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/module.h>
  25#include <linux/ksm.h>
  26#include <linux/rmap.h>
  27#include <linux/security.h>
  28#include <linux/backing-dev.h>
  29#include <linux/mutex.h>
  30#include <linux/capability.h>
  31#include <linux/syscalls.h>
  32#include <linux/memcontrol.h>
  33#include <linux/poll.h>
  34#include <linux/oom.h>
  35
  36#include <asm/pgtable.h>
  37#include <asm/tlbflush.h>
  38#include <linux/swapops.h>
  39#include <linux/page_cgroup.h>
  40
  41static bool swap_count_continued(struct swap_info_struct *, pgoff_t,
  42                                 unsigned char);
  43static void free_swap_count_continuations(struct swap_info_struct *);
  44static sector_t map_swap_entry(swp_entry_t, struct block_device**);
  45
  46static DEFINE_SPINLOCK(swap_lock);
  47static unsigned int nr_swapfiles;
  48long nr_swap_pages;
  49long total_swap_pages;
  50static int least_priority;
  51
  52static const char Bad_file[] = "Bad swap file entry ";
  53static const char Unused_file[] = "Unused swap file entry ";
  54static const char Bad_offset[] = "Bad swap offset entry ";
  55static const char Unused_offset[] = "Unused swap offset entry ";
  56
  57static struct swap_list_t swap_list = {-1, -1};
  58
  59static struct swap_info_struct *swap_info[MAX_SWAPFILES];
  60
  61static DEFINE_MUTEX(swapon_mutex);
  62
  63static DECLARE_WAIT_QUEUE_HEAD(proc_poll_wait);
  64/* Activity counter to indicate that a swapon or swapoff has occurred */
  65static atomic_t proc_poll_event = ATOMIC_INIT(0);
  66
  67static inline unsigned char swap_count(unsigned char ent)
  68{
  69        return ent & ~SWAP_HAS_CACHE;   /* may include SWAP_HAS_CONT flag */
  70}
  71
  72/* returns 1 if swap entry is freed */
  73static int
  74__try_to_reclaim_swap(struct swap_info_struct *si, unsigned long offset)
  75{
  76        swp_entry_t entry = swp_entry(si->type, offset);
  77        struct page *page;
  78        int ret = 0;
  79
  80        page = find_get_page(&swapper_space, entry.val);
  81        if (!page)
  82                return 0;
  83        /*
  84         * This function is called from scan_swap_map() and it's called
  85         * by vmscan.c at reclaiming pages. So, we hold a lock on a page, here.
  86         * We have to use trylock for avoiding deadlock. This is a special
  87         * case and you should use try_to_free_swap() with explicit lock_page()
  88         * in usual operations.
  89         */
  90        if (trylock_page(page)) {
  91                ret = try_to_free_swap(page);
  92                unlock_page(page);
  93        }
  94        page_cache_release(page);
  95        return ret;
  96}
  97
  98/*
  99 * swapon tell device that all the old swap contents can be discarded,
 100 * to allow the swap device to optimize its wear-levelling.
 101 */
 102static int discard_swap(struct swap_info_struct *si)
 103{
 104        struct swap_extent *se;
 105        sector_t start_block;
 106        sector_t nr_blocks;
 107        int err = 0;
 108
 109        /* Do not discard the swap header page! */
 110        se = &si->first_swap_extent;
 111        start_block = (se->start_block + 1) << (PAGE_SHIFT - 9);
 112        nr_blocks = ((sector_t)se->nr_pages - 1) << (PAGE_SHIFT - 9);
 113        if (nr_blocks) {
 114                err = blkdev_issue_discard(si->bdev, start_block,
 115                                nr_blocks, GFP_KERNEL, 0);
 116                if (err)
 117                        return err;
 118                cond_resched();
 119        }
 120
 121        list_for_each_entry(se, &si->first_swap_extent.list, list) {
 122                start_block = se->start_block << (PAGE_SHIFT - 9);
 123                nr_blocks = (sector_t)se->nr_pages << (PAGE_SHIFT - 9);
 124
 125                err = blkdev_issue_discard(si->bdev, start_block,
 126                                nr_blocks, GFP_KERNEL, 0);
 127                if (err)
 128                        break;
 129
 130                cond_resched();
 131        }
 132        return err;             /* That will often be -EOPNOTSUPP */
 133}
 134
 135/*
 136 * swap allocation tell device that a cluster of swap can now be discarded,
 137 * to allow the swap device to optimize its wear-levelling.
 138 */
 139static void discard_swap_cluster(struct swap_info_struct *si,
 140                                 pgoff_t start_page, pgoff_t nr_pages)
 141{
 142        struct swap_extent *se = si->curr_swap_extent;
 143        int found_extent = 0;
 144
 145        while (nr_pages) {
 146                struct list_head *lh;
 147
 148                if (se->start_page <= start_page &&
 149                    start_page < se->start_page + se->nr_pages) {
 150                        pgoff_t offset = start_page - se->start_page;
 151                        sector_t start_block = se->start_block + offset;
 152                        sector_t nr_blocks = se->nr_pages - offset;
 153
 154                        if (nr_blocks > nr_pages)
 155                                nr_blocks = nr_pages;
 156                        start_page += nr_blocks;
 157                        nr_pages -= nr_blocks;
 158
 159                        if (!found_extent++)
 160                                si->curr_swap_extent = se;
 161
 162                        start_block <<= PAGE_SHIFT - 9;
 163                        nr_blocks <<= PAGE_SHIFT - 9;
 164                        if (blkdev_issue_discard(si->bdev, start_block,
 165                                    nr_blocks, GFP_NOIO, 0))
 166                                break;
 167                }
 168
 169                lh = se->list.next;
 170                se = list_entry(lh, struct swap_extent, list);
 171        }
 172}
 173
 174static int wait_for_discard(void *word)
 175{
 176        schedule();
 177        return 0;
 178}
 179
 180#define SWAPFILE_CLUSTER        256
 181#define LATENCY_LIMIT           256
 182
 183static unsigned long scan_swap_map(struct swap_info_struct *si,
 184                                   unsigned char usage)
 185{
 186        unsigned long offset;
 187        unsigned long scan_base;
 188        unsigned long last_in_cluster = 0;
 189        int latency_ration = LATENCY_LIMIT;
 190        int found_free_cluster = 0;
 191
 192        /*
 193         * We try to cluster swap pages by allocating them sequentially
 194         * in swap.  Once we've allocated SWAPFILE_CLUSTER pages this
 195         * way, however, we resort to first-free allocation, starting
 196         * a new cluster.  This prevents us from scattering swap pages
 197         * all over the entire swap partition, so that we reduce
 198         * overall disk seek times between swap pages.  -- sct
 199         * But we do now try to find an empty cluster.  -Andrea
 200         * And we let swap pages go all over an SSD partition.  Hugh
 201         */
 202
 203        si->flags += SWP_SCANNING;
 204        scan_base = offset = si->cluster_next;
 205
 206        if (unlikely(!si->cluster_nr--)) {
 207                if (si->pages - si->inuse_pages < SWAPFILE_CLUSTER) {
 208                        si->cluster_nr = SWAPFILE_CLUSTER - 1;
 209                        goto checks;
 210                }
 211                if (si->flags & SWP_DISCARDABLE) {
 212                        /*
 213                         * Start range check on racing allocations, in case
 214                         * they overlap the cluster we eventually decide on
 215                         * (we scan without swap_lock to allow preemption).
 216                         * It's hardly conceivable that cluster_nr could be
 217                         * wrapped during our scan, but don't depend on it.
 218                         */
 219                        if (si->lowest_alloc)
 220                                goto checks;
 221                        si->lowest_alloc = si->max;
 222                        si->highest_alloc = 0;
 223                }
 224                spin_unlock(&swap_lock);
 225
 226                /*
 227                 * If seek is expensive, start searching for new cluster from
 228                 * start of partition, to minimize the span of allocated swap.
 229                 * But if seek is cheap, search from our current position, so
 230                 * that swap is allocated from all over the partition: if the
 231                 * Flash Translation Layer only remaps within limited zones,
 232                 * we don't want to wear out the first zone too quickly.
 233                 */
 234                if (!(si->flags & SWP_SOLIDSTATE))
 235                        scan_base = offset = si->lowest_bit;
 236                last_in_cluster = offset + SWAPFILE_CLUSTER - 1;
 237
 238                /* Locate the first empty (unaligned) cluster */
 239                for (; last_in_cluster <= si->highest_bit; offset++) {
 240                        if (si->swap_map[offset])
 241                                last_in_cluster = offset + SWAPFILE_CLUSTER;
 242                        else if (offset == last_in_cluster) {
 243                                spin_lock(&swap_lock);
 244                                offset -= SWAPFILE_CLUSTER - 1;
 245                                si->cluster_next = offset;
 246                                si->cluster_nr = SWAPFILE_CLUSTER - 1;
 247                                found_free_cluster = 1;
 248                                goto checks;
 249                        }
 250                        if (unlikely(--latency_ration < 0)) {
 251                                cond_resched();
 252                                latency_ration = LATENCY_LIMIT;
 253                        }
 254                }
 255
 256                offset = si->lowest_bit;
 257                last_in_cluster = offset + SWAPFILE_CLUSTER - 1;
 258
 259                /* Locate the first empty (unaligned) cluster */
 260                for (; last_in_cluster < scan_base; offset++) {
 261                        if (si->swap_map[offset])
 262                                last_in_cluster = offset + SWAPFILE_CLUSTER;
 263                        else if (offset == last_in_cluster) {
 264                                spin_lock(&swap_lock);
 265                                offset -= SWAPFILE_CLUSTER - 1;
 266                                si->cluster_next = offset;
 267                                si->cluster_nr = SWAPFILE_CLUSTER - 1;
 268                                found_free_cluster = 1;
 269                                goto checks;
 270                        }
 271                        if (unlikely(--latency_ration < 0)) {
 272                                cond_resched();
 273                                latency_ration = LATENCY_LIMIT;
 274                        }
 275                }
 276
 277                offset = scan_base;
 278                spin_lock(&swap_lock);
 279                si->cluster_nr = SWAPFILE_CLUSTER - 1;
 280                si->lowest_alloc = 0;
 281        }
 282
 283checks:
 284        if (!(si->flags & SWP_WRITEOK))
 285                goto no_page;
 286        if (!si->highest_bit)
 287                goto no_page;
 288        if (offset > si->highest_bit)
 289                scan_base = offset = si->lowest_bit;
 290
 291        /* reuse swap entry of cache-only swap if not busy. */
 292        if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {
 293                int swap_was_freed;
 294                spin_unlock(&swap_lock);
 295                swap_was_freed = __try_to_reclaim_swap(si, offset);
 296                spin_lock(&swap_lock);
 297                /* entry was freed successfully, try to use this again */
 298                if (swap_was_freed)
 299                        goto checks;
 300                goto scan; /* check next one */
 301        }
 302
 303        if (si->swap_map[offset])
 304                goto scan;
 305
 306        if (offset == si->lowest_bit)
 307                si->lowest_bit++;
 308        if (offset == si->highest_bit)
 309                si->highest_bit--;
 310        si->inuse_pages++;
 311        if (si->inuse_pages == si->pages) {
 312                si->lowest_bit = si->max;
 313                si->highest_bit = 0;
 314        }
 315        si->swap_map[offset] = usage;
 316        si->cluster_next = offset + 1;
 317        si->flags -= SWP_SCANNING;
 318
 319        if (si->lowest_alloc) {
 320                /*
 321                 * Only set when SWP_DISCARDABLE, and there's a scan
 322                 * for a free cluster in progress or just completed.
