mm/swap_state.c

   1 /*
   2  *  linux/mm/swap_state.c
   3  *
   4  *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
   5  *  Swap reorganised 29.12.95, Stephen Tweedie
   6  *
   7  *  Rewritten to use page cache, (C) 1998 Stephen Tweedie
   8  */
   9 #include <linux/mm.h>
  10 #include <linux/gfp.h>
  11 #include <linux/kernel_stat.h>
  12 #include <linux/swap.h>
  13 #include <linux/swapops.h>
  14 #include <linux/init.h>
  15 #include <linux/pagemap.h>
  16 #include <linux/backing-dev.h>
  17 #include <linux/blkdev.h>
  18 #include <linux/pagevec.h>
  19 #include <linux/migrate.h>
  20 #include <linux/vmalloc.h>
  21 #include <linux/swap_slots.h>
  22 #include <linux/huge_mm.h>
  23
  24 #include <asm/pgtable.h>
  25
  26 /*
  27  * swapper_space is a fiction, retained to simplify the path through
  28  * vmscan's shrink_page_list.
  29  */
  30 static const struct address_space_operations swap_aops = {
  31         .writepage      = swap_writepage,
  32         .set_page_dirty = swap_set_page_dirty,
  33 #ifdef CONFIG_MIGRATION
  34         .migratepage    = migrate_page,
  35 #endif
  36 };
  37
  38 struct address_space *swapper_spaces[MAX_SWAPFILES];
  39 static unsigned int nr_swapper_spaces[MAX_SWAPFILES];
  40 bool swap_vma_readahead = true;
  41
  42 #define SWAP_RA_WIN_SHIFT       (PAGE_SHIFT / 2)
  43 #define SWAP_RA_HITS_MASK       ((1UL << SWAP_RA_WIN_SHIFT) - 1)
  44 #define SWAP_RA_HITS_MAX        SWAP_RA_HITS_MASK
  45 #define SWAP_RA_WIN_MASK        (~PAGE_MASK & ~SWAP_RA_HITS_MASK)
  46
  47 #define SWAP_RA_HITS(v)         ((v) & SWAP_RA_HITS_MASK)
  48 #define SWAP_RA_WIN(v)          (((v) & SWAP_RA_WIN_MASK) >> SWAP_RA_WIN_SHIFT)
  49 #define SWAP_RA_ADDR(v)         ((v) & PAGE_MASK)
  50
  51 #define SWAP_RA_VAL(addr, win, hits)                            \
  52         (((addr) & PAGE_MASK) |                                 \
  53          (((win) << SWAP_RA_WIN_SHIFT) & SWAP_RA_WIN_MASK) |    \
  54          ((hits) & SWAP_RA_HITS_MASK))
  55
  56 /* Initial readahead hits is 4 to start up with a small window */
  57 #define GET_SWAP_RA_VAL(vma)                                    \
  58         (atomic_long_read(&(vma)->swap_readahead_info) ? : 4)
  59
  60 #define INC_CACHE_INFO(x)       do { swap_cache_info.x++; } while (0)
  61 #define ADD_CACHE_INFO(x, nr)   do { swap_cache_info.x += (nr); } while (0)
  62
  63 static struct {
  64         unsigned long add_total;
  65         unsigned long del_total;
  66         unsigned long find_success;
  67         unsigned long find_total;
  68 } swap_cache_info;
  69
  70 unsigned long total_swapcache_pages(void)
  71 {
  72         unsigned int i, j, nr;
  73         unsigned long ret = 0;
  74         struct address_space *spaces;
  75
  76         rcu_read_lock();
  77         for (i = 0; i < MAX_SWAPFILES; i++) {
  78                 /*
  79                  * The corresponding entries in nr_swapper_spaces and
  80                  * swapper_spaces will be reused only after at least
  81                  * one grace period.  So it is impossible for them
  82                  * belongs to different usage.
