mm/swapfile.c

   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/config.h>
   9 #include <linux/mm.h>
  10 #include <linux/hugetlb.h>
  11 #include <linux/mman.h>
  12 #include <linux/slab.h>
  13 #include <linux/kernel_stat.h>
  14 #include <linux/swap.h>
  15 #include <linux/vmalloc.h>
  16 #include <linux/pagemap.h>
  17 #include <linux/namei.h>
  18 #include <linux/shm.h>
  19 #include <linux/blkdev.h>
  20 #include <linux/writeback.h>
  21 #include <linux/proc_fs.h>
  22 #include <linux/seq_file.h>
  23 #include <linux/init.h>
  24 #include <linux/module.h>
  25 #include <linux/rmap.h>
  26 #include <linux/security.h>
  27 #include <linux/backing-dev.h>
  28
  29 #include <asm/pgtable.h>
  30 #include <asm/tlbflush.h>
  31 #include <linux/swapops.h>
  32
  33 spinlock_t swaplock = SPIN_LOCK_UNLOCKED;
  34 unsigned int nr_swapfiles;
  35 long total_swap_pages;
  36 static int swap_overflow;
  37
  38 EXPORT_SYMBOL(total_swap_pages);
  39
  40 static const char Bad_file[] = "Bad swap file entry ";
  41 static const char Unused_file[] = "Unused swap file entry ";
  42 static const char Bad_offset[] = "Bad swap offset entry ";
  43 static const char Unused_offset[] = "Unused swap offset entry ";
  44
  45 struct swap_list_t swap_list = {-1, -1};
  46
  47 struct swap_info_struct swap_info[MAX_SWAPFILES];
  48
  49 static DECLARE_MUTEX(swapon_sem);
  50
  51 /*
  52  * We need this because the bdev->unplug_fn can sleep and we cannot
  53  * hold swap_list_lock while calling the unplug_fn. And swap_list_lock
  54  * cannot be turned into a semaphore.
  55  */
  56 static DECLARE_RWSEM(swap_unplug_sem);
  57
  58 #define SWAPFILE_CLUSTER 256
  59
  60 void swap_unplug_io_fn(struct backing_dev_info *unused_bdi, struct page *page)
  61 {
  62         swp_entry_t entry;
  63
  64         down_read(&swap_unplug_sem);
  65         entry.val = page->private;
  66         if (PageSwapCache(page)) {
  67                 struct block_device *bdev = swap_info[swp_type(entry)].bdev;
  68                 struct backing_dev_info *bdi;
  69
  70                 /*
  71                  * If the page is removed from swapcache from under us (with a
  72                  * racy try_to_unuse/swapoff) we need an additional reference
  73                  * count to avoid reading garbage from page->private above. If
  74                  * the WARN_ON triggers during a swapoff it maybe the race
  75                  * condition and it's harmless. However if it triggers without
  76                  * swapoff it signals a problem.
  77                  */
  78                 WARN_ON(page_count(page) <= 1);
  79
  80                 bdi = bdev->bd_inode->i_mapping->backing_dev_info;
  81                 bdi->unplug_io_fn(bdi, page);
  82         }
  83         up_read(&swap_unplug_sem);
  84 }
  85
  86 static inline int scan_swap_map(struct swap_info_struct *si)
  87 {
  88         unsigned long offset;
  89         /*
  90          * We try to cluster swap pages by allocating them
  91          * sequentially in swap.  Once we've allocated
  92          * SWAPFILE_CLUSTER pages this way, however, we resort to
  93          * first-free allocation, starting a new cluster.  This
  94          * prevents us from scattering swap pages all over the entire
  95          * swap partition, so that we reduce overall disk seek times
  96          * between swap pages.  -- sct */
  97         if (si->cluster_nr) {
  98                 while (si->cluster_next <= si->highest_bit) {
  99                         offset = si->cluster_next++;
 100                         if (si->swap_map[offset])
 101                                 continue;
 102                         si->cluster_nr--;
 103                         goto got_page;
 104                 }
 105         }
 106         si->cluster_nr = SWAPFILE_CLUSTER;
 107
 108         /* try to find an empty (even not aligned) cluster. */
 109         offset = si->lowest_bit;
 110  check_next_cluster:
 111         if (offset+SWAPFILE_CLUSTER-1 <= si->highest_bit)
 112         {
 113                 unsigned long nr;
 114                 for (nr = offset; nr < offset+SWAPFILE_CLUSTER; nr++)
 115                         if (si->swap_map[nr])
 116                         {
 117                                 offset = nr+1;
 118                                 goto check_next_cluster;
 119                         }
 120                 /* We found a completly empty cluster, so start
 121                  * using it.
 122                  */
 123                 goto got_page;
 124         }
 125         /* No luck, so now go finegrined as usual. -Andrea */
 126         for (offset = si->lowest_bit; offset <= si->highest_bit ; offset++) {
 127                 if (si->swap_map[offset])
 128                         continue;
 129                 si->lowest_bit = offset+1;
 130         got_page:
 131                 if (offset == si->lowest_bit)
 132                         si->lowest_bit++;
 133                 if (offset == si->highest_bit)
 134                         si->highest_bit--;
 135                 if (si->lowest_bit > si->highest_bit) {
 136                         si->lowest_bit = si->max;
 137                         si->highest_bit = 0;
 138                 }
 139                 si->swap_map[offset] = 1;
 140                 si->inuse_pages++;
 141                 nr_swap_pages--;
 142                 si->cluster_next = offset+1;
 143                 return offset;
 144         }
 145         si->lowest_bit = si->max;
 146         si->highest_bit = 0;
 147         return 0;
 148 }
 149
 150 swp_entry_t get_swap_page(void)
 151 {
 152         struct swap_info_struct * p;
 153         unsigned long offset;
 154         swp_entry_t entry;
 155         int type, wrapped = 0;
 156
 157         entry.val = 0;  /* Out of memory */
 158         swap_list_lock();
 159         type = swap_list.next;
 160         if (type < 0)
 161                 goto out;
 162         if (nr_swap_pages <= 0)
 163                 goto out;
 164
 165         while (1) {
 166                 p = &swap_info[type];
 167                 if ((p->flags & SWP_ACTIVE) == SWP_ACTIVE) {
 168                         swap_device_lock(p);
 169                         offset = scan_swap_map(p);
 170                         swap_device_unlock(p);
 171                         if (offset) {
 172                                 entry = swp_entry(type,offset);
 173                                 type = swap_info[type].next;
 174                                 if (type < 0 ||
 175                                         p->prio != swap_info[type].prio) {
 176                                                 swap_list.next = swap_list.head;
 177                                 } else {
 178                                         swap_list.next = type;
 179                                 }
 180                                 goto out;
 181                         }
 182                 }
 183                 type = p->next;
 184                 if (!wrapped) {
 185                         if (type < 0 || p->prio != swap_info[type].prio) {
 186                                 type = swap_list.head;
 187                                 wrapped = 1;
 188                         }
 189                 } else
 190                         if (type < 0)
 191                                 goto out;       /* out of swap space */
 192         }
 193 out:
 194         swap_list_unlock();
 195         return entry;
 196 }
 197
 198 static struct swap_info_struct * swap_info_get(swp_entry_t entry)
 199 {
 200         struct swap_info_struct * p;
 201         unsigned long offset, type;
 202
 203         if (!entry.val)
 204                 goto out;
 205         type = swp_type(entry);
 206         if (type >= nr_swapfiles)
 207                 goto bad_nofile;
 208         p = & swap_info[type];
 209         if (!(p->flags & SWP_USED))
 210                 goto bad_device;
 211         offset = swp_offset(entry);
 212         if (offset >= p->max)
 213                 goto bad_offset;
 214         if (!p->swap_map[offset])
 215                 goto bad_free;
 216         swap_list_lock();
 217         if (p->prio > swap_info[swap_list.next].prio)
 218                 swap_list.next = type;
 219         swap_device_lock(p);
 220         return p;
 221
 222 bad_free:
 223         printk(KERN_ERR "swap_free: %s%08lx\n", Unused_offset, entry.val);
 224         goto out;
 225 bad_offset:
 226         printk(KERN_ERR "swap_free: %s%08lx\n", Bad_offset, entry.val);
 227         goto out;
 228 bad_device:
 229         printk(KERN_ERR "swap_free: %s%08lx\n", Unused_file, entry.val);
 230         goto out;
 231 bad_nofile:
 232         printk(KERN_ERR "swap_free: %s%08lx\n", Bad_file, entry.val);
 233 out:
 234         return NULL;
 235 }
 236
 237 static void swap_info_put(struct swap_info_struct * p)
 238 {
 239         swap_device_unlock(p);
 240         swap_list_unlock();
 241 }
 242
 243 static int swap_entry_free(struct swap_info_struct *p, unsigned long offset)
 244 {
 245         int count = p->swap_map[offset];
 246
 247         if (count < SWAP_MAP_MAX) {
 248                 count--;
 249                 p->swap_map[offset] = count;
 250                 if (!count) {
 251                         if (offset < p->lowest_bit)
 252                                 p->lowest_bit = offset;
 253                         if (offset > p->highest_bit)
 254                                 p->highest_bit = offset;
 255                         nr_swap_pages++;
 256                         p->inuse_pages--;
 257                 }
 258         }
 259         return count;
 260 }
 261
 262 /*
 263  * Caller has made sure that the swapdevice corresponding to entry
 264  * is still around or has not been recycled.
