = atomic_long_read(&nr_swap_pages) + nr_to_be_unused; 2612 val->totalswap = total_swap_pages + nr_to_be_unused; 2613 spin_unlock(&swap_lock); 2614 } 2615 2616 /* 2617 * Verify that a swap entry is valid and increment its swap map count. 2618 * 2619 * Returns error code in following case. 2620 * - success -> 0 2621 * - swp_entry is invalid -> EINVAL 2622 * - swp_entry is migration entry -> EINVAL 2623 * - swap-cache reference is requested but there is already one. -> EEXIST 2624 * - swap-cache reference is requested but the entry is not used. -> ENOENT 2625 * - swap-mapped reference requested but needs continued swap count. -> ENOMEM 2626 */ 2627 static int __swap_duplicate(swp_entry_t entry, unsigned char usage) 2628 { 2629 struct swap_info_struct *p; 2630 unsigned long offset, type; 2631 unsigned char count; 2632 unsigned char has_cache; 2633 int err = -EINVAL; 2634 2635 if (non_swap_entry(entry)) 2636 goto out; 2637 2638 type = swp_type(entry); 2639 if (type >= nr_swapfiles) 2640 goto bad_file; 2641 p = swap_info[type]; 2642 offset = swp_offset(entry); 2643 2644 spin_lock(&p->lock); 2645 if (unlikely(offset >= p->max)) 2646 goto unlock_out; 2647 2648 count = p->swap_map[offset]; 2649 2650 /* 2651 * swapin_readahead() doesn't check if a swap entry is valid, so the 2652 * swap entry could be SWAP_MAP_BAD. Check here with lock held. 2653 */ 2654 if (unlikely(swap_count(count) == SWAP_MAP_BAD)) { 2655 err = -ENOENT; 2656 goto unlock_out; 2657 } 2658 2659 has_cache = count & SWAP_HAS_CACHE; 2660 count &= ~SWAP_HAS_CACHE; 2661 err = 0; 2662 2663 if (usage == SWAP_HAS_CACHE) { 2664 2665 /* set SWAP_HAS_CACHE if there is no cache and entry is used */ 2666 if (!has_cache && count) 2667 has_cache = SWAP_HAS_CACHE; 2668 else if (has_cache) /* someone else added cache */ 2669 err = -EEXIST; 2670 else /* no users remaining */ 2671 err = -ENOENT; 2672 2673 } else if (count || has_cache) { 2674 2675 if ((count & ~COUNT_CONTINUED) < SWAP_MAP_MAX) 2676 count += usage; 2677 else if ((count & ~COUNT_CONTINUED) > SWAP_MAP_MAX) 2678 err = -EINVAL; 2679 else if (swap_count_continued(p, offset, count)) 2680 count = COUNT_CONTINUED; 2681 else 2682 err = -ENOMEM; 2683 } else 2684 err = -ENOENT; /* unused swap entry */ 2685 2686 p->swap_map[offset] = count | has_cache; 2687 2688 unlock_out: 2689 spin_unlock(&p->lock); 2690 out: 2691 return err; 2692 2693 bad_file: 2694 pr_err("swap_dup: %s%08lx\n", Bad_file, entry.val); 2695 goto out; 2696 } 2697 2698 /* 2699 * Help swapoff by noting that swap entry belongs to shmem/tmpfs 2700 * (in which case its reference count is never incremented). 2701 */ 2702 void swap_shmem_alloc(swp_entry_t entry) 2703 { 2704 __swap_duplicate(entry, SWAP_MAP_SHMEM); 2705 } 2706 2707 /* 2708 * Increase reference count of swap entry by 1. 2709 * Returns 0 for success, or -ENOMEM if a swap_count_continuation is required 2710 * but could not be atomically allocated. Returns 0, just as if it succeeded, 2711 * if __swap_duplicate() fails for another reason (-EINVAL or -ENOENT), which 2712 * might occur if a page table entry has got corrupted. 2713 */ 2714 int swap_duplicate(swp_entry_t entry) 2715 { 2716 int err = 0; 2717 2718 while (!err && __swap_duplicate(entry, 1) == -ENOMEM) 2719 err = add_swap_count_continuation(entry, GFP_ATOMIC); 2720 return err; 2721 } 2722 2723 /* 2724 * @entry: swap entry for which we allocate swap cache. 2725 * 2726 * Called when allocating swap cache for existing swap entry, 2727 * This can return error codes. Returns 0 at success. 2728 * -EBUSY means there is a swap cache. 2729 * Note: return code is different from swap_duplicate(). 