  83                  */
  84                 nr = nr_swapper_spaces[i];
  85                 spaces = rcu_dereference(swapper_spaces[i]);
  86                 if (!nr || !spaces)
  87                         continue;
  88                 for (j = 0; j < nr; j++)
  89                         ret += spaces[j].nrpages;
  90         }
  91         rcu_read_unlock();
  92         return ret;
  93 }
  94
  95 static atomic_t swapin_readahead_hits = ATOMIC_INIT(4);
  96
  97 void show_swap_cache_info(void)
  98 {
  99         printk("%lu pages in swap cache\n", total_swapcache_pages());
 100         printk("Swap cache stats: add %lu, delete %lu, find %lu/%lu\n",
 101                 swap_cache_info.add_total, swap_cache_info.del_total,
 102                 swap_cache_info.find_success, swap_cache_info.find_total);
 103         printk("Free swap  = %ldkB\n",
 104                 get_nr_swap_pages() << (PAGE_SHIFT - 10));
 105         printk("Total swap = %lukB\n", total_swap_pages << (PAGE_SHIFT - 10));
 106 }
 107
 108 /*
 109  * __add_to_swap_cache resembles add_to_page_cache_locked on swapper_space,
 110  * but sets SwapCache flag and private instead of mapping and index.
 111  */
 112 int __add_to_swap_cache(struct page *page, swp_entry_t entry)
 113 {
 114         int error, i, nr = hpage_nr_pages(page);
 115         struct address_space *address_space;
 116         pgoff_t idx = swp_offset(entry);
 117
 118         VM_BUG_ON_PAGE(!PageLocked(page), page);
 119         VM_BUG_ON_PAGE(PageSwapCache(page), page);
 120         VM_BUG_ON_PAGE(!PageSwapBacked(page), page);
 121
 122         page_ref_add(page, nr);
 123         SetPageSwapCache(page);
 124
 125         address_space = swap_address_space(entry);
 126         spin_lock_irq(&address_space->tree_lock);
 127         for (i = 0; i < nr; i++) {
 128                 set_page_private(page + i, entry.val + i);
 129                 error = radix_tree_insert(&address_space->page_tree,
 130                                           idx + i, page + i);
 131                 if (unlikely(error))
 132                         break;
 133         }
 134         if (likely(!error)) {
 135                 address_space->nrpages += nr;
 136                 __mod_node_page_state(page_pgdat(page), NR_FILE_PAGES, nr);
 137                 ADD_CACHE_INFO(add_total, nr);
 138         } else {
 139                 /*
 140                  * Only the context which have set SWAP_HAS_CACHE flag
 141                  * would call add_to_swap_cache().
 142                  * So add_to_swap_cache() doesn't returns -EEXIST.
 143                  */
 144                 VM_BUG_ON(error == -EEXIST);
 145                 set_page_private(page + i, 0UL);
 146                 while (i--) {
 147                         radix_tree_delete(&address_space->page_tree, idx + i);
 148                         set_page_private(page + i, 0UL);
 149                 }
 150                 ClearPageSwapCache(page);
 151                 page_ref_sub(page, nr);
 152         }
 153         spin_unlock_irq(&address_space->tree_lock);
 154
 155         return error;
 156 }
 157
 158
 159 int add_to_swap_cache(struct page *page, swp_entry_t entry, gfp_t gfp_mask)
 160 {
 161         int error;
 162
 163         error = radix_tree_maybe_preload_order(gfp_mask, compound_order(page));
 164         if (!error) {
 165                 error = __add_to_swap_cache(page, entry);
 166                 radix_tree_preload_end();
 167         }
 168         return error;
 169 }
 170
 171 /*
 172  * This must be called only on pages that have
 173  * been verified to be in the swap cache.