 265  */
 266 void swap_free(swp_entry_t entry)
 267 {
 268         struct swap_info_struct * p;
 269
 270         p = swap_info_get(entry);
 271         if (p) {
 272                 swap_entry_free(p, swp_offset(entry));
 273                 swap_info_put(p);
 274         }
 275 }
 276
 277 /*
 278  * Check if we're the only user of a swap page,
 279  * when the page is locked.
 280  */
 281 static int exclusive_swap_page(struct page *page)
 282 {
 283         int retval = 0;
 284         struct swap_info_struct * p;
 285         swp_entry_t entry;
 286
 287         entry.val = page->private;
 288         p = swap_info_get(entry);
 289         if (p) {
 290                 /* Is the only swap cache user the cache itself? */
 291                 if (p->swap_map[swp_offset(entry)] == 1) {
 292                         /* Recheck the page count with the swapcache lock held.. */
 293                         spin_lock_irq(&swapper_space.tree_lock);
 294                         if (page_count(page) == 2)
 295                                 retval = 1;
 296                         spin_unlock_irq(&swapper_space.tree_lock);
 297                 }
 298                 swap_info_put(p);
 299         }
 300         return retval;
 301 }
 302
 303 /*
 304  * We can use this swap cache entry directly
 305  * if there are no other references to it.
 306  *
 307  * Here "exclusive_swap_page()" does the real
 308  * work, but we opportunistically check whether
 309  * we need to get all the locks first..
 310  */
 311 int can_share_swap_page(struct page *page)
 312 {
 313         int retval = 0;
 314
 315         if (!PageLocked(page))
 316                 BUG();
 317         switch (page_count(page)) {
 318         case 3:
 319                 if (!PagePrivate(page))
 320                         break;
 321                 /* Fallthrough */
 322         case 2:
 323                 if (!PageSwapCache(page))
 324                         break;
 325                 retval = exclusive_swap_page(page);
 326                 break;
 327         case 1:
 328                 if (PageReserved(page))
 329                         break;
 330                 retval = 1;
 331         }
 332         return retval;
 333 }
 334
 335 /*
 336  * Work out if there are any other processes sharing this
 337  * swap cache page. Free it if you can. Return success.
 338  */
 339 int remove_exclusive_swap_page(struct page *page)
 340 {
 341         int retval;
 342         struct swap_info_struct * p;
 343         swp_entry_t entry;
 344
 345         BUG_ON(PagePrivate(page));
 346         BUG_ON(!PageLocked(page));
 347
 348         if (!PageSwapCache(page))
 349                 return 0;
 350         if (PageWriteback(page))
 351                 return 0;
 352         if (page_count(page) != 2) /* 2: us + cache */
 353                 return 0;
 354
 355         entry.val = page->private;
 356         p = swap_info_get(entry);
 357         if (!p)
 358                 return 0;
 359
 360         /* Is the only swap cache user the cache itself? */
 361         retval = 0;
 362         if (p->swap_map[swp_offset(entry)] == 1) {
 363                 /* Recheck the page count with the swapcache lock held.. */
 364                 spin_lock_irq(&swapper_space.tree_lock);
 365                 if ((page_count(page) == 2) && !PageWriteback(page)) {
 366                         __delete_from_swap_cache(page);
 367                         SetPageDirty(page);
 368                         retval = 1;
 369                 }
 370                 spin_unlock_irq(&swapper_space.tree_lock);
 371         }
 372         swap_info_put(p);
 373
 374         if (retval) {
 375                 swap_free(entry);
 376                 page_cache_release(page);
 377         }
 378
 379         return retval;
 380 }
 381
 382 /*
 383  * Free the swap entry like above, but also try to
 384  * free the page cache entry if it is the last user.
 385  */
 386 void free_swap_and_cache(swp_entry_t entry)
 387 {
 388         struct swap_info_struct * p;
 389         struct page *page = NULL;
 390
 391         p = swap_info_get(entry);
 392         if (p) {
 393                 if (swap_entry_free(p, swp_offset(entry)) == 1) {
 394                         spin_lock_irq(&swapper_space.tree_lock);
 395                         page = radix_tree_lookup(&swapper_space.page_tree,
 396                                 entry.val);
 397                         if (page && TestSetPageLocked(page))
 398                                 page = NULL;
 399                         spin_unlock_irq(&swapper_space.tree_lock);
 400                 }
 401                 swap_info_put(p);
 402         }
 403         if (page) {
 404                 int one_user;
 405
 406                 BUG_ON(PagePrivate(page));
 407                 page_cache_get(page);
 408                 one_user = (page_count(page) == 2);
 409                 /* Only cache user (+us), or swap space full? Free it! */
 410                 if (!PageWriteback(page) && (one_user || vm_swap_full())) {
 411                         delete_from_swap_cache(page);
 412                         SetPageDirty(page);
 413                 }
 414                 unlock_page(page);
 415                 page_cache_release(page);
 416         }
 417 }
 418
 419 /*
 420  * The swap entry has been read in advance, and we return 1 to indicate
 421  * that the page has been used or is no longer needed.
 422  *
 423  * Always set the resulting pte to be nowrite (the same as COW pages
 424  * after one process has exited).  We don't know just how many PTEs will
 425  * share this swap entry, so be cautious and let do_wp_page work out
 426  * what to do if a write is requested later.
 427  */
 428 /* vma->vm_mm->page_table_lock is held */
 429 static void
 430 unuse_pte(struct vm_area_struct *vma, unsigned long address, pte_t *dir,
 431         swp_entry_t entry, struct page *page)
 432 {
 433         vma->vm_mm->rss++;
 434         get_page(page);
 435         set_pte(dir, pte_mkold(mk_pte(page, vma->vm_page_prot)));
 436         page_add_anon_rmap(page, vma, address);
 437         swap_free(entry);
 438 }
 439
 440 /* vma->vm_mm->page_table_lock is held */
 441 static unsigned long unuse_pmd(struct vm_area_struct * vma, pmd_t *dir,
 442         unsigned long address, unsigned long size, unsigned long offset,
 443         swp_entry_t entry, struct page *page)
 444 {
 445         pte_t * pte;
 446         unsigned long end;
 447         pte_t swp_pte = swp_entry_to_pte(entry);
 448
 449         if (pmd_none(*dir))
 450                 return 0;
 451         if (pmd_bad(*dir)) {
 452                 pmd_ERROR(*dir);
 453                 pmd_clear(dir);
 454                 return 0;
 455         }
 456         pte = pte_offset_map(dir, address);
 457         offset += address & PMD_MASK;
 458         address &= ~PMD_MASK;
 459         end = address + size;
 460         if (end > PMD_SIZE)
 461                 end = PMD_SIZE;
 462         do {
 463                 /*
 464                  * swapoff spends a _lot_ of time in this loop!
