mm/swap_state.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  *  linux/mm/swap_state.c
   4  *
   5  *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
   6  *  Swap reorganised 29.12.95, Stephen Tweedie
   7  *
   8  *  Rewritten to use page cache, (C) 1998 Stephen Tweedie
   9  */
  10 #include <linux/mm.h>
  11 #include <linux/gfp.h>
  12 #include <linux/kernel_stat.h>
  13 #include <linux/swap.h>
  14 #include <linux/swapops.h>
  15 #include <linux/init.h>
  16 #include <linux/pagemap.h>
  17 #include <linux/backing-dev.h>
  18 #include <linux/blkdev.h>
  19 #include <linux/pagevec.h>
  20 #include <linux/migrate.h>
  21 #include <linux/vmalloc.h>
  22 #include <linux/swap_slots.h>
  23 #include <linux/huge_mm.h>
  24
  25 #include <asm/pgtable.h>
  26 #include "internal.h"
  27
  28 /*
  29  * swapper_space is a fiction, retained to simplify the path through
  30  * vmscan's shrink_page_list.
  31  */
  32 static const struct address_space_operations swap_aops = {
  33         .writepage      = swap_writepage,
  34         .set_page_dirty = swap_set_page_dirty,
  35 #ifdef CONFIG_MIGRATION
  36         .migratepage    = migrate_page,
  37 #endif
  38 };
  39
  40 struct address_space *swapper_spaces[MAX_SWAPFILES];
  41 static unsigned int nr_swapper_spaces[MAX_SWAPFILES];
  42 bool swap_vma_readahead = true;
  43
  44 #define SWAP_RA_WIN_SHIFT       (PAGE_SHIFT / 2)
  45 #define SWAP_RA_HITS_MASK       ((1UL << SWAP_RA_WIN_SHIFT) - 1)
  46 #define SWAP_RA_HITS_MAX        SWAP_RA_HITS_MASK
  47 #define SWAP_RA_WIN_MASK        (~PAGE_MASK & ~SWAP_RA_HITS_MASK)
  48
  49 #define SWAP_RA_HITS(v)         ((v) & SWAP_RA_HITS_MASK)
  50 #define SWAP_RA_WIN(v)          (((v) & SWAP_RA_WIN_MASK) >> SWAP_RA_WIN_SHIFT)
  51 #define SWAP_RA_ADDR(v)         ((v) & PAGE_MASK)
  52
  53 #define SWAP_RA_VAL(addr, win, hits)                            \
  54         (((addr) & PAGE_MASK) |                                 \
  55          (((win) << SWAP_RA_WIN_SHIFT) & SWAP_RA_WIN_MASK) |    \
  56          ((hits) & SWAP_RA_HITS_MASK))
  57
  58 /* Initial readahead hits is 4 to start up with a small window */
  59 #define GET_SWAP_RA_VAL(vma)                                    \
  60         (atomic_long_read(&(vma)->swap_readahead_info) ? : 4)
  61
  62 #define INC_CACHE_INFO(x)       do { swap_cache_info.x++; } while (0)
  63 #define ADD_CACHE_INFO(x, nr)   do { swap_cache_info.x += (nr); } while (0)
  64
  65 static struct {
  66         unsigned long add_total;
  67         unsigned long del_total;
  68         unsigned long find_success;
  69         unsigned long find_total;
  70 } swap_cache_info;
  71
  72 unsigned long total_swapcache_pages(void)
  73 {
  74         unsigned int i, j, nr;
  75         unsigned long ret = 0;
  76         struct address_space *spaces;
  77
  78         rcu_read_lock();
  79         for (i = 0; i < MAX_SWAPFILES; i++) {
  80                 /*
  81                  * The corresponding entries in nr_swapper_spaces and
  82                  * swapper_spaces will be reused only after at least
  83                  * one grace period.  So it is impossible for them
  84                  * belongs to different usage.