 174  */
 175 void __delete_from_swap_cache(struct page *page)
 176 {
 177         struct address_space *address_space;
 178         int i, nr = hpage_nr_pages(page);
 179         swp_entry_t entry;
 180         pgoff_t idx;
 181
 182         VM_BUG_ON_PAGE(!PageLocked(page), page);
 183         VM_BUG_ON_PAGE(!PageSwapCache(page), page);
 184         VM_BUG_ON_PAGE(PageWriteback(page), page);
 185
 186         entry.val = page_private(page);
 187         address_space = swap_address_space(entry);
 188         idx = swp_offset(entry);
 189         for (i = 0; i < nr; i++) {
 190                 radix_tree_delete(&address_space->page_tree, idx + i);
 191                 set_page_private(page + i, 0);
 192         }
 193         ClearPageSwapCache(page);
 194         address_space->nrpages -= nr;
 195         __mod_node_page_state(page_pgdat(page), NR_FILE_PAGES, -nr);
 196         ADD_CACHE_INFO(del_total, nr);
 197 }
 198
 199 /**
 200  * add_to_swap - allocate swap space for a page
 201  * @page: page we want to move to swap
 202  *
 203  * Allocate swap space for the page and add the page to the
 204  * swap cache.  Caller needs to hold the page lock.
 205  */
 206 int add_to_swap(struct page *page)
 207 {
 208         swp_entry_t entry;
 209         int err;
 210
 211         VM_BUG_ON_PAGE(!PageLocked(page), page);
 212         VM_BUG_ON_PAGE(!PageUptodate(page), page);
 213
 214         entry = get_swap_page(page);
 215         if (!entry.val)
 216                 return 0;
 217
 218         if (mem_cgroup_try_charge_swap(page, entry))
 219                 goto fail;
 220
 221         /*
 222          * Radix-tree node allocations from PF_MEMALLOC contexts could
 223          * completely exhaust the page allocator. __GFP_NOMEMALLOC
 224          * stops emergency reserves from being allocated.
 225          *
 226          * TODO: this could cause a theoretical memory reclaim
 227          * deadlock in the swap out path.
 228          */
 229         /*
 230          * Add it to the swap cache.
 231          */
 232         err = add_to_swap_cache(page, entry,
 233                         __GFP_HIGH|__GFP_NOMEMALLOC|__GFP_NOWARN);
 234         /* -ENOMEM radix-tree allocation failure */
 235         if (err)
 236                 /*
 237                  * add_to_swap_cache() doesn't return -EEXIST, so we can safely
 238                  * clear SWAP_HAS_CACHE flag.
 239                  */
 240                 goto fail;
 241         /*
 242          * Normally the page will be dirtied in unmap because its pte should be
 243          * dirty. A special case is MADV_FREE page. The page'e pte could have
 244          * dirty bit cleared but the page's SwapBacked bit is still set because
 245          * clearing the dirty bit and SwapBacked bit has no lock protected. For
 246          * such page, unmap will not set dirty bit for it, so page reclaim will
 247          * not write the page out. This can cause data corruption when the page
 248          * is swap in later. Always setting the dirty bit for the page solves
 249          * the problem.
 250          */
 251         set_page_dirty(page);
 252
 253         return 1;
 254
 255 fail:
 256         put_swap_page(page, entry);
 257         return 0;
 258 }
 259
 260 /*
 261  * This must be called only on pages that have
 262  * been verified to be in the swap cache and locked.
 263  * It will never put the page into the free list,
 264  * the caller has a reference on the page.
 265  */
 266 void delete_from_swap_cache(struct page *page)
 267 {
 268         swp_entry_t entry;
 269         struct address_space *address_space;
 270
 271         entry.val = page_private(page);
 272
 273         address_space = swap_address_space(entry);
 274         spin_lock_irq(&address_space->tree_lock);
 275         __delete_from_swap_cache(page);
 276         spin_unlock_irq(&address_space->tree_lock);
 277
 278         put_swap_page(page, entry);
 279         page_ref_sub(page, hpage_nr_pages(page));
 280 }
 281
 282 /*
 283  * If we are the only user, then try to free up the swap cache.
 284  *
 285  * Its ok to check for PageSwapCache without the page lock
 286  * here because we are going to recheck again inside
 287  * try_to_free_swap() _with_ the lock.