 465                  * Test inline before going to call unuse_pte.
 466                  */
 467                 if (unlikely(pte_same(*pte, swp_pte))) {
 468                         unuse_pte(vma, offset + address, pte, entry, page);
 469                         pte_unmap(pte);
 470
 471                         /*
 472                          * Move the page to the active list so it is not
 473                          * immediately swapped out again after swapon.
 474                          */
 475                         activate_page(page);
 476
 477                         /* add 1 since address may be 0 */
 478                         return 1 + offset + address;
 479                 }
 480                 address += PAGE_SIZE;
 481                 pte++;
 482         } while (address && (address < end));
 483         pte_unmap(pte - 1);
 484         return 0;
 485 }
 486
 487 /* vma->vm_mm->page_table_lock is held */
 488 static unsigned long unuse_pgd(struct vm_area_struct * vma, pgd_t *dir,
 489         unsigned long address, unsigned long size,
 490         swp_entry_t entry, struct page *page)
 491 {
 492         pmd_t * pmd;
 493         unsigned long offset, end;
 494         unsigned long foundaddr;
 495
 496         if (pgd_none(*dir))
 497                 return 0;
 498         if (pgd_bad(*dir)) {
 499                 pgd_ERROR(*dir);
 500                 pgd_clear(dir);
 501                 return 0;
 502         }
 503         pmd = pmd_offset(dir, address);
 504         offset = address & PGDIR_MASK;
 505         address &= ~PGDIR_MASK;
 506         end = address + size;
 507         if (end > PGDIR_SIZE)
 508                 end = PGDIR_SIZE;
 509         if (address >= end)
 510                 BUG();
 511         do {
 512                 foundaddr = unuse_pmd(vma, pmd, address, end - address,
 513                                                 offset, entry, page);
 514                 if (foundaddr)
 515                         return foundaddr;
 516                 address = (address + PMD_SIZE) & PMD_MASK;
 517                 pmd++;
 518         } while (address && (address < end));
 519         return 0;
 520 }
 521
 522 /* vma->vm_mm->page_table_lock is held */
 523 static unsigned long unuse_vma(struct vm_area_struct * vma,
 524         swp_entry_t entry, struct page *page)
 525 {
 526         pgd_t *pgdir;
 527         unsigned long start, end;
 528         unsigned long foundaddr;
 529
 530         if (page->mapping) {
 531                 start = page_address_in_vma(page, vma);
 532                 if (start == -EFAULT)
 533                         return 0;
 534                 else
 535                         end = start + PAGE_SIZE;
 536         } else {
 537                 start = vma->vm_start;
 538                 end = vma->vm_end;
 539         }
 540         pgdir = pgd_offset(vma->vm_mm, start);
 541         do {
 542                 foundaddr = unuse_pgd(vma, pgdir, start, end - start,
 543                                                 entry, page);
 544                 if (foundaddr)
 545                         return foundaddr;
 546                 start = (start + PGDIR_SIZE) & PGDIR_MASK;
 547                 pgdir++;
 548         } while (start && (start < end));
 549         return 0;
 550 }
 551
 552 static int unuse_process(struct mm_struct * mm,
 553                         swp_entry_t entry, struct page* page)
 554 {
 555         struct vm_area_struct* vma;
 556         unsigned long foundaddr = 0;
 557
 558         /*
 559          * Go through process' page directory.
 560          */
 561         if (!down_read_trylock(&mm->mmap_sem)) {
 562                 /*
 563                  * Our reference to the page stops try_to_unmap_one from
 564                  * unmapping its ptes, so swapoff can make progress.
 565                  */
 566                 unlock_page(page);
 567                 down_read(&mm->mmap_sem);
 568                 lock_page(page);
 569         }
 570         spin_lock(&mm->page_table_lock);
 571         for (vma = mm->mmap; vma; vma = vma->vm_next) {
 572                 if (vma->anon_vma) {
 573                         foundaddr = unuse_vma(vma, entry, page);
 574                         if (foundaddr)
 575                                 break;
 576                 }
 577         }
 578         spin_unlock(&mm->page_table_lock);
 579         up_read(&mm->mmap_sem);
 580         /*
 581          * Currently unuse_process cannot fail, but leave error handling
 582          * at call sites for now, since we change it from time to time.
 583          */
 584         return 0;
 585 }
 586
 587 /*
 588  * Scan swap_map from current position to next entry still in use.
 589  * Recycle to start on reaching the end, returning 0 when empty.
 590  */
 591 static int find_next_to_unuse(struct swap_info_struct *si, int prev)
 592 {
 593         int max = si->max;
 594         int i = prev;
 595         int count;
 596
 597         /*
 598          * No need for swap_device_lock(si) here: we're just looking
 599          * for whether an entry is in use, not modifying it; false
 600          * hits are okay, and sys_swapoff() has already prevented new
 601          * allocations from this area (while holding swap_list_lock()).
 602          */
 603         for (;;) {
 604                 if (++i >= max) {
 605                         if (!prev) {
 606                                 i = 0;
 607                                 break;
 608                         }
 609                         /*
 610                          * No entries in use at top of swap_map,
 611                          * loop back to start and recheck there.
 612                          */
 613                         max = prev + 1;
 614                         prev = 0;
 615                         i = 1;
 616                 }
 617                 count = si->swap_map[i];
 618                 if (count && count != SWAP_MAP_BAD)
 619                         break;
 620         }
 621         return i;
 622 }
 623
 624 /*
 625  * We completely avoid races by reading each swap page in advance,
 626  * and then search for the process using it.  All the necessary
 627  * page table adjustments can then be made atomically.
 628  */
 629 static int try_to_unuse(unsigned int type)
 630 {
 631         struct swap_info_struct * si = &swap_info[type];
 632         struct mm_struct *start_mm;
 633         unsigned short *swap_map;
 634         unsigned short swcount;
 635         struct page *page;
 636         swp_entry_t entry;
 637         int i = 0;
 638         int retval = 0;
 639         int reset_overflow = 0;
 640         int shmem;
 641
 642         /*
 643          * When searching mms for an entry, a good strategy is to
 644          * start at the first mm we freed the previous entry from
 645          * (though actually we don't notice whether we or coincidence
 646          * freed the entry).  Initialize this start_mm with a hold.
 647          *
 648          * A simpler strategy would be to start at the last mm we
 649          * freed the previous entry from; but that would take less
 650          * advantage of mmlist ordering (now preserved by swap_out()),
 651          * which clusters forked address spaces together, most recent
 652          * child immediately after parent.  If we race with dup_mmap(),
 653          * we very much want to resolve parent before child, otherwise
 654          * we may miss some entries: using last mm would invert that.
 655          */
 656         start_mm = &init_mm;
 657         atomic_inc(&init_mm.mm_users);
 658
 659         /*
 660          * Keep on scanning until all entries have gone.  Usually,
 661          * one pass through swap_map is enough, but not necessarily:
 662          * mmput() removes mm from mmlist before exit_mmap() and its
 663          * zap_page_range().  That's not too bad, those entries are
 664          * on their way out, and handled faster there than here.