 323                 */
 324                if (found_free_cluster) {
 325                        /*
 326                         * To optimize wear-levelling, discard the
 327                         * old data of the cluster, taking care not to
 328                         * discard any of its pages that have already
 329                         * been allocated by racing tasks (offset has
 330                         * already stepped over any at the beginning).
 331                         */
 332                        if (offset < si->highest_alloc &&
 333                            si->lowest_alloc <= last_in_cluster)
 334                                last_in_cluster = si->lowest_alloc - 1;
 335                        si->flags |= SWP_DISCARDING;
 336                        spin_unlock(&swap_lock);
 337
 338                        if (offset < last_in_cluster)
 339                                discard_swap_cluster(si, offset,
 340                                        last_in_cluster - offset + 1);
 341
 342                        spin_lock(&swap_lock);
 343                        si->lowest_alloc = 0;
 344                        si->flags &= ~SWP_DISCARDING;
 345
 346                        smp_mb();       /* wake_up_bit advises this */
 347                        wake_up_bit(&si->flags, ilog2(SWP_DISCARDING));
 348
 349                } else if (si->flags & SWP_DISCARDING) {
 350                        /*
 351                         * Delay using pages allocated by racing tasks
 352                         * until the whole discard has been issued. We
 353                         * could defer that delay until swap_writepage,
 354                         * but it's easier to keep this self-contained.
 355                         */
 356                        spin_unlock(&swap_lock);
 357                        wait_on_bit(&si->flags, ilog2(SWP_DISCARDING),
 358                                wait_for_discard, TASK_UNINTERRUPTIBLE);
 359                        spin_lock(&swap_lock);
 360                } else {
 361                        /*
 362                         * Note pages allocated by racing tasks while
 363                         * scan for a free cluster is in progress, so
 364                         * that its final discard can exclude them.
 365                         */
 366                        if (offset < si->lowest_alloc)
 367                                si->lowest_alloc = offset;
 368                        if (offset > si->highest_alloc)
 369                                si->highest_alloc = offset;
 370                }
 371        }
 372        return offset;
 373
 374scan:
 375        spin_unlock(&swap_lock);
 376        while (++offset <= si->highest_bit) {
 377                if (!si->swap_map[offset]) {
 378                        spin_lock(&swap_lock);
 379                        goto checks;
 380                }
 381                if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {
 382                        spin_lock(&swap_lock);
 383                        goto checks;
 384                }
 385                if (unlikely(--latency_ration < 0)) {
 386                        cond_resched();
 387                        latency_ration = LATENCY_LIMIT;
 388                }
 389        }
 390        offset = si->lowest_bit;
 391        while (++offset < scan_base) {
 392                if (!si->swap_map[offset]) {
 393                        spin_lock(&swap_lock);
 394                        goto checks;
 395                }
 396                if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {
 397                        spin_lock(&swap_lock);
 398                        goto checks;
 399                }
 400                if (unlikely(--latency_ration < 0)) {
 401                        cond_resched();
 402                        latency_ration = LATENCY_LIMIT;
 403                }
 404        }
 405        spin_lock(&swap_lock);
 406
 407no_page:
 408        si->flags -= SWP_SCANNING;
 409        return 0;
 410}
 411
 412swp_entry_t get_swap_page(void)
 413{
 414        struct swap_info_struct *si;
 415        pgoff_t offset;
 416        int type, next;
 417        int wrapped = 0;
 418
 419        spin_lock(&swap_lock);
 420        if (nr_swap_pages <= 0)
 421                goto noswap;
 422        nr_swap_pages--;
 423
 424        for (type = swap_list.next; type >= 0 && wrapped < 2; type = next) {
 425                si = swap_info[type];
 426                next = si->next;
 427                if (next < 0 ||
 428                    (!wrapped && si->prio != swap_info[next]->prio)) {
 429                        next = swap_list.head;
 430                        wrapped++;
 431                }
 432
 433                if (!si->highest_bit)
 434                        continue;
 435                if (!(si->flags & SWP_WRITEOK))
 436                        continue;
 437
 438                swap_list.next = next;
 439                /* This is called for allocating swap entry for cache */
 440                offset = scan_swap_map(si, SWAP_HAS_CACHE);
 441                if (offset) {
 442                        spin_unlock(&swap_lock);
 443                        return swp_entry(type, offset);
 444                }
 445                next = swap_list.next;
 446        }
 447
 448        nr_swap_pages++;
 449noswap:
 450        spin_unlock(&swap_lock);
 451        return (swp_entry_t) {0};
 452}
 453
 454/* The only caller of this function is now susupend routine */
 455swp_entry_t get_swap_page_of_type(int type)
 456{
 457        struct swap_info_struct *si;
 458        pgoff_t offset;
 459
 460        spin_lock(&swap_lock);
 461        si = swap_info[type];
 462        if (si && (si->flags & SWP_WRITEOK)) {
 463                nr_swap_pages--;
 464                /* This is called for allocating swap entry, not cache */
 465                offset = scan_swap_map(si, 1);
 466                if (offset) {
 467                        spin_unlock(&swap_lock);
 468                        return swp_entry(type, offset);
 469                }
 470                nr_swap_pages++;
 471        }
 472        spin_unlock(&swap_lock);
 473        return (swp_entry_t) {0};
 474}
 475
 476static struct swap_info_struct *swap_info_get(swp_entry_t entry)
 477{
 478        struct swap_info_struct *p;
 479        unsigned long offset, type;
 480
 481        if (!entry.val)
 482                goto out;
 483        type = swp_type(entry);
 484        if (type >= nr_swapfiles)
 485                goto bad_nofile;
 486        p = swap_info[type];
 487        if (!(p->flags & SWP_USED))
 488                goto bad_device;
 489        offset = swp_offset(entry);
 490        if (offset >= p->max)
 491                goto bad_offset;
 492        if (!p->swap_map[offset])
 493                goto bad_free;
 494        spin_lock(&swap_lock);
 495        return p;
 496
 497bad_free:
 498        printk(KERN_ERR "swap_free: %s%08lx\n", Unused_offset, entry.val);
 499        goto out;
 500bad_offset:
 501        printk(KERN_ERR "swap_free: %s%08lx\n", Bad_offset, entry.val);
 502        goto out;
 503bad_device:
 504        printk(KERN_ERR "swap_free: %s%08lx\n", Unused_file, entry.val);
 505        goto out;
 506bad_nofile:
 507        printk(KERN_ERR "swap_free: %s%08lx\n", Bad_file, entry.val);
 508out:
 509        return NULL;
 510}
 511
 512static unsigned char swap_entry_free(struct swap_info_struct *p,
 513                                     swp_entry_t entry, unsigned char usage)
 514{
 515        unsigned long offset = swp_offset(entry);
 516        unsigned char count;
 517        unsigned char has_cache;
 518
 519        count = p->swap_map[offset];
 520        has_cache = count & SWAP_HAS_CACHE;
 521        count &= ~SWAP_HAS_CACHE;
 522
 523        if (usage == SWAP_HAS_CACHE) {
 524                VM_BUG_ON(!has_cache);
 525                has_cache = 0;
 526        } else if (count == SWAP_MAP_SHMEM) {
 527                /*
 528                 * Or we could insist on shmem.c using a special
 529                 * swap_shmem_free() and free_shmem_swap_and_cache()...
 530                 */
 531                count = 0;
 532        } else if ((count & ~COUNT_CONTINUED) <= SWAP_MAP_MAX) {
 533                if (count == COUNT_CONTINUED) {
 534                        if (swap_count_continued(p, offset, count))
 535                                count = SWAP_MAP_MAX | COUNT_CONTINUED;
 536                        else
 537                                count = SWAP_MAP_MAX;
 538                } else
 539                        count--;
 540        }
 541
 542        if (!count)
 543                mem_cgroup_uncharge_swap(entry);
 544
 545        usage = count | has_cache;
 546        p->swap_map[offset] = usage;
 547
 548        /* free if no reference */
 549        if (!usage) {
 550                struct gendisk *disk = p->bdev->bd_disk;
 551                if (offset < p->lowest_bit)
 552                        p->lowest_bit = offset;
 553                if (offset > p->highest_bit)
 554                        p->highest_bit = offset;
 555                if (swap_list.next >= 0 &&
 556                    p->prio > swap_info[swap_list.next]->prio)
 557                        swap_list.next = p->type;
 558                nr_swap_pages++;
 559                p->inuse_pages--;
 560                if ((p->flags & SWP_BLKDEV) &&
 561                                disk->fops->swap_slot_free_notify)
 562                        disk->fops->swap_slot_free_notify(p->bdev, offset);
 563        }
 564
 565        return usage;
 566}
 567
 568/*
 569 * Caller has made sure that the swapdevice corresponding to entry
 570 * is still around or has not been recycled.
 571 */
 572void swap_free(swp_entry_t entry)
 573{
 574        struct swap_info_struct *p;
 575
 576        p = swap_info_get(entry);
 577        if (p) {
 578                swap_entry_free(p, entry, 1);
 579                spin_unlock(&swap_lock);
 580        }
 581}
 582
 583/*
 584 * Called after dropping swapcache to decrease refcnt to swap entries.
 585 */
 586void swapcache_free(swp_entry_t entry, struct page *page)
 587{
 588        struct swap_info_struct *p;
 589        unsigned char count;
 590
 591        p = swap_info_get(entry);
 592        if (p) {
 593                count = swap_entry_free(p, entry, SWAP_HAS_CACHE);
 594                if (page)
 595                        mem_cgroup_uncharge_swapcache(page, entry, count != 0);
 596                spin_unlock(&swap_lock);
 597        }
 598}
 599
 600/*
 601 * How many references to page are currently swapped out?
 602 * This does not give an exact answer when swap count is continued,
 603 * but does include the high COUNT_CONTINUED flag to allow for that.
 604 */
 605static inline int page_swapcount(struct page *page)
 606{
 607        int count = 0;
 608        struct swap_info_struct *p;
 609        swp_entry_t entry;
 610
 611        entry.val = page_private(page);
 612        p = swap_info_get(entry);
 613        if (p) {
 614                count = swap_count(p->swap_map[swp_offset(entry)]);
 615                spin_unlock(&swap_lock);
 616        }
 617        return count;
 618}
 619
 620/*
 621 * We can write to an anon page without COW if there are no other references
 622 * to it.  And as a side-effect, free up its swap: because the old content
 623 * on disk will never be read, and seeking back there to write new content
 624 * later would only waste time away from clustering.
 625 */
 626int reuse_swap_page(struct page *page)
 627{
 628        int count;
 629
 630        VM_BUG_ON(!PageLocked(page));
 631        if (unlikely(PageKsm(page)))
 632                return 0;
 633        count = page_mapcount(page);
 634        if (count <= 1 && PageSwapCache(page)) {
 635                count += page_swapcount(page);
 636                if (count == 1 && !PageWriteback(page)) {
 637                        delete_from_swap_cache(page);
 638                        SetPageDirty(page);
 639                }
 640        }
 641        return count <= 1;
 642}
 643
 644/*
 645 * If swap is getting full, or if there are no more mappings of this page,
 646 * then try_to_free_swap is called to free its swap space.