 288  *                                      - Marcelo
 289  */
 290 static inline void free_swap_cache(struct page *page)
 291 {
 292         if (PageSwapCache(page) && !page_mapped(page) && trylock_page(page)) {
 293                 try_to_free_swap(page);
 294                 unlock_page(page);
 295         }
 296 }
 297
 298 /*
 299  * Perform a free_page(), also freeing any swap cache associated with
 300  * this page if it is the last user of the page.
 301  */
 302 void free_page_and_swap_cache(struct page *page)
 303 {
 304         free_swap_cache(page);
 305         if (!is_huge_zero_page(page))
 306                 put_page(page);
 307 }
 308
 309 /*
 310  * Passed an array of pages, drop them all from swapcache and then release
 311  * them.  They are removed from the LRU and freed if this is their last use.
 312  */
 313 void free_pages_and_swap_cache(struct page **pages, int nr)
 314 {
 315         struct page **pagep = pages;
 316         int i;
 317
 318         lru_add_drain();
 319         for (i = 0; i < nr; i++)
 320                 free_swap_cache(pagep[i]);
 321         release_pages(pagep, nr, false);
 322 }
 323
 324 /*
 325  * Lookup a swap entry in the swap cache. A found page will be returned
 326  * unlocked and with its refcount incremented - we rely on the kernel
 327  * lock getting page table operations atomic even if we drop the page
 328  * lock before returning.
 329  */
 330 struct page *lookup_swap_cache(swp_entry_t entry, struct vm_area_struct *vma,
 331                                unsigned long addr)
 332 {
 333         struct page *page;
 334         unsigned long ra_info;
 335         int win, hits, readahead;
 336
 337         page = find_get_page(swap_address_space(entry), swp_offset(entry));
 338
 339         INC_CACHE_INFO(find_total);
 340         if (page) {
 341                 INC_CACHE_INFO(find_success);
 342                 if (unlikely(PageTransCompound(page)))
 343                         return page;
 344                 readahead = TestClearPageReadahead(page);
 345                 if (vma) {
 346                         ra_info = GET_SWAP_RA_VAL(vma);
 347                         win = SWAP_RA_WIN(ra_info);
 348                         hits = SWAP_RA_HITS(ra_info);
 349                         if (readahead)
 350                                 hits = min_t(int, hits + 1, SWAP_RA_HITS_MAX);
 351                         atomic_long_set(&vma->swap_readahead_info,
 352                                         SWAP_RA_VAL(addr, win, hits));
 353                 }
 354                 if (readahead) {
 355                         count_vm_event(SWAP_RA_HIT);
 356                         if (!vma)
 357                                 atomic_inc(&swapin_readahead_hits);
 358                 }
 359         }
 360         return page;
 361 }
 362
 363 struct page *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
 364                         struct vm_area_struct *vma, unsigned long addr,
 365                         bool *new_page_allocated)
 366 {
 367         struct page *found_page, *new_page = NULL;
 368         struct address_space *swapper_space = swap_address_space(entry);
 369         int err;
 370         *new_page_allocated = false;
 371
 372         do {
 373                 /*
 374                  * First check the swap cache.  Since this is normally
 375                  * called after lookup_swap_cache() failed, re-calling
 376                  * that would confuse statistics.
 377                  */
 378                 found_page = find_get_page(swapper_space, swp_offset(entry));
 379                 if (found_page)
 380                         break;
 381
 382                 /*
 383                  * Just skip read ahead for unused swap slot.
 384                  * During swap_off when swap_slot_cache is disabled,
 385                  * we have to handle the race between putting
 386                  * swap entry in swap cache and marking swap slot
 387                  * as SWAP_HAS_CACHE.  That's done in later part of code or
 388                  * else swap_off will be aborted if we return NULL.
 389                  */
 390                 if (!__swp_swapcount(entry) && swap_slot_cache_enabled)
 391                         break;
 392
 393                 /*
 394                  * Get a new page to read into from swap.
 395                  */
 396                 if (!new_page) {
 397                         new_page = alloc_page_vma(gfp_mask, vma, addr);
 398                         if (!new_page)
 399                                 break;          /* Out of memory */
 400                 }
 401
 402                 /*
 403                  * call radix_tree_preload() while we can wait.
