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