 647 */
 648int try_to_free_swap(struct page *page)
 649{
 650        VM_BUG_ON(!PageLocked(page));
 651
 652        if (!PageSwapCache(page))
 653                return 0;
 654        if (PageWriteback(page))
 655                return 0;
 656        if (page_swapcount(page))
 657                return 0;
 658
 659        /*
 660         * Once hibernation has begun to create its image of memory,
 661         * there's a danger that one of the calls to try_to_free_swap()
 662         * - most probably a call from __try_to_reclaim_swap() while
 663         * hibernation is allocating its own swap pages for the image,
 664         * but conceivably even a call from memory reclaim - will free
 665         * the swap from a page which has already been recorded in the
 666         * image as a clean swapcache page, and then reuse its swap for
 667         * another page of the image.  On waking from hibernation, the
 668         * original page might be freed under memory pressure, then
 669         * later read back in from swap, now with the wrong data.
 670         *
 671         * Hibernation clears bits from gfp_allowed_mask to prevent
 672         * memory reclaim from writing to disk, so check that here.
 673         */
 674        if (!(gfp_allowed_mask & __GFP_IO))
 675                return 0;
 676
 677        delete_from_swap_cache(page);
 678        SetPageDirty(page);
 679        return 1;
 680}
 681
 682/*
 683 * Free the swap entry like above, but also try to
 684 * free the page cache entry if it is the last user.
 685 */
 686int free_swap_and_cache(swp_entry_t entry)
 687{
 688        struct swap_info_struct *p;
 689        struct page *page = NULL;
 690
 691        if (non_swap_entry(entry))
 692                return 1;
 693
 694        p = swap_info_get(entry);
 695        if (p) {
 696                if (swap_entry_free(p, entry, 1) == SWAP_HAS_CACHE) {
 697                        page = find_get_page(&swapper_space, entry.val);
 698                        if (page && !trylock_page(page)) {
 699                                page_cache_release(page);
 700                                page = NULL;
 701                        }
 702                }
 703                spin_unlock(&swap_lock);
 704        }
 705        if (page) {
 706                /*
 707                 * Not mapped elsewhere, or swap space full? Free it!
 708                 * Also recheck PageSwapCache now page is locked (above).
 709                 */
 710                if (PageSwapCache(page) && !PageWriteback(page) &&
 711                                (!page_mapped(page) || vm_swap_full())) {
 712                        delete_from_swap_cache(page);
 713                        SetPageDirty(page);
 714                }
 715                unlock_page(page);
 716                page_cache_release(page);
 717        }
 718        return p != NULL;
 719}
 720
 721#ifdef CONFIG_CGROUP_MEM_RES_CTLR
 722/**
 723 * mem_cgroup_count_swap_user - count the user of a swap entry
 724 * @ent: the swap entry to be checked
 725 * @pagep: the pointer for the swap cache page of the entry to be stored
 726 *
 727 * Returns the number of the user of the swap entry. The number is valid only
 728 * for swaps of anonymous pages.
 729 * If the entry is found on swap cache, the page is stored to pagep with
 730 * refcount of it being incremented.
 731 */
 732int mem_cgroup_count_swap_user(swp_entry_t ent, struct page **pagep)
 733{
 734        struct page *page;
 735        struct swap_info_struct *p;
 736        int count = 0;
 737
 738        page = find_get_page(&swapper_space, ent.val);
 739        if (page)
 740                count += page_mapcount(page);
 741        p = swap_info_get(ent);
 742        if (p) {
 743                count += swap_count(p->swap_map[swp_offset(ent)]);
 744                spin_unlock(&swap_lock);
 745        }
 746
 747        *pagep = page;
 748        return count;
 749}
 750#endif
 751
 752#ifdef CONFIG_HIBERNATION
 753/*
 754 * Find the swap type that corresponds to given device (if any).
 755 *
 756 * @offset - number of the PAGE_SIZE-sized block of the device, starting
 757 * from 0, in which the swap header is expected to be located.
 758 *
 759 * This is needed for the suspend to disk (aka swsusp).
 760 */
 761int swap_type_of(dev_t device, sector_t offset, struct block_device **bdev_p)
 762{
 763        struct block_device *bdev = NULL;
 764        int type;
 765
 766        if (device)
 767                bdev = bdget(device);
 768
 769        spin_lock(&swap_lock);
 770        for (type = 0; type < nr_swapfiles; type++) {
 771                struct swap_info_struct *sis = swap_info[type];
 772
 773                if (!(sis->flags & SWP_WRITEOK))
 774                        continue;
 775
 776                if (!bdev) {
 777                        if (bdev_p)
 778                                *bdev_p = bdgrab(sis->bdev);
 779
 780                        spin_unlock(&swap_lock);
 781                        return type;
 782                }
 783                if (bdev == sis->bdev) {
 784                        struct swap_extent *se = &sis->first_swap_extent;
 785
 786                        if (se->start_block == offset) {
 787                                if (bdev_p)
 788                                        *bdev_p = bdgrab(sis->bdev);
 789
 790                                spin_unlock(&swap_lock);
 791                                bdput(bdev);
 792                                return type;
 793                        }
 794                }
 795        }
 796        spin_unlock(&swap_lock);
 797        if (bdev)
 798                bdput(bdev);
 799
 800        return -ENODEV;
 801}
 802
 803/*
 804 * Get the (PAGE_SIZE) block corresponding to given offset on the swapdev
 805 * corresponding to given index in swap_info (swap type).
 806 */
 807sector_t swapdev_block(int type, pgoff_t offset)
 808{
 809        struct block_device *bdev;
 810
 811        if ((unsigned int)type >= nr_swapfiles)
 812                return 0;
 813        if (!(swap_info[type]->flags & SWP_WRITEOK))
 814                return 0;
 815        return map_swap_entry(swp_entry(type, offset), &bdev);
 816}
 817
 818/*
 819 * Return either the total number of swap pages of given type, or the number
 820 * of free pages of that type (depending on @free)
 821 *
 822 * This is needed for software suspend
 823 */
 824unsigned int count_swap_pages(int type, int free)
 825{
 826        unsigned int n = 0;
 827
 828        spin_lock(&swap_lock);
 829        if ((unsigned int)type < nr_swapfiles) {
 830                struct swap_info_struct *sis = swap_info[type];
 831
 832                if (sis->flags & SWP_WRITEOK) {
 833                        n = sis->pages;
 834                        if (free)
 835                                n -= sis->inuse_pages;
 836                }
 837        }
 838        spin_unlock(&swap_lock);
 839        return n;
 840}
 841#endif /* CONFIG_HIBERNATION */
 842
 843/*
 844 * No need to decide whether this PTE shares the swap entry with others,
 845 * just let do_wp_page work it out if a write is requested later - to
 846 * force COW, vm_page_prot omits write permission from any private vma.
 847 */
 848static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
 849                unsigned long addr, swp_entry_t entry, struct page *page)
 850{
 851        struct mem_cgroup *ptr;
 852        spinlock_t *ptl;
 853        pte_t *pte;
 854        int ret = 1;
 855
 856        if (mem_cgroup_try_charge_swapin(vma->vm_mm, page, GFP_KERNEL, &ptr)) {
 857                ret = -ENOMEM;
 858                goto out_nolock;
 859        }
 860
 861        pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
 862        if (unlikely(!pte_same(*pte, swp_entry_to_pte(entry)))) {
 863                if (ret > 0)
 864                        mem_cgroup_cancel_charge_swapin(ptr);
 865                ret = 0;
 866                goto out;
 867        }
 868
 869        dec_mm_counter(vma->vm_mm, MM_SWAPENTS);
 870        inc_mm_counter(vma->vm_mm, MM_ANONPAGES);
 871        get_page(page);
 872        set_pte_at(vma->vm_mm, addr, pte,
 873                   pte_mkold(mk_pte(page, vma->vm_page_prot)));
 874        page_add_anon_rmap(page, vma, addr);
 875        mem_cgroup_commit_charge_swapin(page, ptr);
 876        swap_free(entry);
 877        /*
 878         * Move the page to the active list so it is not
 879         * immediately swapped out again after swapon.
 880         */
 881        activate_page(page);
 882out:
 883        pte_unmap_unlock(pte, ptl);
 884out_nolock:
 885        return ret;
 886}
 887
 888static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
 889                                unsigned long addr, unsigned long end,
 890                                swp_entry_t entry, struct page *page)
 891{
 892        pte_t swp_pte = swp_entry_to_pte(entry);
 893        pte_t *pte;
 894        int ret = 0;
 895
 896        /*
 897         * We don't actually need pte lock while scanning for swp_pte: since
 898         * we hold page lock and mmap_sem, swp_pte cannot be inserted into the
 899         * page table while we're scanning; though it could get zapped, and on
 900         * some architectures (e.g. x86_32 with PAE) we might catch a glimpse
 901         * of unmatched parts which look like swp_pte, so unuse_pte must
 902         * recheck under pte lock.  Scanning without pte lock lets it be
 903         * preemptible whenever CONFIG_PREEMPT but not CONFIG_HIGHPTE.
 904         */
 905        pte = pte_offset_map(pmd, addr);
 906        do {
 907                /*
 908                 * swapoff spends a _lot_ of time in this loop!
 909                 * Test inline before going to call unuse_pte.
 910                 */
 911                if (unlikely(pte_same(*pte, swp_pte))) {
 912                        pte_unmap(pte);
 913                        ret = unuse_pte(vma, pmd, addr, entry, page);
 914                        if (ret)
 915                                goto out;
 916                        pte = pte_offset_map(pmd, addr);
 917                }
 918        } while (pte++, addr += PAGE_SIZE, addr != end);
 919        pte_unmap(pte - 1);
 920out:
 921        return ret;
 922}
 923
 924static inline int unuse_pmd_range(struct vm_area_struct *vma, pud_t *pud,
 925                                unsigned long addr, unsigned long end,
 926                                swp_entry_t entry, struct page *page)
 927{
 928        pmd_t *pmd;
 929        unsigned long next;
 930        int ret;
 931
 932        pmd = pmd_offset(pud, addr);
 933        do {
 934                next = pmd_addr_end(addr, end);
 935                if (unlikely(pmd_trans_huge(*pmd)))
 936                        continue;
 937                if (pmd_none_or_clear_bad(pmd))
 938                        continue;
 939                ret = unuse_pte_range(vma, pmd, addr, next, entry, page);
 940                if (ret)
 941                        return ret;
 942        } while (pmd++, addr = next, addr != end);
 943        return 0;
 944}
 945
 946static inline int unuse_pud_range(struct vm_area_struct *vma, pgd_t *pgd,
 947                                unsigned long addr, unsigned long end,
 948                                swp_entry_t entry, struct page *page)
 949{
 950        pud_t *pud;
 951        unsigned long next;
 952        int ret;
 953
 954        pud = pud_offset(pgd, addr);
 955        do {
 956                next = pud_addr_end(addr, end);
 957                if (pud_none_or_clear_bad(pud))
 958                        continue;
 959                ret = unuse_pmd_range(vma, pud, addr, next, entry, page);
 960                if (ret)
 961                        return ret;
 962        } while (pud++, addr = next, addr != end);
 963        return 0;
 964}
 965
 966static int unuse_vma(struct vm_area_struct *vma,
 967                                swp_entry_t entry, struct page *page)
 968{
 969        pgd_t *pgd;
 970        unsigned long addr, end, next;
 971        int ret;
 972
 973        if (page_anon_vma(page)) {
 974                addr = page_address_in_vma(page, vma);
 975                if (addr == -EFAULT)
 976                        return 0;
 977                else
 978                        end = addr + PAGE_SIZE;
 979        } else {
 980                addr = vma->vm_start;
 981                end = vma->vm_end;
 982        }
 983
 984        pgd = pgd_offset(vma->vm_mm, addr);
 985        do {
 986                next = pgd_addr_end(addr, end);
 987                if (pgd_none_or_clear_bad(pgd))
 988                        continue;
 989                ret = unuse_pud_range(vma, pgd, addr, next, entry, page);
 990                if (ret)
 991                        return ret;
 992        } while (pgd++, addr = next, addr != end);
 993        return 0;
 994}
 995
 996static int unuse_mm(struct mm_struct *mm,
 997                                swp_entry_t entry, struct page *page)
 998{
 999        struct vm_area_struct *vma;
1000        int ret = 0;
1001
1002        if (!down_read_trylock(&mm->mmap_sem)) {
1003                /*
1004                 * Activate page so shrink_inactive_list is unlikely to unmap
1005                 * its ptes while lock is dropped, so swapoff can make progress.