 404                  */
 405                 err = radix_tree_maybe_preload(gfp_mask & GFP_KERNEL);
 406                 if (err)
 407                         break;
 408
 409                 /*
 410                  * Swap entry may have been freed since our caller observed it.
 411                  */
 412                 err = swapcache_prepare(entry);
 413                 if (err == -EEXIST) {
 414                         radix_tree_preload_end();
 415                         /*
 416                          * We might race against get_swap_page() and stumble
 417                          * across a SWAP_HAS_CACHE swap_map entry whose page
 418                          * has not been brought into the swapcache yet.
 419                          */
 420                         cond_resched();
 421                         continue;
 422                 }
 423                 if (err) {              /* swp entry is obsolete ? */
 424                         radix_tree_preload_end();
 425                         break;
 426                 }
 427
 428                 /* May fail (-ENOMEM) if radix-tree node allocation failed. */
 429                 __SetPageLocked(new_page);
 430                 __SetPageSwapBacked(new_page);
 431                 err = __add_to_swap_cache(new_page, entry);
 432                 if (likely(!err)) {
 433                         radix_tree_preload_end();
 434                         /*
 435                          * Initiate read into locked page and return.
 436                          */
 437                         lru_cache_add_anon(new_page);
 438                         *new_page_allocated = true;
 439                         return new_page;
 440                 }
 441                 radix_tree_preload_end();
 442                 __ClearPageLocked(new_page);
 443                 /*
 444                  * add_to_swap_cache() doesn't return -EEXIST, so we can safely
 445                  * clear SWAP_HAS_CACHE flag.
 446                  */
 447                 put_swap_page(new_page, entry);
 448         } while (err != -ENOMEM);
 449
 450         if (new_page)
 451                 put_page(new_page);
 452         return found_page;
 453 }
 454
 455 /*
 456  * Locate a page of swap in physical memory, reserving swap cache space
 457  * and reading the disk if it is not already cached.
 458  * A failure return means that either the page allocation failed or that
 459  * the swap entry is no longer in use.
 460  */
 461 struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
 462                 struct vm_area_struct *vma, unsigned long addr, bool do_poll)
 463 {
 464         bool page_was_allocated;
 465         struct page *retpage = __read_swap_cache_async(entry, gfp_mask,
 466                         vma, addr, &page_was_allocated);
 467
 468         if (page_was_allocated)
 469                 swap_readpage(retpage, do_poll);
 470
 471         return retpage;
 472 }
 473
 474 static unsigned int __swapin_nr_pages(unsigned long prev_offset,
 475                                       unsigned long offset,
 476                                       int hits,
 477                                       int max_pages,
 478                                       int prev_win)
 479 {
 480         unsigned int pages, last_ra;
 481
 482         /*
 483          * This heuristic has been found to work well on both sequential and
 484          * random loads, swapping to hard disk or to SSD: please don't ask
 485          * what the "+ 2" means, it just happens to work well, that's all.
 486          */
 487         pages = hits + 2;
 488         if (pages == 2) {
 489                 /*
 490                  * We can have no readahead hits to judge by: but must not get
 491                  * stuck here forever, so check for an adjacent offset instead
 492                  * (and don't even bother to check whether swap type is same).