 665          * do_munmap() behaves similarly, taking the range out of mm's
 666          * vma list before zap_page_range().  But unfortunately, when
 667          * unmapping a part of a vma, it takes the whole out first,
 668          * then reinserts what's left after (might even reschedule if
 669          * open() method called) - so swap entries may be invisible
 670          * to swapoff for a while, then reappear - but that is rare.
 671          */
 672         while ((i = find_next_to_unuse(si, i)) != 0) {
 673                 if (signal_pending(current)) {
 674                         retval = -EINTR;
 675                         break;
 676                 }
 677
 678                 /*
 679                  * Get a page for the entry, using the existing swap
 680                  * cache page if there is one.  Otherwise, get a clean
 681                  * page and read the swap into it.
 682                  */
 683                 swap_map = &si->swap_map[i];
 684                 entry = swp_entry(type, i);
 685                 page = read_swap_cache_async(entry, NULL, 0);
 686                 if (!page) {
 687                         /*
 688                          * Either swap_duplicate() failed because entry
 689                          * has been freed independently, and will not be
 690                          * reused since sys_swapoff() already disabled
 691                          * allocation from here, or alloc_page() failed.
 692                          */
 693                         if (!*swap_map)
 694                                 continue;
 695                         retval = -ENOMEM;
 696                         break;
 697                 }
 698
 699                 /*
 700                  * Don't hold on to start_mm if it looks like exiting.
 701                  */
 702                 if (atomic_read(&start_mm->mm_users) == 1) {
 703                         mmput(start_mm);
 704                         start_mm = &init_mm;
 705                         atomic_inc(&init_mm.mm_users);
 706                 }
 707
 708                 /*
 709                  * Wait for and lock page.  When do_swap_page races with
 710                  * try_to_unuse, do_swap_page can handle the fault much
 711                  * faster than try_to_unuse can locate the entry.  This
 712                  * apparently redundant "wait_on_page_locked" lets try_to_unuse
 713                  * defer to do_swap_page in such a case - in some tests,
 714                  * do_swap_page and try_to_unuse repeatedly compete.
 715                  */
 716                 wait_on_page_locked(page);
 717                 wait_on_page_writeback(page);
 718                 lock_page(page);
 719                 wait_on_page_writeback(page);
 720
 721                 /*
 722                  * Remove all references to entry, without blocking.
 723                  * Whenever we reach init_mm, there's no address space
 724                  * to search, but use it as a reminder to search shmem.
 725                  */
 726                 shmem = 0;
 727                 swcount = *swap_map;
 728                 if (swcount > 1) {
 729                         if (start_mm == &init_mm)
 730                                 shmem = shmem_unuse(entry, page);
 731                         else
 732                                 retval = unuse_process(start_mm, entry, page);
 733                 }
 734                 if (*swap_map > 1) {
 735                         int set_start_mm = (*swap_map >= swcount);
 736                         struct list_head *p = &start_mm->mmlist;
 737                         struct mm_struct *new_start_mm = start_mm;
 738                         struct mm_struct *prev_mm = start_mm;
 739                         struct mm_struct *mm;
 740
 741                         atomic_inc(&new_start_mm->mm_users);
 742                         atomic_inc(&prev_mm->mm_users);
 743                         spin_lock(&mmlist_lock);
 744                         while (*swap_map > 1 && !retval &&
 745                                         (p = p->next) != &start_mm->mmlist) {
 746                                 mm = list_entry(p, struct mm_struct, mmlist);
 747                                 atomic_inc(&mm->mm_users);
 748                                 spin_unlock(&mmlist_lock);
 749                                 mmput(prev_mm);
 750                                 prev_mm = mm;
 751
 752                                 cond_resched();
 753
 754                                 swcount = *swap_map;
 755                                 if (swcount <= 1)
 756                                         ;
 757                                 else if (mm == &init_mm) {
 758                                         set_start_mm = 1;
 759                                         shmem = shmem_unuse(entry, page);
 760                                 } else
 761                                         retval = unuse_process(mm, entry, page);
 762                                 if (set_start_mm && *swap_map < swcount) {
 763                                         mmput(new_start_mm);
 764                                         atomic_inc(&mm->mm_users);
 765                                         new_start_mm = mm;
 766                                         set_start_mm = 0;
 767                                 }
 768                                 spin_lock(&mmlist_lock);
 769                         }
 770                         spin_unlock(&mmlist_lock);
 771                         mmput(prev_mm);
 772                         mmput(start_mm);
 773                         start_mm = new_start_mm;
 774                 }
 775                 if (retval) {
 776                         unlock_page(page);
 777                         page_cache_release(page);
 778                         break;
 779                 }
 780
 781                 /*
 782                  * How could swap count reach 0x7fff when the maximum
 783                  * pid is 0x7fff, and there's no way to repeat a swap
 784                  * page within an mm (except in shmem, where it's the
 785                  * shared object which takes the reference count)?
 786                  * We believe SWAP_MAP_MAX cannot occur in Linux 2.4.
 787                  *
 788                  * If that's wrong, then we should worry more about
 789                  * exit_mmap() and do_munmap() cases described above:
 790                  * we might be resetting SWAP_MAP_MAX too early here.
 791                  * We know "Undead"s can happen, they're okay, so don't
 792                  * report them; but do report if we reset SWAP_MAP_MAX.
 793                  */
 794                 if (*swap_map == SWAP_MAP_MAX) {
 795                         swap_device_lock(si);
 796                         *swap_map = 1;
 797                         swap_device_unlock(si);
 798                         reset_overflow = 1;
 799                 }
 800
 801                 /*
 802                  * If a reference remains (rare), we would like to leave
 803                  * the page in the swap cache; but try_to_unmap could
 804                  * then re-duplicate the entry once we drop page lock,
 805                  * so we might loop indefinitely; also, that page could
 806                  * not be swapped out to other storage meanwhile.  So:
 807                  * delete from cache even if there's another reference,
 808                  * after ensuring that the data has been saved to disk -
 809                  * since if the reference remains (rarer), it will be
 810                  * read from disk into another page.  Splitting into two
 811                  * pages would be incorrect if swap supported "shared
 812                  * private" pages, but they are handled by tmpfs files.
 813                  *
 814                  * Note shmem_unuse already deleted a swappage from
 815                  * the swap cache, unless the move to filepage failed:
 816                  * in which case it left swappage in cache, lowered its
 817                  * swap count to pass quickly through the loops above,
 818                  * and now we must reincrement count to try again later.
 819                  */
 820                 if ((*swap_map > 1) && PageDirty(page) && PageSwapCache(page)) {
 821                         struct writeback_control wbc = {
 822                                 .sync_mode = WB_SYNC_NONE,
 823                         };
 824
 825                         swap_writepage(page, &wbc);
 826                         lock_page(page);
 827                         wait_on_page_writeback(page);
 828                 }
 829                 if (PageSwapCache(page)) {
 830                         if (shmem)
 831                                 swap_duplicate(entry);
 832                         else
 833                                 delete_from_swap_cache(page);
 834                 }
 835
 836                 /*
 837                  * So we could skip searching mms once swap count went
 838                  * to 1, we did not mark any present ptes as dirty: must
 839                  * mark page dirty so shrink_list will preserve it.
 840                  */
 841                 SetPageDirty(page);
 842                 unlock_page(page);
 843                 page_cache_release(page);
 844
 845                 /*
 846                  * Make sure that we aren't completely killing
 847                  * interactive performance.
 848                  */
 849                 cond_resched();
 850         }
 851
 852         mmput(start_mm);
 853         if (reset_overflow) {
 854                 printk(KERN_WARNING "swapoff: cleared swap entry overflow\n");
 855                 swap_overflow = 0;
 856         }
 857         return retval;
 858 }
 859
 860 /*
 861  * Use this swapdev's extent info to locate the (PAGE_SIZE) block which
 862  * corresponds to page offset `offset'.