1006                 */
1007                activate_page(page);
1008                unlock_page(page);
1009                down_read(&mm->mmap_sem);
1010                lock_page(page);
1011        }
1012        for (vma = mm->mmap; vma; vma = vma->vm_next) {
1013                if (vma->anon_vma && (ret = unuse_vma(vma, entry, page)))
1014                        break;
1015        }
1016        up_read(&mm->mmap_sem);
1017        return (ret < 0)? ret: 0;
1018}
1019
1020/*
1021 * Scan swap_map from current position to next entry still in use.
1022 * Recycle to start on reaching the end, returning 0 when empty.
1023 */
1024static unsigned int find_next_to_unuse(struct swap_info_struct *si,
1025                                        unsigned int prev)
1026{
1027        unsigned int max = si->max;
1028        unsigned int i = prev;
1029        unsigned char count;
1030
1031        /*
1032         * No need for swap_lock here: we're just looking
1033         * for whether an entry is in use, not modifying it; false
1034         * hits are okay, and sys_swapoff() has already prevented new
1035         * allocations from this area (while holding swap_lock).
1036         */
1037        for (;;) {
1038                if (++i >= max) {
1039                        if (!prev) {
1040                                i = 0;
1041                                break;
1042                        }
1043                        /*
1044                         * No entries in use at top of swap_map,
1045                         * loop back to start and recheck there.
1046                         */
1047                        max = prev + 1;
1048                        prev = 0;
1049                        i = 1;
1050                }
1051                count = si->swap_map[i];
1052                if (count && swap_count(count) != SWAP_MAP_BAD)
1053                        break;
1054        }
1055        return i;
1056}
1057
1058/*
1059 * We completely avoid races by reading each swap page in advance,
1060 * and then search for the process using it.  All the necessary
1061 * page table adjustments can then be made atomically.
1062 */
1063static int try_to_unuse(unsigned int type)
1064{
1065        struct swap_info_struct *si = swap_info[type];
1066        struct mm_struct *start_mm;
1067        unsigned char *swap_map;
1068        unsigned char swcount;
1069        struct page *page;
1070        swp_entry_t entry;
1071        unsigned int i = 0;
1072        int retval = 0;
1073
1074        /*
1075         * When searching mms for an entry, a good strategy is to
1076         * start at the first mm we freed the previous entry from
1077         * (though actually we don't notice whether we or coincidence
1078         * freed the entry).  Initialize this start_mm with a hold.
1079         *
1080         * A simpler strategy would be to start at the last mm we
1081         * freed the previous entry from; but that would take less
1082         * advantage of mmlist ordering, which clusters forked mms
1083         * together, child after parent.  If we race with dup_mmap(), we
1084         * prefer to resolve parent before child, lest we miss entries
1085         * duplicated after we scanned child: using last mm would invert
1086         * that.
1087         */
1088        start_mm = &init_mm;
1089        atomic_inc(&init_mm.mm_users);
1090
1091        /*
1092         * Keep on scanning until all entries have gone.  Usually,
1093         * one pass through swap_map is enough, but not necessarily:
1094         * there are races when an instance of an entry might be missed.
1095         */
1096        while ((i = find_next_to_unuse(si, i)) != 0) {
1097                if (signal_pending(current)) {
1098                        retval = -EINTR;
1099                        break;
1100                }
1101
1102                /*
1103                 * Get a page for the entry, using the existing swap
1104                 * cache page if there is one.  Otherwise, get a clean
1105                 * page and read the swap into it.
1106                 */
1107                swap_map = &si->swap_map[i];
1108                entry = swp_entry(type, i);
1109                page = read_swap_cache_async(entry,
1110                                        GFP_HIGHUSER_MOVABLE, NULL, 0);
1111                if (!page) {
1112                        /*
1113                         * Either swap_duplicate() failed because entry
1114                         * has been freed independently, and will not be
1115                         * reused since sys_swapoff() already disabled
1116                         * allocation from here, or alloc_page() failed.
1117                         */
1118                        if (!*swap_map)
1119                                continue;
1120                        retval = -ENOMEM;
1121                        break;
1122                }
1123
1124                /*
1125                 * Don't hold on to start_mm if it looks like exiting.
1126                 */
1127                if (atomic_read(&start_mm->mm_users) == 1) {
1128                        mmput(start_mm);
1129                        start_mm = &init_mm;
1130                        atomic_inc(&init_mm.mm_users);
1131                }
1132
1133                /*
1134                 * Wait for and lock page.  When do_swap_page races with
1135                 * try_to_unuse, do_swap_page can handle the fault much
1136                 * faster than try_to_unuse can locate the entry.  This
1137                 * apparently redundant "wait_on_page_locked" lets try_to_unuse
1138                 * defer to do_swap_page in such a case - in some tests,
1139                 * do_swap_page and try_to_unuse repeatedly compete.
1140                 */
1141                wait_on_page_locked(page);
1142                wait_on_page_writeback(page);
1143                lock_page(page);
1144                wait_on_page_writeback(page);
1145
1146                /*
1147                 * Remove all references to entry.
1148                 */
1149                swcount = *swap_map;
1150                if (swap_count(swcount) == SWAP_MAP_SHMEM) {
1151                        retval = shmem_unuse(entry, page);
1152                        /* page has already been unlocked and released */
1153                        if (retval < 0)
1154                                break;
1155                        continue;
1156                }
1157                if (swap_count(swcount) && start_mm != &init_mm)
1158                        retval = unuse_mm(start_mm, entry, page);
1159
1160                if (swap_count(*swap_map)) {
1161                        int set_start_mm = (*swap_map >= swcount);
1162                        struct list_head *p = &start_mm->mmlist;
1163                        struct mm_struct *new_start_mm = start_mm;
1164                        struct mm_struct *prev_mm = start_mm;
1165                        struct mm_struct *mm;
1166
1167                        atomic_inc(&new_start_mm->mm_users);
1168                        atomic_inc(&prev_mm->mm_users);
1169                        spin_lock(&mmlist_lock);
1170                        while (swap_count(*swap_map) && !retval &&
1171                                        (p = p->next) != &start_mm->mmlist) {
1172                                mm = list_entry(p, struct mm_struct, mmlist);
1173                                if (!atomic_inc_not_zero(&mm->mm_users))
1174                                        continue;
1175                                spin_unlock(&mmlist_lock);
1176                                mmput(prev_mm);
1177                                prev_mm = mm;
1178
1179                                cond_resched();
1180
1181                                swcount = *swap_map;
1182                                if (!swap_count(swcount)) /* any usage ? */
1183                                        ;
1184                                else if (mm == &init_mm)
1185                                        set_start_mm = 1;
1186                                else
1187                                        retval = unuse_mm(mm, entry, page);
1188
1189                                if (set_start_mm && *swap_map < swcount) {
1190                                        mmput(new_start_mm);
1191                                        atomic_inc(&mm->mm_users);
1192                                        new_start_mm = mm;
1193                                        set_start_mm = 0;
1194                                }
1195                                spin_lock(&mmlist_lock);
1196                        }
1197                        spin_unlock(&mmlist_lock);
1198                        mmput(prev_mm);
1199                        mmput(start_mm);
1200                        start_mm = new_start_mm;
1201                }
1202                if (retval) {
1203                        unlock_page(page);
1204                        page_cache_release(page);
1205                        break;
1206                }
1207
1208                /*
1209                 * If a reference remains (rare), we would like to leave
1210                 * the page in the swap cache; but try_to_unmap could
1211                 * then re-duplicate the entry once we drop page lock,
1212                 * so we might loop indefinitely; also, that page could
1213                 * not be swapped out to other storage meanwhile.  So:
1214                 * delete from cache even if there's another reference,
1215                 * after ensuring that the data has been saved to disk -
1216                 * since if the reference remains (rarer), it will be
1217                 * read from disk into another page.  Splitting into two
1218                 * pages would be incorrect if swap supported "shared
1219                 * private" pages, but they are handled by tmpfs files.
1220                 *
1221                 * Given how unuse_vma() targets one particular offset
1222                 * in an anon_vma, once the anon_vma has been determined,
1223                 * this splitting happens to be just what is needed to
1224                 * handle where KSM pages have been swapped out: re-reading
1225                 * is unnecessarily slow, but we can fix that later on.
1226                 */
1227                if (swap_count(*swap_map) &&
1228                     PageDirty(page) && PageSwapCache(page)) {
1229                        struct writeback_control wbc = {
1230                                .sync_mode = WB_SYNC_NONE,
1231                        };
1232
1233                        swap_writepage(page, &wbc);
1234                        lock_page(page);
1235                        wait_on_page_writeback(page);
1236                }
1237
1238                /*
1239                 * It is conceivable that a racing task removed this page from
1240                 * swap cache just before we acquired the page lock at the top,
1241                 * or while we dropped it in unuse_mm().  The page might even
1242                 * be back in swap cache on another swap area: that we must not
1243                 * delete, since it may not have been written out to swap yet.
1244                 */
1245                if (PageSwapCache(page) &&
1246                    likely(page_private(page) == entry.val))
1247                        delete_from_swap_cache(page);
1248
1249                /*
1250                 * So we could skip searching mms once swap count went
1251                 * to 1, we did not mark any present ptes as dirty: must
1252                 * mark page dirty so shrink_page_list will preserve it.
1253                 */
1254                SetPageDirty(page);
1255                unlock_page(page);
1256                page_cache_release(page);
1257
1258                /*
1259                 * Make sure that we aren't completely killing
1260                 * interactive performance.
1261                 */
1262                cond_resched();
1263        }
1264
1265        mmput(start_mm);
1266        return retval;
1267}
1268
1269/*
1270 * After a successful try_to_unuse, if no swap is now in use, we know
1271 * we can empty the mmlist.  swap_lock must be held on entry and exit.
1272 * Note that mmlist_lock nests inside swap_lock, and an mm must be
1273 * added to the mmlist just after page_duplicate - before would be racy.
1274 */
1275static void drain_mmlist(void)
1276{
1277        struct list_head *p, *next;
1278        unsigned int type;
1279
1280        for (type = 0; type < nr_swapfiles; type++)
1281                if (swap_info[type]->inuse_pages)
1282                        return;
1283        spin_lock(&mmlist_lock);
1284        list_for_each_safe(p, next, &init_mm.mmlist)
1285                list_del_init(p);
1286        spin_unlock(&mmlist_lock);
1287}
1288
1289/*
1290 * Use this swapdev's extent info to locate the (PAGE_SIZE) block which
1291 * corresponds to page offset for the specified swap entry.
1292 * Note that the type of this function is sector_t, but it returns page offset
1293 * into the bdev, not sector offset.