 493                  */
 494                 if (offset != prev_offset + 1 && offset != prev_offset - 1)
 495                         pages = 1;
 496         } else {
 497                 unsigned int roundup = 4;
 498                 while (roundup < pages)
 499                         roundup <<= 1;
 500                 pages = roundup;
 501         }
 502
 503         if (pages > max_pages)
 504                 pages = max_pages;
 505
 506         /* Don't shrink readahead too fast */
 507         last_ra = prev_win / 2;
 508         if (pages < last_ra)
 509                 pages = last_ra;
 510
 511         return pages;
 512 }
 513
 514 static unsigned long swapin_nr_pages(unsigned long offset)
 515 {
 516         static unsigned long prev_offset;
 517         unsigned int hits, pages, max_pages;
 518         static atomic_t last_readahead_pages;
 519
 520         max_pages = 1 << READ_ONCE(page_cluster);
 521         if (max_pages <= 1)
 522                 return 1;
 523
 524         hits = atomic_xchg(&swapin_readahead_hits, 0);
 525         pages = __swapin_nr_pages(prev_offset, offset, hits, max_pages,
 526                                   atomic_read(&last_readahead_pages));
 527         if (!hits)
 528                 prev_offset = offset;
 529         atomic_set(&last_readahead_pages, pages);
 530
 531         return pages;
 532 }
 533
 534 /**
 535  * swapin_readahead - swap in pages in hope we need them soon
 536  * @entry: swap entry of this memory
 537  * @gfp_mask: memory allocation flags
 538  * @vma: user vma this address belongs to
 539  * @addr: target address for mempolicy
 540  *
 541  * Returns the struct page for entry and addr, after queueing swapin.
 542  *
 543  * Primitive swap readahead code. We simply read an aligned block of
 544  * (1 << page_cluster) entries in the swap area. This method is chosen
 545  * because it doesn't cost us any seek time.  We also make sure to queue
 546  * the 'original' request together with the readahead ones...
 547  *
 548  * This has been extended to use the NUMA policies from the mm triggering
 549  * the readahead.
 550  *
 551  * Caller must hold down_read on the vma->vm_mm if vma is not NULL.
 552  */
 553 struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
 554                         struct vm_area_struct *vma, unsigned long addr)
 555 {
 556         struct page *page;
 557         unsigned long entry_offset = swp_offset(entry);
 558         unsigned long offset = entry_offset;
 559         unsigned long start_offset, end_offset;
 560         unsigned long mask;
 561         struct blk_plug plug;
 562         bool do_poll = true, page_allocated;
 563
 564         mask = swapin_nr_pages(offset) - 1;
 565         if (!mask)
 566                 goto skip;
 567
 568         do_poll = false;
 569         /* Read a page_cluster sized and aligned cluster around offset. */
 570         start_offset = offset & ~mask;
 571         end_offset = offset | mask;
 572         if (!start_offset)      /* First page is swap header. */
 573                 start_offset++;
 574
 575         blk_start_plug(&plug);
 576         for (offset = start_offset; offset <= end_offset ; offset++) {
 577                 /* Ok, do the async read-ahead now */
 578                 page = __read_swap_cache_async(
 579                         swp_entry(swp_type(entry), offset),
 580                         gfp_mask, vma, addr, &page_allocated);
 581                 if (!page)
 582                         continue;
 583                 if (page_allocated) {
 584                         swap_readpage(page, false);
 585                         if (offset != entry_offset &&
 586                             likely(!PageTransCompound(page))) {
 587                                 SetPageReadahead(page);
 588                                 count_vm_event(SWAP_RA);
 589                         }
 590                 }
 591                 put_page(page);
 592         }
 593         blk_finish_plug(&plug);
 594
 595         lru_add_drain();        /* Push any new pages onto the LRU now */
 596 skip:
 597         return read_swap_cache_async(entry, gfp_mask, vma, addr, do_poll);
 598 }
 599