 863  */
 864 sector_t map_swap_page(struct swap_info_struct *sis, pgoff_t offset)
 865 {
 866         struct swap_extent *se = sis->curr_swap_extent;
 867         struct swap_extent *start_se = se;
 868
 869         for ( ; ; ) {
 870                 struct list_head *lh;
 871
 872                 if (se->start_page <= offset &&
 873                                 offset < (se->start_page + se->nr_pages)) {
 874                         return se->start_block + (offset - se->start_page);
 875                 }
 876                 lh = se->list.prev;
 877                 if (lh == &sis->extent_list)
 878                         lh = lh->prev;
 879                 se = list_entry(lh, struct swap_extent, list);
 880                 sis->curr_swap_extent = se;
 881                 BUG_ON(se == start_se);         /* It *must* be present */
 882         }
 883 }
 884
 885 /*
 886  * Free all of a swapdev's extent information
 887  */
 888 static void destroy_swap_extents(struct swap_info_struct *sis)
 889 {
 890         while (!list_empty(&sis->extent_list)) {
 891                 struct swap_extent *se;
 892
 893                 se = list_entry(sis->extent_list.next,
 894                                 struct swap_extent, list);
 895                 list_del(&se->list);
 896                 kfree(se);
 897         }
 898         sis->nr_extents = 0;
 899 }
 900
 901 /*
 902  * Add a block range (and the corresponding page range) into this swapdev's
 903  * extent list.  The extent list is kept sorted in block order.
 904  *
 905  * This function rather assumes that it is called in ascending sector_t order.
 906  * It doesn't look for extent coalescing opportunities.
 907  */
 908 static int
 909 add_swap_extent(struct swap_info_struct *sis, unsigned long start_page,
 910                 unsigned long nr_pages, sector_t start_block)
 911 {
 912         struct swap_extent *se;
 913         struct swap_extent *new_se;
 914         struct list_head *lh;
 915
 916         lh = sis->extent_list.next;     /* The highest-addressed block */
 917         while (lh != &sis->extent_list) {
 918                 se = list_entry(lh, struct swap_extent, list);
 919                 if (se->start_block + se->nr_pages == start_block &&
 920                     se->start_page  + se->nr_pages == start_page) {
 921                         /* Merge it */
 922                         se->nr_pages += nr_pages;
 923                         return 0;
 924                 }
 925                 lh = lh->next;
 926         }
 927
 928         /*
 929          * No merge.  Insert a new extent, preserving ordering.
 930          */
 931         new_se = kmalloc(sizeof(*se), GFP_KERNEL);
 932         if (new_se == NULL)
 933                 return -ENOMEM;
 934         new_se->start_page = start_page;
 935         new_se->nr_pages = nr_pages;
 936         new_se->start_block = start_block;
 937
 938         lh = sis->extent_list.prev;     /* The lowest block */
 939         while (lh != &sis->extent_list) {
 940                 se = list_entry(lh, struct swap_extent, list);
 941                 if (se->start_block > start_block)
 942                         break;
 943                 lh = lh->prev;
 944         }
 945         list_add_tail(&new_se->list, lh);
 946         sis->nr_extents++;
 947         return 0;
 948 }
 949
 950 /*
 951  * A `swap extent' is a simple thing which maps a contiguous range of pages
 952  * onto a contiguous range of disk blocks.  An ordered list of swap extents
 953  * is built at swapon time and is then used at swap_writepage/swap_readpage
 954  * time for locating where on disk a page belongs.
 955  *
 956  * If the swapfile is an S_ISBLK block device, a single extent is installed.
 957  * This is done so that the main operating code can treat S_ISBLK and S_ISREG
 958  * swap files identically.
 959  *
 960  * Whether the swapdev is an S_ISREG file or an S_ISBLK blockdev, the swap
 961  * extent list operates in PAGE_SIZE disk blocks.  Both S_ISREG and S_ISBLK
 962  * swapfiles are handled *identically* after swapon time.
 963  *
 964  * For S_ISREG swapfiles, setup_swap_extents() will walk all the file's blocks
 965  * and will parse them into an ordered extent list, in PAGE_SIZE chunks.  If
 966  * some stray blocks are found which do not fall within the PAGE_SIZE alignment
 967  * requirements, they are simply tossed out - we will never use those blocks
 968  * for swapping.
 969  *
 970  * For S_ISREG swapfiles we hold i_sem across the life of the swapon.  This
 971  * prevents root from shooting her foot off by ftruncating an in-use swapfile,
 972  * which will scribble on the fs.
 973  *
 974  * The amount of disk space which a single swap extent represents varies.
 975  * Typically it is in the 1-4 megabyte range.  So we can have hundreds of
 976  * extents in the list.  To avoid much list walking, we cache the previous
 977  * search location in `curr_swap_extent', and start new searches from there.
 978  * This is extremely effective.  The average number of iterations in
 979  * map_swap_page() has been measured at about 0.3 per page.  - akpm.
 980  */
 981 static int setup_swap_extents(struct swap_info_struct *sis)
 982 {
 983         struct inode *inode;
 984         unsigned blocks_per_page;
 985         unsigned long page_no;
 986         unsigned blkbits;
 987         sector_t probe_block;
 988         sector_t last_block;
 989         int ret;
 990
 991         inode = sis->swap_file->f_mapping->host;
 992         if (S_ISBLK(inode->i_mode)) {
 993                 ret = add_swap_extent(sis, 0, sis->max, 0);
 994                 goto done;
 995         }
 996
 997         blkbits = inode->i_blkbits;
 998         blocks_per_page = PAGE_SIZE >> blkbits;
 999
1000         /*
1001          * Map all the blocks into the extent list.  This code doesn't try
1002          * to be very smart.