1294 */
1295static sector_t map_swap_entry(swp_entry_t entry, struct block_device **bdev)
1296{
1297        struct swap_info_struct *sis;
1298        struct swap_extent *start_se;
1299        struct swap_extent *se;
1300        pgoff_t offset;
1301
1302        sis = swap_info[swp_type(entry)];
1303        *bdev = sis->bdev;
1304
1305        offset = swp_offset(entry);
1306        start_se = sis->curr_swap_extent;
1307        se = start_se;
1308
1309        for ( ; ; ) {
1310                struct list_head *lh;
1311
1312                if (se->start_page <= offset &&
1313                                offset < (se->start_page + se->nr_pages)) {
1314                        return se->start_block + (offset - se->start_page);
1315                }
1316                lh = se->list.next;
1317                se = list_entry(lh, struct swap_extent, list);
1318                sis->curr_swap_extent = se;
1319                BUG_ON(se == start_se);         /* It *must* be present */
1320        }
1321}
1322
1323/*
1324 * Returns the page offset into bdev for the specified page's swap entry.
1325 */
1326sector_t map_swap_page(struct page *page, struct block_device **bdev)
1327{
1328        swp_entry_t entry;
1329        entry.val = page_private(page);
1330        return map_swap_entry(entry, bdev);
1331}
1332
1333/*
1334 * Free all of a swapdev's extent information
1335 */
1336static void destroy_swap_extents(struct swap_info_struct *sis)
1337{
1338        while (!list_empty(&sis->first_swap_extent.list)) {
1339                struct swap_extent *se;
1340
1341                se = list_entry(sis->first_swap_extent.list.next,
1342                                struct swap_extent, list);
1343                list_del(&se->list);
1344                kfree(se);
1345        }
1346}
1347
1348/*
1349 * Add a block range (and the corresponding page range) into this swapdev's
1350 * extent list.  The extent list is kept sorted in page order.
1351 *
1352 * This function rather assumes that it is called in ascending page order.
1353 */
1354static int
1355add_swap_extent(struct swap_info_struct *sis, unsigned long start_page,
1356                unsigned long nr_pages, sector_t start_block)
1357{
1358        struct swap_extent *se;
1359        struct swap_extent *new_se;
1360        struct list_head *lh;
1361
1362        if (start_page == 0) {
1363                se = &sis->first_swap_extent;
1364                sis->curr_swap_extent = se;
1365                se->start_page = 0;
1366                se->nr_pages = nr_pages;
1367                se->start_block = start_block;
1368                return 1;
1369        } else {
1370                lh = sis->first_swap_extent.list.prev;  /* Highest extent */
1371                se = list_entry(lh, struct swap_extent, list);
1372                BUG_ON(se->start_page + se->nr_pages != start_page);
1373                if (se->start_block + se->nr_pages == start_block) {
1374                        /* Merge it */
1375                        se->nr_pages += nr_pages;
1376                        return 0;
1377                }
1378        }
1379
1380        /*
1381         * No merge.  Insert a new extent, preserving ordering.
1382         */
1383        new_se = kmalloc(sizeof(*se), GFP_KERNEL);
1384        if (new_se == NULL)
1385                return -ENOMEM;
1386        new_se->start_page = start_page;
1387        new_se->nr_pages = nr_pages;
1388        new_se->start_block = start_block;
1389
1390        list_add_tail(&new_se->list, &sis->first_swap_extent.list);
1391        return 1;
1392}
1393
1394/*
1395 * A `swap extent' is a simple thing which maps a contiguous range of pages
1396 * onto a contiguous range of disk blocks.  An ordered list of swap extents
1397 * is built at swapon time and is then used at swap_writepage/swap_readpage
1398 * time for locating where on disk a page belongs.
1399 *
1400 * If the swapfile is an S_ISBLK block device, a single extent is installed.
1401 * This is done so that the main operating code can treat S_ISBLK and S_ISREG
1402 * swap files identically.
1403 *
1404 * Whether the swapdev is an S_ISREG file or an S_ISBLK blockdev, the swap
1405 * extent list operates in PAGE_SIZE disk blocks.  Both S_ISREG and S_ISBLK
1406 * swapfiles are handled *identically* after swapon time.
1407 *
1408 * For S_ISREG swapfiles, setup_swap_extents() will walk all the file's blocks
1409 * and will parse them into an ordered extent list, in PAGE_SIZE chunks.  If
1410 * some stray blocks are found which do not fall within the PAGE_SIZE alignment
1411 * requirements, they are simply tossed out - we will never use those blocks
1412 * for swapping.
1413 *
1414 * For S_ISREG swapfiles we set S_SWAPFILE across the life of the swapon.  This
1415 * prevents root from shooting her foot off by ftruncating an in-use swapfile,
1416 * which will scribble on the fs.
1417 *
1418 * The amount of disk space which a single swap extent represents varies.
1419 * Typically it is in the 1-4 megabyte range.  So we can have hundreds of
1420 * extents in the list.  To avoid much list walking, we cache the previous
1421 * search location in `curr_swap_extent', and start new searches from there.
1422 * This is extremely effective.  The average number of iterations in
1423 * map_swap_page() has been measured at about 0.3 per page.  - akpm.
1424 */
1425static int setup_swap_extents(struct swap_info_struct *sis, sector_t *span)
1426{
1427        struct inode *inode;
1428        unsigned blocks_per_page;
1429        unsigned long page_no;
1430        unsigned blkbits;
1431        sector_t probe_block;
1432        sector_t last_block;
1433        sector_t lowest_block = -1;
1434        sector_t highest_block = 0;
1435        int nr_extents = 0;
1436        int ret;
1437
1438        inode = sis->swap_file->f_mapping->host;
1439        if (S_ISBLK(inode->i_mode)) {
1440                ret = add_swap_extent(sis, 0, sis->max, 0);
1441                *span = sis->pages;
1442                goto out;
1443        }
1444
1445        blkbits = inode->i_blkbits;
1446        blocks_per_page = PAGE_SIZE >> blkbits;
1447
1448        /*
1449         * Map all the blocks into the extent list.  This code doesn't try
1450         * to be very smart.
1451         */
1452        probe_block = 0;
1453        page_no = 0;
1454        last_block = i_size_read(inode) >> blkbits;
1455        while ((probe_block + blocks_per_page) <= last_block &&
1456                        page_no < sis->max) {
1457                unsigned block_in_page;
1458                sector_t first_block;
1459
1460                first_block = bmap(inode, probe_block);
1461                if (first_block == 0)
1462                        goto bad_bmap;
1463
1464                /*
1465                 * It must be PAGE_SIZE aligned on-disk
1466                 */
1467                if (first_block & (blocks_per_page - 1)) {
1468                        probe_block++;
1469                        goto reprobe;
1470                }
1471
1472                for (block_in_page = 1; block_in_page < blocks_per_page;
1473                                        block_in_page++) {
1474                        sector_t block;
1475
1476                        block = bmap(inode, probe_block + block_in_page);
1477                        if (block == 0)
1478                                goto bad_bmap;
1479                        if (block != first_block + block_in_page) {
1480                                /* Discontiguity */
1481                                probe_block++;
1482                                goto reprobe;
1483                        }
1484                }
1485
1486                first_block >>= (PAGE_SHIFT - blkbits);
1487                if (page_no) {  /* exclude the header page */
1488                        if (first_block < lowest_block)
1489                                lowest_block = first_block;
1490                        if (first_block > highest_block)
1491                                highest_block = first_block;
1492                }
1493
1494                /*
1495                 * We found a PAGE_SIZE-length, PAGE_SIZE-aligned run of blocks
1496                 */
1497                ret = add_swap_extent(sis, page_no, 1, first_block);
1498                if (ret < 0)
1499                        goto out;
1500                nr_extents += ret;
1501                page_no++;
1502                probe_block += blocks_per_page;
1503reprobe:
1504                continue;
1505        }
1506        ret = nr_extents;
1507        *span = 1 + highest_block - lowest_block;
1508        if (page_no == 0)
1509                page_no = 1;    /* force Empty message */
1510        sis->max = page_no;
1511        sis->pages = page_no - 1;
1512        sis->highest_bit = page_no - 1;
1513out:
1514        return ret;
1515bad_bmap:
1516        printk(KERN_ERR "swapon: swapfile has holes\n");
1517        ret = -EINVAL;
1518        goto out;
1519}
1520
1521static void enable_swap_info(struct swap_info_struct *p, int prio,
1522                                unsigned char *swap_map)
1523{
1524        int i, prev;
1525
1526        spin_lock(&swap_lock);
1527        if (prio >= 0)
1528                p->prio = prio;
1529        else
1530                p->prio = --least_priority;
1531        p->swap_map = swap_map;
1532        p->flags |= SWP_WRITEOK;
1533        nr_swap_pages += p->pages;
1534        total_swap_pages += p->pages;
1535
1536        /* insert swap space into swap_list: */
1537        prev = -1;
1538        for (i = swap_list.head; i >= 0; i = swap_info[i]->next) {
1539                if (p->prio >= swap_info[i]->prio)
1540                        break;
1541                prev = i;
1542        }
1543        p->next = i;
1544        if (prev < 0)
1545                swap_list.head = swap_list.next = p->type;
1546        else
1547                swap_info[prev]->next = p->type;
1548        spin_unlock(&swap_lock);
1549}
1550
1551SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
1552{
1553        struct swap_info_struct *p = NULL;
1554        unsigned char *swap_map;
1555        struct file *swap_file, *victim;
1556        struct address_space *mapping;
1557        struct inode *inode;
1558        char *pathname;
1559        int oom_score_adj;
1560        int i, type, prev;
1561        int err;
1562
1563        if (!capable(CAP_SYS_ADMIN))
1564                return -EPERM;
1565
1566        pathname = getname(specialfile);
1567        err = PTR_ERR(pathname);
1568        if (IS_ERR(pathname))
1569                goto out;
1570
1571        victim = filp_open(pathname, O_RDWR|O_LARGEFILE, 0);
1572        putname(pathname);
1573        err = PTR_ERR(victim);
1574        if (IS_ERR(victim))
1575                goto out;
1576
1577        mapping = victim->f_mapping;
1578        prev = -1;
1579        spin_lock(&swap_lock);
1580        for (type = swap_list.head; type >= 0; type = swap_info[type]->next) {
1581                p = swap_info[type];
1582                if (p->flags & SWP_WRITEOK) {
1583                        if (p->swap_file->f_mapping == mapping)
1584                                break;
1585                }
1586                prev = type;
1587        }
1588        if (type < 0) {
1589                err = -EINVAL;
1590                spin_unlock(&swap_lock);
1591                goto out_dput;
1592        }
1593        if (!security_vm_enough_memory(p->pages))
1594                vm_unacct_memory(p->pages);
1595        else {
1596                err = -ENOMEM;
1597                spin_unlock(&swap_lock);
1598                goto out_dput;
1599        }
1600        if (prev < 0)
1601                swap_list.head = p->next;
1602        else
1603                swap_info[prev]->next = p->next;
1604        if (type == swap_list.next) {
1605                /* just pick something that's safe... */
1606                swap_list.next = swap_list.head;
1607        }
1608        if (p->prio < 0) {
1609                for (i = p->next; i >= 0; i = swap_info[i]->next)
1610                        swap_info[i]->prio = p->prio--;
1611                least_priority++;
1612        }
1613        nr_swap_pages -= p->pages;
1614        total_swap_pages -= p->pages;
1615        p->flags &= ~SWP_WRITEOK;
1616        spin_unlock(&swap_lock);
1617
1618        oom_score_adj = test_set_oom_score_adj(OOM_SCORE_ADJ_MAX);
1619        err = try_to_unuse(type);
1620        test_set_oom_score_adj(oom_score_adj);
1621
1622        if (err) {
1623                /*
1624                 * reading p->prio and p->swap_map outside the lock is
1625                 * safe here because only sys_swapon and sys_swapoff
1626                 * change them, and there can be no other sys_swapon or
1627                 * sys_swapoff for this swap_info_struct at this point.