  85                  */
  86                 nr = nr_swapper_spaces[i];
  87                 spaces = rcu_dereference(swapper_spaces[i]);
  88                 if (!nr || !spaces)
  89                         continue;
  90                 for (j = 0; j < nr; j++)
  91                         ret += spaces[j].nrpages;
  92         }
  93         rcu_read_unlock();
  94         return ret;
  95 }
  96
  97 static atomic_t swapin_readahead_hits = ATOMIC_INIT(4);
  98
  99 void show_swap_cache_info(void)
 100 {
 101         printk("%lu pages in swap cache\n", total_swapcache_pages());
 102         printk("Swap cache stats: add %lu, delete %lu, find %lu/%lu\n",
 103                 swap_cache_info.add_total, swap_cache_info.del_total,
 104                 swap_cache_info.find_success, swap_cache_info.find_total);
 105         printk("Free swap  = %ldkB\n",
 106                 get_nr_swap_pages() << (PAGE_SHIFT - 10));
 107         printk("Total swap = %lukB\n", total_swap_pages << (PAGE_SHIFT - 10));
 108 }
 109
 110 /*
 111  * __add_to_swap_cache resembles add_to_page_cache_locked on swapper_space,
 112  * but sets SwapCache flag and private instead of mapping and index.
 113  */
 114 int __add_to_swap_cache(struct page *page, swp_entry_t entry)
 115 {
 116         int error, i, nr = hpage_nr_pages(page);
 117         struct address_space *address_space;
 118         pgoff_t idx = swp_offset(entry);
 119
 120         VM_BUG_ON_PAGE(!PageLocked(page), page);
 121         VM_BUG_ON_PAGE(PageSwapCache(page), page);
 122         VM_BUG_ON_PAGE(!PageSwapBacked(page), page);
 123
 124         page_ref_add(page, nr);
 125         SetPageSwapCache(page);
 126
 127         address_space = swap_address_space(entry);
 128         spin_lock_irq(&address_space->tree_lock);
 129         for (i = 0; i < nr; i++) {
 130                 set_page_private(page + i, entry.val + i);
 131                 error = radix_tree_insert(&address_space->page_tree,
 132                                           idx + i, page + i);
 133                 if (unlikely(error))
 134                         break;
 135         }
 136         if (likely(!error)) {
 137                 address_space->nrpages += nr;
 138                 __mod_node_page_state(page_pgdat(page), NR_FILE_PAGES, nr);
 139                 ADD_CACHE_INFO(add_total, nr);
 140         } else {
 141                 /*
 142                  * Only the context which have set SWAP_HAS_CACHE flag
 143                  * would call add_to_swap_cache().
 144                  * So add_to_swap_cache() doesn't returns -EEXIST.
 145                  */
 146                 VM_BUG_ON(error == -EEXIST);
 147                 set_page_private(page + i, 0UL);
 148                 while (i--) {
 149                         radix_tree_delete(&address_space->page_tree, idx + i);
 150                         set_page_private(page + i, 0UL);
 151                 }
 152                 ClearPageSwapCache(page);
 153                 page_ref_sub(page, nr);
 154         }
 155         spin_unlock_irq(&address_space->tree_lock);
 156
 157         return error;
 158 }
 159
 160
 161 int add_to_swap_cache(struct page *page, swp_entry_t entry, gfp_t gfp_mask)
 162 {
 163         int error;
 164
 165         error = radix_tree_maybe_preload_order(gfp_mask, compound_order(page));
 166         if (!error) {
 167                 error = __add_to_swap_cache(page, entry);
 168                 radix_tree_preload_end();
 169         }
 170         return error;
 171 }
 172
 173 /*
 174  * This must be called only on pages that have
 175  * been verified to be in the swap cache.
 176  */
 177 void __delete_from_swap_cache(struct page *page)
 178 {
 179         struct address_space *address_space;
 180         int i, nr = hpage_nr_pages(page);
 181         swp_entry_t entry;
 182         pgoff_t idx;
 183
 184         VM_BUG_ON_PAGE(!PageLocked(page), page);
 185         VM_BUG_ON_PAGE(!PageSwapCache(page), page);
 186         VM_BUG_ON_PAGE(PageWriteback(page), page);
 187
 188         entry.val = page_private(page);
 189         address_space = swap_address_space(entry);
 190         idx = swp_offset(entry);
 191         for (i = 0; i < nr; i++) {
 192                 radix_tree_delete(&address_space->page_tree, idx + i);
 193                 set_page_private(page + i, 0);
 194         }
 195         ClearPageSwapCache(page);
 196         address_space->nrpages -= nr;
 197         __mod_node_page_state(page_pgdat(page), NR_FILE_PAGES, -nr);
 198         ADD_CACHE_INFO(del_total, nr);
 199 }
 200
 201 /**
 202  * add_to_swap - allocate swap space for a page
 203  * @page: page we want to move to swap
 204  *
 205  * Allocate swap space for the page and add the page to the
 206  * swap cache.  Caller needs to hold the page lock.