1003          */
1004         probe_block = 0;
1005         page_no = 0;
1006         last_block = i_size_read(inode) >> blkbits;
1007         while ((probe_block + blocks_per_page) <= last_block &&
1008                         page_no < sis->max) {
1009                 unsigned block_in_page;
1010                 sector_t first_block;
1011
1012                 first_block = bmap(inode, probe_block);
1013                 if (first_block == 0)
1014                         goto bad_bmap;
1015
1016                 /*
1017                  * It must be PAGE_SIZE aligned on-disk
1018                  */
1019                 if (first_block & (blocks_per_page - 1)) {
1020                         probe_block++;
1021                         goto reprobe;
1022                 }
1023
1024                 for (block_in_page = 1; block_in_page < blocks_per_page;
1025                                         block_in_page++) {
1026                         sector_t block;
1027
1028                         block = bmap(inode, probe_block + block_in_page);
1029                         if (block == 0)
1030                                 goto bad_bmap;
1031                         if (block != first_block + block_in_page) {
1032                                 /* Discontiguity */
1033                                 probe_block++;
1034                                 goto reprobe;
1035                         }
1036                 }
1037
1038                 /*
1039                  * We found a PAGE_SIZE-length, PAGE_SIZE-aligned run of blocks
1040                  */
1041                 ret = add_swap_extent(sis, page_no, 1,
1042                                 first_block >> (PAGE_SHIFT - blkbits));
1043                 if (ret)
1044                         goto out;
1045                 page_no++;
1046                 probe_block += blocks_per_page;
1047 reprobe:
1048                 continue;
1049         }
1050         ret = 0;
1051         if (page_no == 0)
1052                 ret = -EINVAL;
1053         sis->max = page_no;
1054         sis->highest_bit = page_no - 1;
1055 done:
1056         sis->curr_swap_extent = list_entry(sis->extent_list.prev,
1057                                         struct swap_extent, list);
1058         goto out;
1059 bad_bmap:
1060         printk(KERN_ERR "swapon: swapfile has holes\n");
1061         ret = -EINVAL;
1062 out:
1063         return ret;
1064 }
1065
1066 #if 0   /* We don't need this yet */
1067 #include <linux/backing-dev.h>
1068 int page_queue_congested(struct page *page)
1069 {
1070         struct backing_dev_info *bdi;
1071
1072         BUG_ON(!PageLocked(page));      /* It pins the swap_info_struct */
1073
1074         if (PageSwapCache(page)) {
1075                 swp_entry_t entry = { .val = page->private };
1076                 struct swap_info_struct *sis;
1077
1078                 sis = get_swap_info_struct(swp_type(entry));
1079                 bdi = sis->bdev->bd_inode->i_mapping->backing_dev_info;
1080         } else
1081                 bdi = page->mapping->backing_dev_info;
1082         return bdi_write_congested(bdi);
1083 }
1084 #endif
1085
1086 asmlinkage long sys_swapoff(const char __user * specialfile)
1087 {
1088         struct swap_info_struct * p = NULL;
1089         unsigned short *swap_map;
1090         struct file *swap_file, *victim;
1091         struct address_space *mapping;
1092         struct inode *inode;
1093         char * pathname;
1094         int i, type, prev;
1095         int err;
1096
1097         if (!capable(CAP_SYS_ADMIN))
1098                 return -EPERM;
1099
1100         pathname = getname(specialfile);
1101         err = PTR_ERR(pathname);
1102         if (IS_ERR(pathname))
1103                 goto out;
1104
1105         victim = filp_open(pathname, O_RDWR|O_LARGEFILE, 0);
1106         putname(pathname);
1107         err = PTR_ERR(victim);
1108         if (IS_ERR(victim))
1109                 goto out;
1110
1111         mapping = victim->f_mapping;
1112         prev = -1;
1113         swap_list_lock();
1114         for (type = swap_list.head; type >= 0; type = swap_info[type].next) {
1115                 p = swap_info + type;
1116                 if ((p->flags & SWP_ACTIVE) == SWP_ACTIVE) {
1117                         if (p->swap_file->f_mapping == mapping)
1118                                 break;
1119                 }
1120                 prev = type;
1121         }
1122         if (type < 0) {
1123                 err = -EINVAL;
1124                 swap_list_unlock();
1125                 goto out_dput;
1126         }
1127         if (!security_vm_enough_memory(p->pages))
1128                 vm_unacct_memory(p->pages);
1129         else {
1130                 err = -ENOMEM;
1131                 swap_list_unlock();
1132                 goto out_dput;
1133         }
1134         if (prev < 0) {
1135                 swap_list.head = p->next;
1136         } else {
1137                 swap_info[prev].next = p->next;
1138         }
1139         if (type == swap_list.next) {
1140                 /* just pick something that's safe... */
1141                 swap_list.next = swap_list.head;
1142         }
1143         nr_swap_pages -= p->pages;
1144         total_swap_pages -= p->pages;
1145         p->flags &= ~SWP_WRITEOK;
1146         swap_list_unlock();
1147         current->flags |= PF_SWAPOFF;
1148         err = try_to_unuse(type);
1149         current->flags &= ~PF_SWAPOFF;
1150
1151         /* wait for any unplug function to finish */
1152         down_write(&swap_unplug_sem);
1153         up_write(&swap_unplug_sem);
1154
1155         if (err) {
1156                 /* re-insert swap space back into swap_list */
1157                 swap_list_lock();
1158                 for (prev = -1, i = swap_list.head; i >= 0; prev = i, i = swap_info[i].next)
1159                         if (p->prio >= swap_info[i].prio)
1160                                 break;
1161                 p->next = i;
1162                 if (prev < 0)
1163                         swap_list.head = swap_list.next = p - swap_info;
1164                 else
1165                         swap_info[prev].next = p - swap_info;
1166                 nr_swap_pages += p->pages;
1167                 total_swap_pages += p->pages;
1168                 p->flags |= SWP_WRITEOK;
1169                 swap_list_unlock();
1170                 goto out_dput;
1171         }
1172         down(&swapon_sem);
1173         swap_list_lock();
1174         swap_device_lock(p);
1175         swap_file = p->swap_file;
1176         p->swap_file = NULL;
1177         p->max = 0;
1178         swap_map = p->swap_map;
1179         p->swap_map = NULL;
1180         p->flags = 0;
1181         destroy_swap_extents(p);
1182         swap_device_unlock(p);
1183         swap_list_unlock();
1184         up(&swapon_sem);
1185         vfree(swap_map);
1186         inode = mapping->host;
1187         if (S_ISBLK(inode->i_mode)) {
1188                 struct block_device *bdev = I_BDEV(inode);
1189                 set_blocksize(bdev, p->old_block_size);
1190                 bd_release(bdev);
1191         } else {
1192                 down(&inode->i_sem);
1193                 inode->i_flags &= ~S_SWAPFILE;
1194                 up(&inode->i_sem);
1195         }
1196         filp_close(swap_file, NULL);
1197         err = 0;
1198
1199 out_dput:
1200         filp_close(victim, NULL);
1201 out:
1202         return err;
1203 }
1204
1205 #ifdef CONFIG_PROC_FS
1206 /* iterator */
1207 static void *swap_start(struct seq_file *swap, loff_t *pos)
1208 {
1209         struct swap_info_struct *ptr = swap_info;
1210         int i;
1211         loff_t l = *pos;
1212
1213         down(&swapon_sem);
1214
1215         for (i = 0; i < nr_swapfiles; i++, ptr++) {
1216                 if (!(ptr->flags & SWP_USED) || !ptr->swap_map)
1217                         continue;
1218                 if (!l--)
1219                         return ptr;
1220         }
1221
1222         return NULL;
1223 }
1224
1225 static void *swap_next(struct seq_file *swap, void *v, loff_t *pos)
1226 {
1227         struct swap_info_struct *ptr = v;
1228         struct swap_info_struct *endptr = swap_info + nr_swapfiles;
1229
1230         for (++ptr; ptr < endptr; ptr++) {
1231                 if (!(ptr->flags & SWP_USED) || !ptr->swap_map)
1232                         continue;
1233                 ++*pos;
1234                 return ptr;
1235         }
1236
1237         return NULL;
1238 }
1239
1240 static void swap_stop(struct seq_file *swap, void *v)
1241 {
1242         up(&swapon_sem);
1243 }
1244
1245 static int swap_show(struct seq_file *swap, void *v)
1246 {
1247         struct swap_info_struct *ptr = v;
1248         struct file *file;
1249         int len;
1250
1251         if (v == swap_info)
1252                 seq_puts(swap, "Filename\t\t\t\tType\t\tSize\tUsed\tPriority\n");
1253
1254         file = ptr->swap_file;
1255         len = seq_path(swap, file->f_vfsmnt, file->f_dentry, " \t\n\\");
1256         seq_printf(swap, "%*s%s\t%d\t%ld\t%d\n",
1257                        len < 40 ? 40 - len : 1, " ",
1258                        S_ISBLK(file->f_dentry->d_inode->i_mode) ?
1259                                 "partition" : "file\t",
1260                        ptr->pages << (PAGE_SHIFT - 10),
1261                        ptr->inuse_pages << (PAGE_SHIFT - 10),
1262                        ptr->prio);
1263         return 0;
1264 }
1265
1266 static struct seq_operations swaps_op = {
1267         .start =        swap_start,
1268         .next =         swap_next,
1269         .stop =         swap_stop,
1270         .show =         swap_show
1271 };
1272
1273 static int swaps_open(struct inode *inode, struct file *file)
1274 {
1275         return seq_open(file, &swaps_op);
1276 }
1277
1278 static struct file_operations proc_swaps_operations = {
1279         .open           = swaps_open,
1280         .read           = seq_read,
1281         .llseek         = seq_lseek,
1282         .release        = seq_release,
1283 };
1284
1285 static int __init procswaps_init(void)
1286 {
1287         struct proc_dir_entry *entry;
1288
1289         entry = create_proc_entry("swaps", 0, NULL);
1290         if (entry)
1291                 entry->proc_fops = &proc_swaps_operations;
1292         return 0;
1293 }
1294 __initcall(procswaps_init);
1295 #endif /* CONFIG_PROC_FS */
1296
1297 /*
1298  * Written 01/25/92 by Simmule Turner, heavily changed by Linus.