1628                 */
1629                /* re-insert swap space back into swap_list */
1630                enable_swap_info(p, p->prio, p->swap_map);
1631                goto out_dput;
1632        }
1633
1634        destroy_swap_extents(p);
1635        if (p->flags & SWP_CONTINUED)
1636                free_swap_count_continuations(p);
1637
1638        mutex_lock(&swapon_mutex);
1639        spin_lock(&swap_lock);
1640        drain_mmlist();
1641
1642        /* wait for anyone still in scan_swap_map */
1643        p->highest_bit = 0;             /* cuts scans short */
1644        while (p->flags >= SWP_SCANNING) {
1645                spin_unlock(&swap_lock);
1646                schedule_timeout_uninterruptible(1);
1647                spin_lock(&swap_lock);
1648        }
1649
1650        swap_file = p->swap_file;
1651        p->swap_file = NULL;
1652        p->max = 0;
1653        swap_map = p->swap_map;
1654        p->swap_map = NULL;
1655        p->flags = 0;
1656        spin_unlock(&swap_lock);
1657        mutex_unlock(&swapon_mutex);
1658        vfree(swap_map);
1659        /* Destroy swap account informatin */
1660        swap_cgroup_swapoff(type);
1661
1662        inode = mapping->host;
1663        if (S_ISBLK(inode->i_mode)) {
1664                struct block_device *bdev = I_BDEV(inode);
1665                set_blocksize(bdev, p->old_block_size);
1666                blkdev_put(bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL);
1667        } else {
1668                mutex_lock(&inode->i_mutex);
1669                inode->i_flags &= ~S_SWAPFILE;
1670                mutex_unlock(&inode->i_mutex);
1671        }
1672        filp_close(swap_file, NULL);
1673        err = 0;
1674        atomic_inc(&proc_poll_event);
1675        wake_up_interruptible(&proc_poll_wait);
1676
1677out_dput:
1678        filp_close(victim, NULL);
1679out:
1680        return err;
1681}
1682
1683#ifdef CONFIG_PROC_FS
1684static unsigned swaps_poll(struct file *file, poll_table *wait)
1685{
1686        struct seq_file *seq = file->private_data;
1687
1688        poll_wait(file, &proc_poll_wait, wait);
1689
1690        if (seq->poll_event != atomic_read(&proc_poll_event)) {
1691                seq->poll_event = atomic_read(&proc_poll_event);
1692                return POLLIN | POLLRDNORM | POLLERR | POLLPRI;
1693        }
1694
1695        return POLLIN | POLLRDNORM;
1696}
1697
1698/* iterator */
1699static void *swap_start(struct seq_file *swap, loff_t *pos)
1700{
1701        struct swap_info_struct *si;
1702        int type;
1703        loff_t l = *pos;
1704
1705        mutex_lock(&swapon_mutex);
1706
1707        if (!l)
1708                return SEQ_START_TOKEN;
1709
1710        for (type = 0; type < nr_swapfiles; type++) {
1711                smp_rmb();      /* read nr_swapfiles before swap_info[type] */
1712                si = swap_info[type];
1713                if (!(si->flags & SWP_USED) || !si->swap_map)
1714                        continue;
1715                if (!--l)
1716                        return si;
1717        }
1718
1719        return NULL;
1720}
1721
1722static void *swap_next(struct seq_file *swap, void *v, loff_t *pos)
1723{
1724        struct swap_info_struct *si = v;
1725        int type;
1726
1727        if (v == SEQ_START_TOKEN)
1728                type = 0;
1729        else
1730                type = si->type + 1;
1731
1732        for (; type < nr_swapfiles; type++) {
1733                smp_rmb();      /* read nr_swapfiles before swap_info[type] */
1734                si = swap_info[type];
1735                if (!(si->flags & SWP_USED) || !si->swap_map)
1736                        continue;
1737                ++*pos;
1738                return si;
1739        }
1740
1741        return NULL;
1742}
1743
1744static void swap_stop(struct seq_file *swap, void *v)
1745{
1746        mutex_unlock(&swapon_mutex);
1747}
1748
1749static int swap_show(struct seq_file *swap, void *v)
1750{
1751        struct swap_info_struct *si = v;
1752        struct file *file;
1753        int len;
1754
1755        if (si == SEQ_START_TOKEN) {
1756                seq_puts(swap,"Filename\t\t\t\tType\t\tSize\tUsed\tPriority\n");
1757                return 0;
1758        }
1759
1760        file = si->swap_file;
1761        len = seq_path(swap, &file->f_path, " \t\n\\");
1762        seq_printf(swap, "%*s%s\t%u\t%u\t%d\n",
1763                        len < 40 ? 40 - len : 1, " ",
1764                        S_ISBLK(file->f_path.dentry->d_inode->i_mode) ?
1765                                "partition" : "file\t",
1766                        si->pages << (PAGE_SHIFT - 10),
1767                        si->inuse_pages << (PAGE_SHIFT - 10),
1768                        si->prio);
1769        return 0;
1770}
1771
1772static const struct seq_operations swaps_op = {
1773        .start =        swap_start,
1774        .next =         swap_next,
1775        .stop =         swap_stop,
1776        .show =         swap_show
1777};
1778
1779static int swaps_open(struct inode *inode, struct file *file)
1780{
1781        struct seq_file *seq;
1782        int ret;
1783
1784        ret = seq_open(file, &swaps_op);
1785        if (ret)
1786                return ret;
1787
1788        seq = file->private_data;
1789        seq->poll_event = atomic_read(&proc_poll_event);
1790        return 0;
1791}
1792
1793static const struct file_operations proc_swaps_operations = {
1794        .open           = swaps_open,
1795        .read           = seq_read,
1796        .llseek         = seq_lseek,
1797        .release        = seq_release,
1798        .poll           = swaps_poll,
1799};
1800
1801static int __init procswaps_init(void)
1802{
1803        proc_create("swaps", 0, NULL, &proc_swaps_operations);
1804        return 0;
1805}
1806__initcall(procswaps_init);
1807#endif /* CONFIG_PROC_FS */
1808
1809#ifdef MAX_SWAPFILES_CHECK
1810static int __init max_swapfiles_check(void)
1811{
1812        MAX_SWAPFILES_CHECK();
1813        return 0;
1814}
1815late_initcall(max_swapfiles_check);
1816#endif
1817
1818static struct swap_info_struct *alloc_swap_info(void)
1819{
1820        struct swap_info_struct *p;
1821        unsigned int type;
1822
1823        p = kzalloc(sizeof(*p), GFP_KERNEL);
1824        if (!p)
1825                return ERR_PTR(-ENOMEM);
1826
1827        spin_lock(&swap_lock);
1828        for (type = 0; type < nr_swapfiles; type++) {
1829                if (!(swap_info[type]->flags & SWP_USED))
1830                        break;
1831        }
1832        if (type >= MAX_SWAPFILES) {
1833                spin_unlock(&swap_lock);
1834                kfree(p);
1835                return ERR_PTR(-EPERM);
1836        }
1837        if (type >= nr_swapfiles) {
1838                p->type = type;
1839                swap_info[type] = p;
1840                /*
1841                 * Write swap_info[type] before nr_swapfiles, in case a
1842                 * racing procfs swap_start() or swap_next() is reading them.
1843                 * (We never shrink nr_swapfiles, we never free this entry.)
1844                 */
1845                smp_wmb();
1846                nr_swapfiles++;
1847        } else {
1848                kfree(p);
1849                p = swap_info[type];
1850                /*
1851                 * Do not memset this entry: a racing procfs swap_next()
1852                 * would be relying on p->type to remain valid.
1853                 */
1854        }
1855        INIT_LIST_HEAD(&p->first_swap_extent.list);
1856        p->flags = SWP_USED;
1857        p->next = -1;
1858        spin_unlock(&swap_lock);
1859
1860        return p;
1861}
1862
1863static int claim_swapfile(struct swap_info_struct *p, struct inode *inode)
1864{
1865        int error;
1866
1867        if (S_ISBLK(inode->i_mode)) {
1868                p->bdev = bdgrab(I_BDEV(inode));
1869                error = blkdev_get(p->bdev,
1870                                   FMODE_READ | FMODE_WRITE | FMODE_EXCL,
1871                                   sys_swapon);
1872                if (error < 0) {
1873                        p->bdev = NULL;
1874                        return -EINVAL;
1875                }
1876                p->old_block_size = block_size(p->bdev);
1877                error = set_blocksize(p->bdev, PAGE_SIZE);
1878                if (error < 0)
1879                        return error;
1880                p->flags |= SWP_BLKDEV;
1881        } else if (S_ISREG(inode->i_mode)) {
1882                p->bdev = inode->i_sb->s_bdev;
1883                mutex_lock(&inode->i_mutex);
1884                if (IS_SWAPFILE(inode))
1885                        return -EBUSY;
1886        } else
1887                return -EINVAL;
1888
1889        return 0;
1890}
1891
1892static unsigned long read_swap_header(struct swap_info_struct *p,
1893                                        union swap_header *swap_header,
1894                                        struct inode *inode)
1895{
1896        int i;
1897        unsigned long maxpages;
1898        unsigned long swapfilepages;
1899
1900        if (memcmp("SWAPSPACE2", swap_header->magic.magic, 10)) {
1901                printk(KERN_ERR "Unable to find swap-space signature\n");
1902                return 0;
1903        }
1904
1905        /* swap partition endianess hack... */
1906        if (swab32(swap_header->info.version) == 1) {
1907                swab32s(&swap_header->info.version);
1908                swab32s(&swap_header->info.last_page);
1909                swab32s(&swap_header->info.nr_badpages);
1910                for (i = 0; i < swap_header->info.nr_badpages; i++)
1911                        swab32s(&swap_header->info.badpages[i]);
1912        }
1913        /* Check the swap header's sub-version */
1914        if (swap_header->info.version != 1) {
1915                printk(KERN_WARNING
1916                       "Unable to handle swap header version %d\n",
1917                       swap_header->info.version);
1918                return 0;
1919        }
1920
1921        p->lowest_bit  = 1;
1922        p->cluster_next = 1;
1923        p->cluster_nr = 0;
1924
1925        /*
1926         * Find out how many pages are allowed for a single swap
1927         * device. There are three limiting factors: 1) the number
1928         * of bits for the swap offset in the swp_entry_t type, and
1929         * 2) the number of bits in the swap pte as defined by the
1930         * the different architectures, and 3) the number of free bits
1931         * in an exceptional radix_tree entry. In order to find the
1932         * largest possible bit mask, a swap entry with swap type 0
1933         * and swap offset ~0UL is created, encoded to a swap pte,
1934         * decoded to a swp_entry_t again, and finally the swap
1935         * offset is extracted. This will mask all the bits from
1936         * the initial ~0UL mask that can't be encoded in either
1937         * the swp_entry_t or the architecture definition of a
1938         * swap pte.  Then the same is done for a radix_tree entry.