 207  */
 208 int add_to_swap(struct page *page)
 209 {
 210         swp_entry_t entry;
 211         int err;
 212
 213         VM_BUG_ON_PAGE(!PageLocked(page), page);
 214         VM_BUG_ON_PAGE(!PageUptodate(page), page);
 215
 216         entry = get_swap_page(page);
 217         if (!entry.val)
 218                 return 0;
 219
 220         if (mem_cgroup_try_charge_swap(page, entry))
 221                 goto fail;
 222
 223         /*
 224          * Radix-tree node allocations from PF_MEMALLOC contexts could
 225          * completely exhaust the page allocator. __GFP_NOMEMALLOC
 226          * stops emergency reserves from being allocated.
 227          *
 228          * TODO: this could cause a theoretical memory reclaim
 229          * deadlock in the swap out path.
 230          */
 231         /*
 232          * Add it to the swap cache.
 233          */
 234         err = add_to_swap_cache(page, entry,
 235                         __GFP_HIGH|__GFP_NOMEMALLOC|__GFP_NOWARN);
 236         /* -ENOMEM radix-tree allocation failure */
 237         if (err)
 238                 /*
 239                  * add_to_swap_cache() doesn't return -EEXIST, so we can safely
 240                  * clear SWAP_HAS_CACHE flag.
 241                  */
 242                 goto fail;
 243         /*
 244          * Normally the page will be dirtied in unmap because its pte should be
 245          * dirty. A special case is MADV_FREE page. The page'e pte could have
 246          * dirty bit cleared but the page's SwapBacked bit is still set because
 247          * clearing the dirty bit and SwapBacked bit has no lock protected. For
 248          * such page, unmap will not set dirty bit for it, so page reclaim will
 249          * not write the page out. This can cause data corruption when the page
 250          * is swap in later. Always setting the dirty bit for the page solves
 251          * the problem.
 252          */
 253         set_page_dirty(page);
 254
 255         return 1;
 256
 257 fail:
 258         put_swap_page(page, entry);
 259         return 0;
 260 }
 261
 262 /*
 263  * This must be called only on pages that have
 264  * been verified to be in the swap cache and locked.
 265  * It will never put the page into the free list,
 266  * the caller has a reference on the page.
 267  */
 268 void delete_from_swap_cache(struct page *page)
 269 {
 270         swp_entry_t entry;
 271         struct address_space *address_space;
 272
 273         entry.val = page_private(page);
 274
 275         address_space = swap_address_space(entry);
 276         spin_lock_irq(&address_space->tree_lock);
 277         __delete_from_swap_cache(page);
 278         spin_unlock_irq(&address_space->tree_lock);
 279
 280         put_swap_page(page, entry);
 281         page_ref_sub(page, hpage_nr_pages(page));
 282 }
 283
 284 /*
 285  * If we are the only user, then try to free up the swap cache.
 286  *
 287  * Its ok to check for PageSwapCache without the page lock
 288  * here because we are going to recheck again inside
 289  * try_to_free_swap() _with_ the lock.
 290  *                                      - Marcelo
 291  */
 292 static inline void free_swap_cache(struct page *page)
 293 {
 294         if (PageSwapCache(page) && !page_mapped(page) && trylock_page(page)) {
 295                 try_to_free_swap(page);
 296                 unlock_page(page);
 297         }
 298 }
 299
 300 /*
 301  * Perform a free_page(), also freeing any swap cache associated with
 302  * this page if it is the last user of the page.
 303  */
 304 void free_page_and_swap_cache(struct page *page)
 305 {
 306         free_swap_cache(page);
 307         if (!is_huge_zero_page(page))
 308                 put_page(page);
 309 }
 310
 311 /*
 312  * Passed an array of pages, drop them all from swapcache and then release
 313  * them.  They are removed from the LRU and freed if this is their last use.