1299  *
1300  * The swapon system call
1301  */
1302 asmlinkage long sys_swapon(const char __user * specialfile, int swap_flags)
1303 {
1304         struct swap_info_struct * p;
1305         char *name = NULL;
1306         struct block_device *bdev = NULL;
1307         struct file *swap_file = NULL;
1308         struct address_space *mapping;
1309         unsigned int type;
1310         int i, prev;
1311         int error;
1312         static int least_priority;
1313         union swap_header *swap_header = NULL;
1314         int swap_header_version;
1315         int nr_good_pages = 0;
1316         unsigned long maxpages = 1;
1317         int swapfilesize;
1318         unsigned short *swap_map;
1319         struct page *page = NULL;
1320         struct inode *inode = NULL;
1321         int did_down = 0;
1322
1323         if (!capable(CAP_SYS_ADMIN))
1324                 return -EPERM;
1325         swap_list_lock();
1326         p = swap_info;
1327         for (type = 0 ; type < nr_swapfiles ; type++,p++)
1328                 if (!(p->flags & SWP_USED))
1329                         break;
1330         error = -EPERM;
1331         /*
1332          * Test if adding another swap device is possible. There are
1333          * two limiting factors: 1) the number of bits for the swap
1334          * type swp_entry_t definition and 2) the number of bits for
1335          * the swap type in the swap ptes as defined by the different
1336          * architectures. To honor both limitations a swap entry
1337          * with swap offset 0 and swap type ~0UL is created, encoded
1338          * to a swap pte, decoded to a swp_entry_t again and finally
1339          * the swap type part is extracted. This will mask all bits
1340          * from the initial ~0UL that can't be encoded in either the
1341          * swp_entry_t or the architecture definition of a swap pte.
1342          */
1343         if (type > swp_type(pte_to_swp_entry(swp_entry_to_pte(swp_entry(~0UL,0))))) {
1344                 swap_list_unlock();
1345                 goto out;
1346         }
1347         if (type >= nr_swapfiles)
1348                 nr_swapfiles = type+1;
1349         INIT_LIST_HEAD(&p->extent_list);
1350         p->flags = SWP_USED;
1351         p->nr_extents = 0;
1352         p->swap_file = NULL;
1353         p->old_block_size = 0;
1354         p->swap_map = NULL;
1355         p->lowest_bit = 0;
1356         p->highest_bit = 0;
1357         p->cluster_nr = 0;
1358         p->inuse_pages = 0;
1359         p->sdev_lock = SPIN_LOCK_UNLOCKED;
1360         p->next = -1;
1361         if (swap_flags & SWAP_FLAG_PREFER) {
1362                 p->prio =
1363                   (swap_flags & SWAP_FLAG_PRIO_MASK)>>SWAP_FLAG_PRIO_SHIFT;
1364         } else {
1365                 p->prio = --least_priority;
1366         }
1367         swap_list_unlock();
1368         name = getname(specialfile);
1369         error = PTR_ERR(name);
1370         if (IS_ERR(name)) {
1371                 name = NULL;
1372                 goto bad_swap_2;
1373         }
1374         swap_file = filp_open(name, O_RDWR|O_LARGEFILE, 0);
1375         error = PTR_ERR(swap_file);
1376         if (IS_ERR(swap_file)) {
1377                 swap_file = NULL;
1378                 goto bad_swap_2;
1379         }
1380
1381         p->swap_file = swap_file;
1382         mapping = swap_file->f_mapping;
1383         inode = mapping->host;
1384
1385         error = -EBUSY;
1386         for (i = 0; i < nr_swapfiles; i++) {
1387                 struct swap_info_struct *q = &swap_info[i];
1388
1389                 if (i == type || !q->swap_file)
1390                         continue;
1391                 if (mapping == q->swap_file->f_mapping)
1392                         goto bad_swap;
1393         }
1394
1395         error = -EINVAL;
1396         if (S_ISBLK(inode->i_mode)) {
1397                 bdev = I_BDEV(inode);
1398                 error = bd_claim(bdev, sys_swapon);
1399                 if (error < 0) {
1400                         bdev = NULL;
1401                         goto bad_swap;
1402                 }
1403                 p->old_block_size = block_size(bdev);
1404                 error = set_blocksize(bdev, PAGE_SIZE);
1405                 if (error < 0)
1406                         goto bad_swap;
1407                 p->bdev = bdev;
1408         } else if (S_ISREG(inode->i_mode)) {
1409                 p->bdev = inode->i_sb->s_bdev;
1410                 down(&inode->i_sem);
1411                 did_down = 1;
1412                 if (IS_SWAPFILE(inode)) {
1413                         error = -EBUSY;
1414                         goto bad_swap;
1415                 }
1416         } else {
1417                 goto bad_swap;
1418         }
1419
1420         swapfilesize = i_size_read(inode) >> PAGE_SHIFT;
1421
1422         /*
1423          * Read the swap header.
1424          */
1425         if (!mapping->a_ops->readpage) {
1426                 error = -EINVAL;
1427                 goto bad_swap;
1428         }
1429         page = read_cache_page(mapping, 0,
1430                         (filler_t *)mapping->a_ops->readpage, swap_file);
1431         if (IS_ERR(page)) {
1432                 error = PTR_ERR(page);
1433                 goto bad_swap;
1434         }
1435         wait_on_page_locked(page);
1436         if (!PageUptodate(page))
1437                 goto bad_swap;
1438         kmap(page);
1439         swap_header = page_address(page);
1440
1441         if (!memcmp("SWAP-SPACE",swap_header->magic.magic,10))
1442                 swap_header_version = 1;
1443         else if (!memcmp("SWAPSPACE2",swap_header->magic.magic,10))
1444                 swap_header_version = 2;
1445         else {
1446                 printk("Unable to find swap-space signature\n");
1447                 error = -EINVAL;
1448                 goto bad_swap;
1449         }
1450
1451         switch (swap_header_version) {
1452         case 1:
1453                 printk(KERN_ERR "version 0 swap is no longer supported. "
1454                         "Use mkswap -v1 %s\n", name);
1455                 error = -EINVAL;
1456                 goto bad_swap;
1457         case 2:
1458                 /* Check the swap header's sub-version and the size of
1459                    the swap file and bad block lists */
1460                 if (swap_header->info.version != 1) {
1461                         printk(KERN_WARNING
1462                                "Unable to handle swap header version %d\n",
1463                                swap_header->info.version);
1464                         error = -EINVAL;
1465                         goto bad_swap;
1466                 }
1467
1468                 p->lowest_bit  = 1;
1469                 /*
1470                  * Find out how many pages are allowed for a single swap
1471                  * device. There are two limiting factors: 1) the number of
1472                  * bits for the swap offset in the swp_entry_t type and
1473                  * 2) the number of bits in the a swap pte as defined by
1474                  * the different architectures. In order to find the
1475                  * largest possible bit mask a swap entry with swap type 0
1476                  * and swap offset ~0UL is created, encoded to a swap pte,
1477                  * decoded to a swp_entry_t again and finally the swap
1478                  * offset is extracted. This will mask all the bits from
1479                  * the initial ~0UL mask that can't be encoded in either
1480                  * the swp_entry_t or the architecture definition of a
1481                  * swap pte.