1939         */
1940        maxpages = swp_offset(pte_to_swp_entry(
1941                        swp_entry_to_pte(swp_entry(0, ~0UL))));
1942        maxpages = swp_offset(radix_to_swp_entry(
1943                        swp_to_radix_entry(swp_entry(0, maxpages)))) + 1;
1944
1945        if (maxpages > swap_header->info.last_page) {
1946                maxpages = swap_header->info.last_page + 1;
1947                /* p->max is an unsigned int: don't overflow it */
1948                if ((unsigned int)maxpages == 0)
1949                        maxpages = UINT_MAX;
1950        }
1951        p->highest_bit = maxpages - 1;
1952
1953        if (!maxpages)
1954                return 0;
1955        swapfilepages = i_size_read(inode) >> PAGE_SHIFT;
1956        if (swapfilepages && maxpages > swapfilepages) {
1957                printk(KERN_WARNING
1958                       "Swap area shorter than signature indicates\n");
1959                return 0;
1960        }
1961        if (swap_header->info.nr_badpages && S_ISREG(inode->i_mode))
1962                return 0;
1963        if (swap_header->info.nr_badpages > MAX_SWAP_BADPAGES)
1964                return 0;
1965
1966        return maxpages;
1967}
1968
1969static int setup_swap_map_and_extents(struct swap_info_struct *p,
1970                                        union swap_header *swap_header,
1971                                        unsigned char *swap_map,
1972                                        unsigned long maxpages,
1973                                        sector_t *span)
1974{
1975        int i;
1976        unsigned int nr_good_pages;
1977        int nr_extents;
1978
1979        nr_good_pages = maxpages - 1;   /* omit header page */
1980
1981        for (i = 0; i < swap_header->info.nr_badpages; i++) {
1982                unsigned int page_nr = swap_header->info.badpages[i];
1983                if (page_nr == 0 || page_nr > swap_header->info.last_page)
1984                        return -EINVAL;
1985                if (page_nr < maxpages) {
1986                        swap_map[page_nr] = SWAP_MAP_BAD;
1987                        nr_good_pages--;
1988                }
1989        }
1990
1991        if (nr_good_pages) {
1992                swap_map[0] = SWAP_MAP_BAD;
1993                p->max = maxpages;
1994                p->pages = nr_good_pages;
1995                nr_extents = setup_swap_extents(p, span);
1996                if (nr_extents < 0)
1997                        return nr_extents;
1998                nr_good_pages = p->pages;
1999        }
2000        if (!nr_good_pages) {
2001                printk(KERN_WARNING "Empty swap-file\n");
2002                return -EINVAL;
2003        }
2004
2005        return nr_extents;
2006}
2007
2008SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
2009{
2010        struct swap_info_struct *p;
2011        char *name;
2012        struct file *swap_file = NULL;
2013        struct address_space *mapping;
2014        int i;
2015        int prio;
2016        int error;
2017        union swap_header *swap_header;
2018        int nr_extents;
2019        sector_t span;
2020        unsigned long maxpages;
2021        unsigned char *swap_map = NULL;
2022        struct page *page = NULL;
2023        struct inode *inode = NULL;
2024
2025        if (!capable(CAP_SYS_ADMIN))
2026                return -EPERM;
2027
2028        p = alloc_swap_info();
2029        if (IS_ERR(p))
2030                return PTR_ERR(p);
2031
2032        name = getname(specialfile);
2033        if (IS_ERR(name)) {
2034                error = PTR_ERR(name);
2035                name = NULL;
2036                goto bad_swap;
2037        }
2038        swap_file = filp_open(name, O_RDWR|O_LARGEFILE, 0);
2039        if (IS_ERR(swap_file)) {
2040                error = PTR_ERR(swap_file);
2041                swap_file = NULL;
2042                goto bad_swap;
2043        }
2044
2045        p->swap_file = swap_file;
2046        mapping = swap_file->f_mapping;
2047
2048        for (i = 0; i < nr_swapfiles; i++) {
2049                struct swap_info_struct *q = swap_info[i];
2050
2051                if (q == p || !q->swap_file)
2052                        continue;
2053                if (mapping == q->swap_file->f_mapping) {
2054                        error = -EBUSY;
2055                        goto bad_swap;
2056                }
2057        }
2058
2059        inode = mapping->host;
2060        /* If S_ISREG(inode->i_mode) will do mutex_lock(&inode->i_mutex); */
2061        error = claim_swapfile(p, inode);
2062        if (unlikely(error))
2063                goto bad_swap;
2064
2065        /*
2066         * Read the swap header.
2067         */
2068        if (!mapping->a_ops->readpage) {
2069                error = -EINVAL;
2070                goto bad_swap;
2071        }
2072        page = read_mapping_page(mapping, 0, swap_file);
2073        if (IS_ERR(page)) {
2074                error = PTR_ERR(page);
2075                goto bad_swap;
2076        }
2077        swap_header = kmap(page);
2078
2079        maxpages = read_swap_header(p, swap_header, inode);
2080        if (unlikely(!maxpages)) {
2081                error = -EINVAL;
2082                goto bad_swap;
2083        }
2084
2085        /* OK, set up the swap map and apply the bad block list */
2086        swap_map = vzalloc(maxpages);
2087        if (!swap_map) {
2088                error = -ENOMEM;
2089                goto bad_swap;
2090        }
2091
2092        error = swap_cgroup_swapon(p->type, maxpages);
2093        if (error)
2094                goto bad_swap;
2095
2096        nr_extents = setup_swap_map_and_extents(p, swap_header, swap_map,
2097                maxpages, &span);
2098        if (unlikely(nr_extents < 0)) {
2099                error = nr_extents;
2100                goto bad_swap;
2101        }
2102
2103        if (p->bdev) {
2104                if (blk_queue_nonrot(bdev_get_queue(p->bdev))) {
2105                        p->flags |= SWP_SOLIDSTATE;
2106                        p->cluster_next = 1 + (random32() % p->highest_bit);
2107                }
2108                if (discard_swap(p) == 0 && (swap_flags & SWAP_FLAG_DISCARD))
2109                        p->flags |= SWP_DISCARDABLE;
2110        }
2111
2112        mutex_lock(&swapon_mutex);
2113        prio = -1;
2114        if (swap_flags & SWAP_FLAG_PREFER)
2115                prio =
2116                  (swap_flags & SWAP_FLAG_PRIO_MASK) >> SWAP_FLAG_PRIO_SHIFT;
2117        enable_swap_info(p, prio, swap_map);
2118
2119        printk(KERN_INFO "Adding %uk swap on %s.  "
2120                        "Priority:%d extents:%d across:%lluk %s%s\n",
2121                p->pages<<(PAGE_SHIFT-10), name, p->prio,
2122                nr_extents, (unsigned long long)span<<(PAGE_SHIFT-10),
2123                (p->flags & SWP_SOLIDSTATE) ? "SS" : "",
2124                (p->flags & SWP_DISCARDABLE) ? "D" : "");
2125
2126        mutex_unlock(&swapon_mutex);
2127        atomic_inc(&proc_poll_event);
2128        wake_up_interruptible(&proc_poll_wait);
2129
2130        if (S_ISREG(inode->i_mode))
2131                inode->i_flags |= S_SWAPFILE;
2132        error = 0;
2133        goto out;
2134bad_swap:
2135        if (inode && S_ISBLK(inode->i_mode) && p->bdev) {
2136                set_blocksize(p->bdev, p->old_block_size);
2137                blkdev_put(p->bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL);
2138        }
2139        destroy_swap_extents(p);
2140        swap_cgroup_swapoff(p->type);
2141        spin_lock(&swap_lock);
2142        p->swap_file = NULL;
2143        p->flags = 0;
2144        spin_unlock(&swap_lock);
2145        vfree(swap_map);
2146        if (swap_file) {
2147                if (inode && S_ISREG(inode->i_mode)) {
2148                        mutex_unlock(&inode->i_mutex);
2149                        inode = NULL;
2150                }
2151                filp_close(swap_file, NULL);
2152        }
2153out:
2154        if (page && !IS_ERR(page)) {
2155                kunmap(page);
2156                page_cache_release(page);
2157        }
2158        if (name)
2159                putname(name);
2160        if (inode && S_ISREG(inode->i_mode))
2161                mutex_unlock(&inode->i_mutex);
2162        return error;
2163}
2164
2165void si_swapinfo(struct sysinfo *val)
2166{
2167        unsigned int type;
2168        unsigned long nr_to_be_unused = 0;
2169
2170        spin_lock(&swap_lock);
2171        for (type = 0; type < nr_swapfiles; type++) {
2172                struct swap_info_struct *si = swap_info[type];
2173
2174                if ((si->flags & SWP_USED) && !(si->flags & SWP_WRITEOK))
2175                        nr_to_be_unused += si->inuse_pages;
2176        }
2177        val->freeswap = nr_swap_pages + nr_to_be_unused;
2178        val->totalswap = total_swap_pages + nr_to_be_unused;
2179        spin_unlock(&swap_lock);
2180}
2181
2182/*
2183 * Verify that a swap entry is valid and increment its swap map count.
2184 *
2185 * Returns error code in following case.
2186 * - success -> 0
2187 * - swp_entry is invalid -> EINVAL
2188 * - swp_entry is migration entry -> EINVAL
2189 * - swap-cache reference is requested but there is already one. -> EEXIST
2190 * - swap-cache reference is requested but the entry is not used. -> ENOENT
2191 * - swap-mapped reference requested but needs continued swap count. -> ENOMEM
2192 */
2193static int __swap_duplicate(swp_entry_t entry, unsigned char usage)
2194{
2195        struct swap_info_struct *p;
2196        unsigned long offset, type;
2197        unsigned char count;
2198        unsigned char has_cache;
2199        int err = -EINVAL;
2200
2201        if (non_swap_entry(entry))
2202                goto out;
2203
2204        type = swp_type(entry);
2205        if (type >= nr_swapfiles)
2206                goto bad_file;
2207        p = swap_info[type];
2208        offset = swp_offset(entry);
2209
2210        spin_lock(&swap_lock);
2211        if (unlikely(offset >= p->max))
2212                goto unlock_out;
2213
2214        count = p->swap_map[offset];
2215        has_cache = count & SWAP_HAS_CACHE;
2216        count &= ~SWAP_HAS_CACHE;
2217        err = 0;
2218
2219        if (usage == SWAP_HAS_CACHE) {
2220
2221                /* set SWAP_HAS_CACHE if there is no cache and entry is used */
2222                if (!has_cache && count)
2223                        has_cache = SWAP_HAS_CACHE;
2224                else if (has_cache)             /* someone else added cache */
2225                        err = -EEXIST;
2226                else                            /* no users remaining */
2227                        err = -ENOENT;
2228
2229        } else if (count || has_cache) {
2230
2231                if ((count & ~COUNT_CONTINUED) < SWAP_MAP_MAX)
2232                        count += usage;
2233                else if ((count & ~COUNT_CONTINUED) > SWAP_MAP_MAX)
2234                        err = -EINVAL;
2235                else if (swap_count_continued(p, offset, count))
2236                        count = COUNT_CONTINUED;
2237                else
2238                        err = -ENOMEM;
2239        } else
2240                err = -ENOENT;                  /* unused swap entry */
2241
2242        p->swap_map[offset] = count | has_cache;
2243
2244unlock_out:
2245        spin_unlock(&swap_lock);
2246out:
2247        return err;
2248
2249bad_file:
2250        printk(KERN_ERR "swap_dup: %s%08lx\n", Bad_file, entry.val);
2251        goto out;
2252}
2253
2254/*
2255 * Help swapoff by noting that swap entry belongs to shmem/tmpfs
2256 * (in which case its reference count is never incremented).
2257 */
2258void swap_shmem_alloc(swp_entry_t entry)
2259{
2260        __swap_duplicate(entry, SWAP_MAP_SHMEM);
2261}
2262
2263/*
2264 * Increase reference count of swap entry by 1.