 314  */
 315 void free_pages_and_swap_cache(struct page **pages, int nr)
 316 {
 317         struct page **pagep = pages;
 318         int i;
 319
 320         lru_add_drain();
 321         for (i = 0; i < nr; i++)
 322                 free_swap_cache(pagep[i]);
 323         release_pages(pagep, nr, false);
 324 }
 325
 326 /*
 327  * Lookup a swap entry in the swap cache. A found page will be returned
 328  * unlocked and with its refcount incremented - we rely on the kernel
 329  * lock getting page table operations atomic even if we drop the page
 330  * lock before returning.
 331  */
 332 struct page *lookup_swap_cache(swp_entry_t entry, struct vm_area_struct *vma,
 333                                unsigned long addr)
 334 {
 335         struct page *page;
 336         unsigned long ra_info;
 337         int win, hits, readahead;
 338
 339         page = find_get_page(swap_address_space(entry), swp_offset(entry));
 340
 341         INC_CACHE_INFO(find_total);
 342         if (page) {
 343                 INC_CACHE_INFO(find_success);
 344                 if (unlikely(PageTransCompound(page)))
 345                         return page;
 346                 readahead = TestClearPageReadahead(page);
 347                 if (vma) {
 348                         ra_info = GET_SWAP_RA_VAL(vma);
 349                         win = SWAP_RA_WIN(ra_info);
 350                         hits = SWAP_RA_HITS(ra_info);
 351                         if (readahead)
 352                                 hits = min_t(int, hits + 1, SWAP_RA_HITS_MAX);
 353                         atomic_long_set(&vma->swap_readahead_info,
 354                                         SWAP_RA_VAL(addr, win, hits));
 355                 }
 356                 if (readahead) {
 357                         count_vm_event(SWAP_RA_HIT);
 358                         if (!vma)
 359                                 atomic_inc(&swapin_readahead_hits);
 360                 }
 361         }
 362         return page;
 363 }
 364
 365 struct page *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
 366                         struct vm_area_struct *vma, unsigned long addr,
 367                         bool *new_page_allocated)
 368 {
 369         struct page *found_page, *new_page = NULL;
 370         struct address_space *swapper_space = swap_address_space(entry);
 371         int err;
 372         *new_page_allocated = false;
 373
 374         do {
 375                 /*
 376                  * First check the swap cache.  Since this is normally
 377                  * called after lookup_swap_cache() failed, re-calling
 378                  * that would confuse statistics.
 379                  */
 380                 found_page = find_get_page(swapper_space, swp_offset(entry));
 381                 if (found_page)
 382                         break;
 383
 384                 /*
 385                  * Just skip read ahead for unused swap slot.
 386                  * During swap_off when swap_slot_cache is disabled,
 387                  * we have to handle the race between putting
 388                  * swap entry in swap cache and marking swap slot
 389                  * as SWAP_HAS_CACHE.  That's done in later part of code or
 390                  * else swap_off will be aborted if we return NULL.
 391                  */
 392                 if (!__swp_swapcount(entry) && swap_slot_cache_enabled)
 393                         break;
 394
 395                 /*
 396                  * Get a new page to read into from swap.
 397                  */
 398                 if (!new_page) {
 399                         new_page = alloc_page_vma(gfp_mask, vma, addr);
 400                         if (!new_page)
 401                                 break;          /* Out of memory */
 402                 }
 403
 404                 /*
 405                  * call radix_tree_preload() while we can wait.
 406                  */
 407                 err = radix_tree_maybe_preload(gfp_mask & GFP_RECLAIM_MASK);
 408                 if (err)
 409                         break;
 410
 411                 /*
 412                  * Swap entry may have been freed since our caller observed it.
 413                  */
 414                 err = swapcache_prepare(entry);
 415                 if (err == -EEXIST) {
 416                         radix_tree_preload_end();
 417                         /*
 418                          * We might race against get_swap_page() and stumble
 419                          * across a SWAP_HAS_CACHE swap_map entry whose page
 420                          * has not been brought into the swapcache yet.