2730 */ 2731 int swapcache_prepare(swp_entry_t entry) 2732 { 2733 return __swap_duplicate(entry, SWAP_HAS_CACHE); 2734 } 2735 2736 struct swap_info_struct *page_swap_info(struct page *page) 2737 { 2738 swp_entry_t swap = { .val = page_private(page) }; 2739 return swap_info[swp_type(swap)]; 2740 } 2741 2742 /* 2743 * out-of-line __page_file_ methods to avoid include hell. 2744 */ 2745 struct address_space *__page_file_mapping(struct page *page) 2746 { 2747 VM_BUG_ON_PAGE(!PageSwapCache(page), page); 2748 return page_swap_info(page)->swap_file->f_mapping; 2749 } 2750 EXPORT_SYMBOL_GPL(__page_file_mapping); 2751 2752 pgoff_t __page_file_index(struct page *page) 2753 { 2754 swp_entry_t swap = { .val = page_private(page) }; 2755 VM_BUG_ON_PAGE(!PageSwapCache(page), page); 2756 return swp_offset(swap); 2757 } 2758 EXPORT_SYMBOL_GPL(__page_file_index); 2759 2760 /* 2761 * add_swap_count_continuation - called when a swap count is duplicated 2762 * beyond SWAP_MAP_MAX, it allocates a new page and links that to the entry's 2763 * page of the original vmalloc'ed swap_map, to hold the continuation count 2764 * (for that entry and for its neighbouring PAGE_SIZE swap entries). Called 2765 * again when count is duplicated beyond SWAP_MAP_MAX * SWAP_CONT_MAX, etc. 2766 * 2767 * These continuation pages are seldom referenced: the common paths all work 2768 * on the original swap_map, only referring to a continuation page when the 2769 * low "digit" of a count is incremented or decremented through SWAP_MAP_MAX. 2770 * 2771 * add_swap_count_continuation(, GFP_ATOMIC) can be called while holding 2772 * page table locks; if it fails, add_swap_count_continuation(, GFP_KERNEL) 2773 * can be called after dropping locks. 2774 */ 2775 int add_swap_count_continuation(swp_entry_t entry, gfp_t gfp_mask) 2776 { 2777 struct swap_info_struct *si; 2778 struct page *head; 2779 struct page *page; 2780 struct page *list_page; 2781 pgoff_t offset; 2782 unsigned char count; 2783 2784 /* 2785 * When debugging, it's easier to use __GFP_ZERO here; but it's better 2786 * for latency not to zero a page while GFP_ATOMIC and holding locks. 2787 */ 2788 page = alloc_page(gfp_mask | __GFP_HIGHMEM); 2789 2790 si = swap_info_get(entry); 2791 if (!si) { 2792 /* 2793 * An acceptable race has occurred since the failing 2794 * __swap_duplicate(): the swap entry has been freed, 2795 * perhaps even the whole swap_map cleared for swapoff. 2796 */ 2797 goto outer; 2798 } 2799 2800 offset = swp_offset(entry); 2801 count = si->swap_map[offset] & ~SWAP_HAS_CACHE; 2802 2803 if ((count & ~COUNT_CONTINUED) != SWAP_MAP_MAX) { 2804 /* 2805 * The higher the swap count, the more likely it is that tasks 2806 * will race to add swap count continuation: we need to avoid 2807 * over-provisioning. 2808 */ 2809 goto out; 2810 } 2811 2812 if (!page) { 2813 spin_unlock(&si->lock); 2814 return -ENOMEM; 2815 } 2816 2817 /* 2818 * We are fortunate that although vmalloc_to_page uses pte_offset_map, 2819 * no architecture is using highmem pages for kernel page tables: so it 2820 * will not corrupt the GFP_ATOMIC caller's atomic page table kmaps. 2821 */ 2822 head = vmalloc_to_page(si->swap_map + offset); 2823 offset &= ~PAGE_MASK; 2824 2825 /* 2826 * Page allocation does not initialize the page's lru field, 2827 * but it does always reset its private field. 2828 */ 2829 if (!page_private(head)) { 2830 BUG_ON(count & COUNT_CONTINUED); 2831 INIT_LIST_HEAD(&head->lru); 2832 set_page_private(head, SWP_CONTINUED); 2833 si->flags |= SWP_CONTINUED; 2834 } 2835 2836 list_for_each_entry(list_page, &head->lru, lru) { 2837 unsigned char *map; 2838 2839 /* 2840 * If the previous map said no continuation, but we've found 2841 * a continuation page, free our allocation and use this one. 2842 */ 2843 if (!