 600 int init_swap_address_space(unsigned int type, unsigned long nr_pages)
 601 {
 602         struct address_space *spaces, *space;
 603         unsigned int i, nr;
 604
 605         nr = DIV_ROUND_UP(nr_pages, SWAP_ADDRESS_SPACE_PAGES);
 606         spaces = kvzalloc(sizeof(struct address_space) * nr, GFP_KERNEL);
 607         if (!spaces)
 608                 return -ENOMEM;
 609         for (i = 0; i < nr; i++) {
 610                 space = spaces + i;
 611                 INIT_RADIX_TREE(&space->page_tree, GFP_ATOMIC|__GFP_NOWARN);
 612                 atomic_set(&space->i_mmap_writable, 0);
 613                 space->a_ops = &swap_aops;
 614                 /* swap cache doesn't use writeback related tags */
 615                 mapping_set_no_writeback_tags(space);
 616                 spin_lock_init(&space->tree_lock);
 617         }
 618         nr_swapper_spaces[type] = nr;
 619         rcu_assign_pointer(swapper_spaces[type], spaces);
 620
 621         return 0;
 622 }
 623
 624 void exit_swap_address_space(unsigned int type)
 625 {
 626         struct address_space *spaces;
 627
 628         spaces = swapper_spaces[type];
 629         nr_swapper_spaces[type] = 0;
 630         rcu_assign_pointer(swapper_spaces[type], NULL);
 631         synchronize_rcu();
 632         kvfree(spaces);
 633 }
 634
 635 static inline void swap_ra_clamp_pfn(struct vm_area_struct *vma,
 636                                      unsigned long faddr,
 637                                      unsigned long lpfn,
 638                                      unsigned long rpfn,
 639                                      unsigned long *start,
 640                                      unsigned long *end)
 641 {
 642         *start = max3(lpfn, PFN_DOWN(vma->vm_start),
 643                       PFN_DOWN(faddr & PMD_MASK));
 644         *end = min3(rpfn, PFN_DOWN(vma->vm_end),
 645                     PFN_DOWN((faddr & PMD_MASK) + PMD_SIZE));
 646 }
 647
 648 struct page *swap_readahead_detect(struct vm_fault *vmf,
 649                                    struct vma_swap_readahead *swap_ra)
 650 {
 651         struct vm_area_struct *vma = vmf->vma;
 652         unsigned long swap_ra_info;
 653         struct page *page;
 654         swp_entry_t entry;
 655         unsigned long faddr, pfn, fpfn;
 656         unsigned long start, end;
 657         pte_t *pte;
 658         unsigned int max_win, hits, prev_win, win, left;
 659 #ifndef CONFIG_64BIT
 660         pte_t *tpte;
 661 #endif
 662
 663         max_win = 1 << min_t(unsigned int, READ_ONCE(page_cluster),
 664                              SWAP_RA_ORDER_CEILING);
 665         if (max_win == 1) {
 666                 swap_ra->win = 1;
 667                 return NULL;
 668         }
 669
 670         faddr = vmf->address;
 671         entry = pte_to_swp_entry(vmf->orig_pte);
 672         if ((unlikely(non_swap_entry(entry))))
 673                 return NULL;
 674         page = lookup_swap_cache(entry, vma, faddr);
 675         if (page)
 676                 return page;
 677
 678         fpfn = PFN_DOWN(faddr);
 679         swap_ra_info = GET_SWAP_RA_VAL(vma);
 680         pfn = PFN_DOWN(SWAP_RA_ADDR(swap_ra_info));
 681         prev_win = SWAP_RA_WIN(swap_ra_info);
 682         hits = SWAP_RA_HITS(swap_ra_info);
 683         swap_ra->win = win = __swapin_nr_pages(pfn, fpfn, hits,
 684                                                max_win, prev_win);
 685         atomic_long_set(&vma->swap_readahead_info,
 686                         SWAP_RA_VAL(faddr, win, 0));
 687
 688         if (win == 1)
 689                 return NULL;
 690
 691         /* Copy the PTEs because the page table may be unmapped */
 692         if (fpfn == pfn + 1)
 693                 swap_ra_clamp_pfn(vma, faddr, fpfn, fpfn + win, &start, &end);
 694         else if (pfn == fpfn + 1)
 695                 swap_ra_clamp_pfn(vma, faddr, fpfn - win + 1, fpfn + 1,
 696                                   &start, &end);
 697         else {
 698                 left = (win - 1) / 2;
 699                 swap_ra_clamp_pfn(vma, faddr, fpfn - left, fpfn + win - left,
 700                                   &start, &end);
 701         }
 702         swap_ra->nr_pte = end - start;