1482                  */
1483                 maxpages = swp_offset(pte_to_swp_entry(swp_entry_to_pte(swp_entry(0,~0UL)))) - 1;
1484                 if (maxpages > swap_header->info.last_page)
1485                         maxpages = swap_header->info.last_page;
1486                 p->highest_bit = maxpages - 1;
1487
1488                 error = -EINVAL;
1489                 if (swap_header->info.nr_badpages > MAX_SWAP_BADPAGES)
1490                         goto bad_swap;
1491
1492                 /* OK, set up the swap map and apply the bad block list */
1493                 if (!(p->swap_map = vmalloc(maxpages * sizeof(short)))) {
1494                         error = -ENOMEM;
1495                         goto bad_swap;
1496                 }
1497
1498                 error = 0;
1499                 memset(p->swap_map, 0, maxpages * sizeof(short));
1500                 for (i=0; i<swap_header->info.nr_badpages; i++) {
1501                         int page = swap_header->info.badpages[i];
1502                         if (page <= 0 || page >= swap_header->info.last_page)
1503                                 error = -EINVAL;
1504                         else
1505                                 p->swap_map[page] = SWAP_MAP_BAD;
1506                 }
1507                 nr_good_pages = swap_header->info.last_page -
1508                                 swap_header->info.nr_badpages -
1509                                 1 /* header page */;
1510                 if (error)
1511                         goto bad_swap;
1512         }
1513
1514         if (swapfilesize && maxpages > swapfilesize) {
1515                 printk(KERN_WARNING
1516                        "Swap area shorter than signature indicates\n");
1517                 error = -EINVAL;
1518                 goto bad_swap;
1519         }
1520         if (!nr_good_pages) {
1521                 printk(KERN_WARNING "Empty swap-file\n");
1522                 error = -EINVAL;
1523                 goto bad_swap;
1524         }
1525         p->swap_map[0] = SWAP_MAP_BAD;
1526         p->max = maxpages;
1527         p->pages = nr_good_pages;
1528
1529         error = setup_swap_extents(p);
1530         if (error)
1531                 goto bad_swap;
1532
1533         down(&swapon_sem);
1534         swap_list_lock();
1535         swap_device_lock(p);
1536         p->flags = SWP_ACTIVE;
1537         nr_swap_pages += nr_good_pages;
1538         total_swap_pages += nr_good_pages;
1539         printk(KERN_INFO "Adding %dk swap on %s.  Priority:%d extents:%d\n",
1540                 nr_good_pages<<(PAGE_SHIFT-10), name,
1541                 p->prio, p->nr_extents);
1542
1543         /* insert swap space into swap_list: */
1544         prev = -1;
1545         for (i = swap_list.head; i >= 0; i = swap_info[i].next) {
1546                 if (p->prio >= swap_info[i].prio) {
1547                         break;
1548                 }
1549                 prev = i;
1550         }
1551         p->next = i;
1552         if (prev < 0) {
1553                 swap_list.head = swap_list.next = p - swap_info;
1554         } else {
1555                 swap_info[prev].next = p - swap_info;
1556         }
1557         swap_device_unlock(p);
1558         swap_list_unlock();
1559         up(&swapon_sem);
1560         error = 0;
1561         goto out;
1562 bad_swap:
1563         if (bdev) {
1564                 set_blocksize(bdev, p->old_block_size);
1565                 bd_release(bdev);
1566         }
1567 bad_swap_2:
1568         swap_list_lock();
1569         swap_map = p->swap_map;
1570         p->swap_file = NULL;
1571         p->swap_map = NULL;
1572         p->flags = 0;
1573         if (!(swap_flags & SWAP_FLAG_PREFER))
1574                 ++least_priority;
1575         swap_list_unlock();
1576         destroy_swap_extents(p);
1577         if (swap_map)
1578                 vfree(swap_map);
1579         if (swap_file)
1580                 filp_close(swap_file, NULL);
1581 out:
1582         if (page && !IS_ERR(page)) {
1583                 kunmap(page);
1584                 page_cache_release(page);
1585         }
1586         if (name)
1587                 putname(name);
1588         if (did_down) {
1589                 if (!error)
1590                         inode->i_flags |= S_SWAPFILE;
1591                 up(&inode->i_sem);
1592         }
1593         return error;
1594 }
1595
1596 void si_swapinfo(struct sysinfo *val)
1597 {
1598         unsigned int i;
1599         unsigned long nr_to_be_unused = 0;
1600
1601         swap_list_lock();
1602         for (i = 0; i < nr_swapfiles; i++) {
1603                 if (!(swap_info[i].flags & SWP_USED) ||
1604                      (swap_info[i].flags & SWP_WRITEOK))
1605                         continue;
1606                 nr_to_be_unused += swap_info[i].inuse_pages;
1607         }
1608         val->freeswap = nr_swap_pages + nr_to_be_unused;
1609         val->totalswap = total_swap_pages + nr_to_be_unused;
1610         swap_list_unlock();
1611 }
1612
1613 /*
1614  * Verify that a swap entry is valid and increment its swap map count.
1615  *
1616  * Note: if swap_map[] reaches SWAP_MAP_MAX the entries are treated as
1617  * "permanent", but will be reclaimed by the next swapoff.
1618  */
1619 int swap_duplicate(swp_entry_t entry)
1620 {
1621         struct swap_info_struct * p;
1622         unsigned long offset, type;
1623         int result = 0;
1624
1625         type = swp_type(entry);
1626         if (type >= nr_swapfiles)
1627                 goto bad_file;
1628         p = type + swap_info;
1629         offset = swp_offset(entry);
1630
1631         swap_device_lock(p);
1632         if (offset < p->max && p->swap_map[offset]) {
1633                 if (p->swap_map[offset] < SWAP_MAP_MAX - 1) {
1634                         p->swap_map[offset]++;
1635                         result = 1;
1636                 } else if (p->swap_map[offset] <= SWAP_MAP_MAX) {
1637                         if (swap_overflow++ < 5)
1638                                 printk(KERN_WARNING "swap_dup: swap entry overflow\n");
1639                         p->swap_map[offset] = SWAP_MAP_MAX;
1640                         result = 1;
1641                 }
1642         }
1643         swap_device_unlock(p);
1644 out:
1645         return result;
1646
1647 bad_file:
1648         printk(KERN_ERR "swap_dup: %s%08lx\n", Bad_file, entry.val);
1649         goto out;
1650 }
1651
1652 struct swap_info_struct *
1653 get_swap_info_struct(unsigned type)
1654 {
1655         return &swap_info[type];
1656 }
1657
1658 /*
1659  * swap_device_lock prevents swap_map being freed. Don't grab an extra
1660  * reference on the swaphandle, it doesn't matter if it becomes unused.
1661  */
1662 int valid_swaphandles(swp_entry_t entry, unsigned long *offset)
1663 {
1664         int ret = 0, i = 1 << page_cluster;
1665         unsigned long toff;
1666         struct swap_info_struct *swapdev = swp_type(entry) + swap_info;
1667
1668         if (!page_cluster)      /* no readahead */
1669                 return 0;
1670         toff = (swp_offset(entry) >> page_cluster) << page_cluster;
1671         if (!toff)              /* first page is swap header */
1672                 toff++, i--;
1673         *offset = toff;
1674
1675         swap_device_lock(swapdev);
1676         do {
1677                 /* Don't read-ahead past the end of the swap area */
1678                 if (toff >= swapdev->max)
1679                         break;
1680                 /* Don't read in free or bad pages */
1681                 if (!swapdev->swap_map[toff])
1682                         break;
1683                 if (swapdev->swap_map[toff] == SWAP_MAP_BAD)
1684                         break;
1685                 toff++;
1686                 ret++;
1687         } while (--i);
1688         swap_device_unlock(swapdev);
1689         return ret;
1690 }