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