 703         swap_ra->offset = fpfn - start;
 704         pte = vmf->pte - swap_ra->offset;
 705 #ifdef CONFIG_64BIT
 706         swap_ra->ptes = pte;
 707 #else
 708         tpte = swap_ra->ptes;
 709         for (pfn = start; pfn != end; pfn++)
 710                 *tpte++ = *pte++;
 711 #endif
 712
 713         return NULL;
 714 }
 715
 716 struct page *do_swap_page_readahead(swp_entry_t fentry, gfp_t gfp_mask,
 717                                     struct vm_fault *vmf,
 718                                     struct vma_swap_readahead *swap_ra)
 719 {
 720         struct blk_plug plug;
 721         struct vm_area_struct *vma = vmf->vma;
 722         struct page *page;
 723         pte_t *pte, pentry;
 724         swp_entry_t entry;
 725         unsigned int i;
 726         bool page_allocated;
 727
 728         if (swap_ra->win == 1)
 729                 goto skip;
 730
 731         blk_start_plug(&plug);
 732         for (i = 0, pte = swap_ra->ptes; i < swap_ra->nr_pte;
 733              i++, pte++) {
 734                 pentry = *pte;
 735                 if (pte_none(pentry))
 736                         continue;
 737                 if (pte_present(pentry))
 738                         continue;
 739                 entry = pte_to_swp_entry(pentry);
 740                 if (unlikely(non_swap_entry(entry)))
 741                         continue;
 742                 page = __read_swap_cache_async(entry, gfp_mask, vma,
 743                                                vmf->address, &page_allocated);
 744                 if (!page)
 745                         continue;
 746                 if (page_allocated) {
 747                         swap_readpage(page, false);
 748                         if (i != swap_ra->offset &&
 749                             likely(!PageTransCompound(page))) {
 750                                 SetPageReadahead(page);
 751                                 count_vm_event(SWAP_RA);
 752                         }
 753                 }
 754                 put_page(page);
 755         }
 756         blk_finish_plug(&plug);
 757         lru_add_drain();
 758 skip:
 759         return read_swap_cache_async(fentry, gfp_mask, vma, vmf->address,
 760                                      swap_ra->win == 1);
 761 }
 762
 763 #ifdef CONFIG_SYSFS
 764 static ssize_t vma_ra_enabled_show(struct kobject *kobj,
 765                                      struct kobj_attribute *attr, char *buf)
 766 {
 767         return sprintf(buf, "%s\n", swap_vma_readahead ? "true" : "false");
 768 }
 769 static ssize_t vma_ra_enabled_store(struct kobject *kobj,
 770                                       struct kobj_attribute *attr,
 771                                       const char *buf, size_t count)
 772 {
 773         if (!strncmp(buf, "true", 4) || !strncmp(buf, "1", 1))
 774                 swap_vma_readahead = true;
 775         else if (!strncmp(buf, "false", 5) || !strncmp(buf, "0", 1))
 776                 swap_vma_readahead = false;
 777         else
 778                 return -EINVAL;
 779
 780         return count;
 781 }
 782 static struct kobj_attribute vma_ra_enabled_attr =
 783         __ATTR(vma_ra_enabled, 0644, vma_ra_enabled_show,
 784                vma_ra_enabled_store);
 785
 786 static struct attribute *swap_attrs[] = {
 787         &vma_ra_enabled_attr.attr,
 788         NULL,
 789 };
 790
 791 static struct attribute_group swap_attr_group = {
 792         .attrs = swap_attrs,
 793 };
 794
 795 static int __init swap_init_sysfs(void)
 796 {
 797         int err;
 798         struct kobject *swap_kobj;
 799
 800         swap_kobj = kobject_create_and_add("swap", mm_kobj);
 801         if (!swap_kobj) {
 802                 pr_err("failed to create swap kobject\n");
 803                 return -ENOMEM;
 804         }
 805         err = sysfs_create_group(swap_kobj, &swap_attr_group);
 806         if (err) {
 807                 pr_err("failed to register swap group\n");
 808                 goto delete_obj;
 809         }
 810         return 0;
 811
 812 delete_obj:
 813         kobject_put(swap_kobj);
 814         return err;
 815 }
 816 subsys_initcall(swap_init_sysfs);
 817 #endif