(count & COUNT_CONTINUED)) 2844 goto out; 2845 2846 map = kmap_atomic(list_page) + offset; 2847 count = *map; 2848 kunmap_atomic(map); 2849 2850 /* 2851 * If this continuation count now has some space in it, 2852 * free our allocation and use this one. 2853 */ 2854 if ((count & ~COUNT_CONTINUED) != SWAP_CONT_MAX) 2855 goto out; 2856 } 2857 2858 list_add_tail(&page->lru, &head->lru); 2859 page = NULL; /* now it's attached, don't free it */ 2860 out: 2861 spin_unlock(&si->lock); 2862 outer: 2863 if (page) 2864 __free_page(page); 2865 return 0; 2866 } 2867 2868 /* 2869 * swap_count_continued - when the original swap_map count is incremented 2870 * from SWAP_MAP_MAX, check if there is already a continuation page to carry 2871 * into, carry if so, or else fail until a new continuation page is allocated; 2872 * when the original swap_map count is decremented from 0 with continuation, 2873 * borrow from the continuation and report whether it still holds more. 2874 * Called while __swap_duplicate() or swap_entry_free() holds swap_lock. 2875 */ 2876 static bool swap_count_continued(struct swap_info_struct *si, 2877 pgoff_t offset, unsigned char count) 2878 { 2879 struct page *head; 2880 struct page *page; 2881 unsigned char *map; 2882 2883 head = vmalloc_to_page(si->swap_map + offset); 2884 if (page_private(head) != SWP_CONTINUED) { 2885 BUG_ON(count & COUNT_CONTINUED); 2886 return false; /* need to add count continuation */ 2887 } 2888 2889 offset &= ~PAGE_MASK; 2890 page = list_entry(head->lru.next, struct page, lru); 2891 map = kmap_atomic(page) + offset; 2892 2893 if (count == SWAP_MAP_MAX) /* initial increment from swap_map */ 2894 goto init_map; /* jump over SWAP_CONT_MAX checks */ 2895 2896 if (count == (SWAP_MAP_MAX | COUNT_CONTINUED)) { /* incrementing */ 2897 /* 2898 * Think of how you add 1 to 999 2899 */ 2900 while (*map == (SWAP_CONT_MAX | COUNT_CONTINUED)) { 2901 kunmap_atomic(map); 2902 page = list_entry(page->lru.next, struct page, lru); 2903 BUG_ON(page == head); 2904 map = kmap_atomic(page) + offset; 2905 } 2906 if (*map == SWAP_CONT_MAX) { 2907 kunmap_atomic(map); 2908 page = list_entry(page->lru.next, struct page, lru); 2909 if (page == head) 2910 return false; /* add count continuation */ 2911 map = kmap_atomic(page) + offset; 2912 init_map: *map = 0; /* we didn't zero the page */ 2913 } 2914 *map += 1; 2915 kunmap_atomic(map); 2916 page = list_entry(page->lru.prev, struct page, lru); 2917 while (page != head) { 2918 map = kmap_atomic(page) + offset; 2919 *map = COUNT_CONTINUED; 2920 kunmap_atomic(map); 2921 page = list_entry(page->lru.prev, struct page, lru); 2922 } 2923 return true; /* incremented */ 2924 2925 } else { /* decrementing */ 2926 /* 2927 * Think of how you subtract 1 from 1000 2928 */ 2929 BUG_ON(count != COUNT_CONTINUED); 2930 while (*map == COUNT_CONTINUED) { 2931 kunmap_atomic(map); 2932 page = list_entry(page->lru.next, struct page, lru); 2933 BUG_ON(page == head); 2934 map = kmap_atomic(page) + offset; 2935 } 2936 BUG_ON(*map == 0); 2937 *map -= 1; 2938 if (*map == 0) 2939 count = 0; 2940 kunmap_atomic(map); 2941 page = list_entry(page->lru.prev, struct page, lru); 2942 while (page != head) { 2943 map = kmap_atomic(page) + offset; 2944 *map = SWAP_CONT_MAX | count; 2945 count = COUNT_CONTINUED; 2946 kunmap_atomic(map); 2947 page = list_entry(page->lru.prev, struct page, lru); 2948 } 2949 return count == COUNT_CONTINUED; 2950 } 2951 } 2952 2953 /* 2954 * free_swap_count_continuations - swapoff free all the continuation pages 2955 * appended to the swap_map, after swap_map is quiesced, before vfree'ing it. 2956 */ 2957 static void free_swap_count_continuations(struct swap_info_struct *si) 2958 { 2959 pgoff_t offset; 2960 2961 for (offset = 0; offset < si->max; offset += PAGE_SIZE) { 2962 struct page *head; 2963 head = vmalloc_to_page(si->swap_map + offset); 2964 if (page_private(head)) { 2965 struct page *page, *next; 2966 2967 list_for_each_entry_safe(page, next, &head->lru, lru) { 2968 list_del(&page->lru); 2969 __free_page(page); 2970 } 2971 } 2972 } 2973 } 2974