2265 * Returns 0 for success, or -ENOMEM if a swap_count_continuation is required
2266 * but could not be atomically allocated.  Returns 0, just as if it succeeded,
2267 * if __swap_duplicate() fails for another reason (-EINVAL or -ENOENT), which
2268 * might occur if a page table entry has got corrupted.
2269 */
2270int swap_duplicate(swp_entry_t entry)
2271{
2272        int err = 0;
2273
2274        while (!err && __swap_duplicate(entry, 1) == -ENOMEM)
2275                err = add_swap_count_continuation(entry, GFP_ATOMIC);
2276        return err;
2277}
2278
2279/*
2280 * @entry: swap entry for which we allocate swap cache.
2281 *
2282 * Called when allocating swap cache for existing swap entry,
2283 * This can return error codes. Returns 0 at success.
2284 * -EBUSY means there is a swap cache.
2285 * Note: return code is different from swap_duplicate().
2286 */
2287int swapcache_prepare(swp_entry_t entry)
2288{
2289        return __swap_duplicate(entry, SWAP_HAS_CACHE);
2290}
2291
2292/*
2293 * swap_lock prevents swap_map being freed. Don't grab an extra
2294 * reference on the swaphandle, it doesn't matter if it becomes unused.
2295 */
2296int valid_swaphandles(swp_entry_t entry, unsigned long *offset)
2297{
2298        struct swap_info_struct *si;
2299        int our_page_cluster = page_cluster;
2300        pgoff_t target, toff;
2301        pgoff_t base, end;
2302        int nr_pages = 0;
2303
2304        if (!our_page_cluster)  /* no readahead */
2305                return 0;
2306
2307        si = swap_info[swp_type(entry)];
2308        target = swp_offset(entry);
2309        base = (target >> our_page_cluster) << our_page_cluster;
2310        end = base + (1 << our_page_cluster);
2311        if (!base)              /* first page is swap header */
2312                base++;
2313
2314        spin_lock(&swap_lock);
2315        if (end > si->max)      /* don't go beyond end of map */
2316                end = si->max;
2317
2318        /* Count contiguous allocated slots above our target */
2319        for (toff = target; ++toff < end; nr_pages++) {
2320                /* Don't read in free or bad pages */
2321                if (!si->swap_map[toff])
2322                        break;
2323                if (swap_count(si->swap_map[toff]) == SWAP_MAP_BAD)
2324                        break;
2325        }
2326        /* Count contiguous allocated slots below our target */
2327        for (toff = target; --toff >= base; nr_pages++) {
2328                /* Don't read in free or bad pages */
2329                if (!si->swap_map[toff])
2330                        break;
2331                if (swap_count(si->swap_map[toff]) == SWAP_MAP_BAD)
2332                        break;
2333        }
2334        spin_unlock(&swap_lock);
2335
2336        /*
2337         * Indicate starting offset, and return number of pages to get:
2338         * if only 1, say 0, since there's then no readahead to be done.
2339         */
2340        *offset = ++toff;
2341        return nr_pages? ++nr_pages: 0;
2342}
2343
2344/*
2345 * add_swap_count_continuation - called when a swap count is duplicated
2346 * beyond SWAP_MAP_MAX, it allocates a new page and links that to the entry's
2347 * page of the original vmalloc'ed swap_map, to hold the continuation count
2348 * (for that entry and for its neighbouring PAGE_SIZE swap entries).  Called
2349 * again when count is duplicated beyond SWAP_MAP_MAX * SWAP_CONT_MAX, etc.
2350 *
2351 * These continuation pages are seldom referenced: the common paths all work
2352 * on the original swap_map, only referring to a continuation page when the
2353 * low "digit" of a count is incremented or decremented through SWAP_MAP_MAX.
2354 *
2355 * add_swap_count_continuation(, GFP_ATOMIC) can be called while holding
2356 * page table locks; if it fails, add_swap_count_continuation(, GFP_KERNEL)
2357 * can be called after dropping locks.
2358 */
2359int add_swap_count_continuation(swp_entry_t entry, gfp_t gfp_mask)
2360{
2361        struct swap_info_struct *si;
2362        struct page *head;
2363        struct page *page;
2364        struct page *list_page;
2365        pgoff_t offset;
2366        unsigned char count;
2367
2368        /*
2369         * When debugging, it's easier to use __GFP_ZERO here; but it's better
2370         * for latency not to zero a page while GFP_ATOMIC and holding locks.
2371         */
2372        page = alloc_page(gfp_mask | __GFP_HIGHMEM);
2373
2374        si = swap_info_get(entry);
2375        if (!si) {
2376                /*
2377                 * An acceptable race has occurred since the failing
2378                 * __swap_duplicate(): the swap entry has been freed,
2379                 * perhaps even the whole swap_map cleared for swapoff.
2380                 */
2381                goto outer;
2382        }
2383
2384        offset = swp_offset(entry);
2385        count = si->swap_map[offset] & ~SWAP_HAS_CACHE;
2386
2387        if ((count & ~COUNT_CONTINUED) != SWAP_MAP_MAX) {
2388                /*
2389                 * The higher the swap count, the more likely it is that tasks
2390                 * will race to add swap count continuation: we need to avoid
2391                 * over-provisioning.
2392                 */
2393                goto out;
2394        }
2395
2396        if (!page) {
2397                spin_unlock(&swap_lock);
2398                return -ENOMEM;
2399        }
2400
2401        /*
2402         * We are fortunate that although vmalloc_to_page uses pte_offset_map,
2403         * no architecture is using highmem pages for kernel pagetables: so it
2404         * will not corrupt the GFP_ATOMIC caller's atomic pagetable kmaps.
2405         */
2406        head = vmalloc_to_page(si->swap_map + offset);
2407        offset &= ~PAGE_MASK;
2408
2409        /*
2410         * Page allocation does not initialize the page's lru field,
2411         * but it does always reset its private field.
2412         */
2413        if (!page_private(head)) {
2414                BUG_ON(count & COUNT_CONTINUED);
2415                INIT_LIST_HEAD(&head->lru);
2416                set_page_private(head, SWP_CONTINUED);
2417                si->flags |= SWP_CONTINUED;
2418        }
2419
2420        list_for_each_entry(list_page, &head->lru, lru) {
2421                unsigned char *map;
2422
2423                /*
2424                 * If the previous map said no continuation, but we've found
2425                 * a continuation page, free our allocation and use this one.
2426                 */
2427                if (!(count & COUNT_CONTINUED))
2428                        goto out;
2429
2430                map = kmap_atomic(list_page, KM_USER0) + offset;
2431                count = *map;
2432                kunmap_atomic(map, KM_USER0);
2433
2434                /*
2435                 * If this continuation count now has some space in it,
2436                 * free our allocation and use this one.
2437                 */
2438                if ((count & ~COUNT_CONTINUED) != SWAP_CONT_MAX)
2439                        goto out;
2440        }
2441
2442        list_add_tail(&page->lru, &head->lru);
2443        page = NULL;                    /* now it's attached, don't free it */
2444out:
2445        spin_unlock(&swap_lock);
2446outer:
2447        if (page)
2448                __free_page(page);
2449        return 0;
2450}
2451
2452/*
2453 * swap_count_continued - when the original swap_map count is incremented
2454 * from SWAP_MAP_MAX, check if there is already a continuation page to carry
2455 * into, carry if so, or else fail until a new continuation page is allocated;
2456 * when the original swap_map count is decremented from 0 with continuation,
2457 * borrow from the continuation and report whether it still holds more.
2458 * Called while __swap_duplicate() or swap_entry_free() holds swap_lock.
2459 */
2460static bool swap_count_continued(struct swap_info_struct *si,
2461                                 pgoff_t offset, unsigned char count)
2462{
2463        struct page *head;
2464        struct page *page;
2465        unsigned char *map;
2466
2467        head = vmalloc_to_page(si->swap_map + offset);
2468        if (page_private(head) != SWP_CONTINUED) {
2469                BUG_ON(count & COUNT_CONTINUED);
2470                return false;           /* need to add count continuation */
2471        }
2472
2473        offset &= ~PAGE_MASK;
2474        page = list_entry(head->lru.next, struct page, lru);
2475        map = kmap_atomic(page, KM_USER0) + offset;
2476
2477        if (count == SWAP_MAP_MAX)      /* initial increment from swap_map */
2478                goto init_map;          /* jump over SWAP_CONT_MAX checks */
2479
2480        if (count == (SWAP_MAP_MAX | COUNT_CONTINUED)) { /* incrementing */
2481                /*
2482                 * Think of how you add 1 to 999
2483                 */
2484                while (*map == (SWAP_CONT_MAX | COUNT_CONTINUED)) {
2485                        kunmap_atomic(map, KM_USER0);
2486                        page = list_entry(page->lru.next, struct page, lru);
2487                        BUG_ON(page == head);
2488                        map = kmap_atomic(page, KM_USER0) + offset;
2489                }
2490                if (*map == SWAP_CONT_MAX) {
2491                        kunmap_atomic(map, KM_USER0);
2492                        page = list_entry(page->lru.next, struct page, lru);
2493                        if (page == head)
2494                                return false;   /* add count continuation */
2495                        map = kmap_atomic(page, KM_USER0) + offset;
2496init_map:               *map = 0;               /* we didn't zero the page */
2497                }
2498                *map += 1;
2499                kunmap_atomic(map, KM_USER0);
2500                page = list_entry(page->lru.prev, struct page, lru);
2501                while (page != head) {
2502                        map = kmap_atomic(page, KM_USER0) + offset;
2503                        *map = COUNT_CONTINUED;
2504                        kunmap_atomic(map, KM_USER0);
2505                        page = list_entry(page->lru.prev, struct page, lru);
2506                }
2507                return true;                    /* incremented */
2508
2509        } else {                                /* decrementing */
2510                /*
2511                 * Think of how you subtract 1 from 1000
2512                 */
2513                BUG_ON(count != COUNT_CONTINUED);
2514                while (*map == COUNT_CONTINUED) {
2515                        kunmap_atomic(map, KM_USER0);
2516                        page = list_entry(page->lru.next, struct page, lru);
2517                        BUG_ON(page == head);
2518                        map = kmap_atomic(page, KM_USER0) + offset;
2519                }
2520                BUG_ON(*map == 0);
2521                *map -= 1;
2522                if (*map == 0)
2523                        count = 0;
2524                kunmap_atomic(map, KM_USER0);
2525                page = list_entry(page->lru.prev, struct page, lru);
2526                while (page != head) {
2527                        map = kmap_atomic(page, KM_USER0) + offset;
2528                        *map = SWAP_CONT_MAX | count;
2529                        count = COUNT_CONTINUED;
2530                        kunmap_atomic(map, KM_USER0);
2531                        page = list_entry(page->lru.prev, struct page, lru);
2532                }
2533                return count == COUNT_CONTINUED;
2534        }
2535}
2536
2537/*
2538 * free_swap_count_continuations - swapoff free all the continuation pages
2539 * appended to the swap_map, after swap_map is quiesced, before vfree'ing it.
2540 */
2541static void free_swap_count_continuations(struct swap_info_struct *si)
2542{
2543        pgoff_t offset;
2544
2545        for (offset = 0; offset < si->max; offset += PAGE_SIZE) {
2546                struct page *head;
2547                head = vmalloc_to_page(si->swap_map + offset);
2548                if (page_private(head)) {
2549                        struct list_head *this, *next;
2550                        list_for_each_safe(this, next, &head->lru) {
2551                                struct page *page;
2552                                page = list_entry(this, struct page, lru);
2553                                list_del(this);
2554                                __free_page(page);
2555                        }
2556                }
2557        }
2558}
2559
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