 421                          */
 422                         cond_resched();
 423                         continue;
 424                 }
 425                 if (err) {              /* swp entry is obsolete ? */
 426                         radix_tree_preload_end();
 427                         break;
 428                 }
 429
 430                 /* May fail (-ENOMEM) if radix-tree node allocation failed. */
 431                 __SetPageLocked(new_page);
 432                 __SetPageSwapBacked(new_page);
 433                 err = __add_to_swap_cache(new_page, entry);
 434                 if (likely(!err)) {
 435                         radix_tree_preload_end();
 436                         /*
 437                          * Initiate read into locked page and return.
 438                          */
 439                         lru_cache_add_anon(new_page);
 440                         *new_page_allocated = true;
 441                         return new_page;
 442                 }
 443                 radix_tree_preload_end();
 444                 __ClearPageLocked(new_page);
 445                 /*
 446                  * add_to_swap_cache() doesn't return -EEXIST, so we can safely
 447                  * clear SWAP_HAS_CACHE flag.
 448                  */
 449                 put_swap_page(new_page, entry);
 450         } while (err != -ENOMEM);
 451
 452         if (new_page)
 453                 put_page(new_page);
 454         return found_page;
 455 }
 456
 457 /*
 458  * Locate a page of swap in physical memory, reserving swap cache space
 459  * and reading the disk if it is not already cached.
 460  * A failure return means that either the page allocation failed or that
 461  * the swap entry is no longer in use.
 462  */
 463 struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
 464                 struct vm_area_struct *vma, unsigned long addr, bool do_poll)
 465 {
 466         bool page_was_allocated;
 467         struct page *retpage = __read_swap_cache_async(entry, gfp_mask,
 468                         vma, addr, &page_was_allocated);
 469
 470         if (page_was_allocated)
 471                 swap_readpage(retpage, do_poll);
 472
 473         return retpage;
 474 }
 475
 476 static unsigned int __swapin_nr_pages(unsigned long prev_offset,
 477                                       unsigned long offset,
 478                                       int hits,
 479                                       int max_pages,
 480                                       int prev_win)
 481 {
 482         unsigned int pages, last_ra;
 483
 484         /*
 485          * This heuristic has been found to work well on both sequential and
 486          * random loads, swapping to hard disk or to SSD: please don't ask
 487          * what the "+ 2" means, it just happens to work well, that's all.
 488          */
 489         pages = hits + 2;
 490         if (pages == 2) {
 491                 /*
 492                  * We can have no readahead hits to judge by: but must not get
 493                  * stuck here forever, so check for an adjacent offset instead
 494                  * (and don't even bother to check whether swap type is same).
 495                  */
 496                 if (offset != prev_offset + 1 && offset != prev_offset - 1)
 497                         pages = 1;
 498         } else {
 499                 unsigned int roundup = 4;
 500                 while (roundup < pages)
 501                         roundup <<= 1;
 502                 pages = roundup;
 503         }
 504
 505         if (pages > max_pages)
 506                 pages = max_pages;
 507
 508         /* Don't shrink readahead too fast */
 509         last_ra = prev_win / 2;
 510         if (pages < last_ra)
 511                 pages = last_ra;
 512
 513         return pages;
 514 }
 515
 516 static unsigned long swapin_nr_pages(unsigned long offset)
 517 {
 518         static unsigned long prev_offset;
 519         unsigned int hits, pages, max_pages;
 520         static atomic_t last_readahead_pages;
 521
 522         max_pages = 1 << READ_ONCE(page_cluster);
 523         if (max_pages <= 1)
 524                 return 1;
 525
 526         hits = atomic_xchg(&swapin_readahead_hits, 0);
 527         pages = __swapin_nr_pages(READ_ONCE(prev_offset), offset, hits,
 528                                   max_pages,
 529                                   atomic_read(&last_readahead_pages));
 530         if (!hits)
 531                 WRITE_ONCE(prev_offset, offset);
 532         atomic_set(&last_readahead_pages, pages);
 533
 534         return pages;
 535 }
 536
 537 /**
 538  * swapin_readahead - swap in pages in hope we need them soon
 539  * @entry: swap entry of this memory
 540  * @gfp_mask: memory allocation flags
 541  * @vma: user vma this address belongs to
 542  * @addr: target address for mempolicy
 543  *
 544  * Returns the struct page for entry and addr, after queueing swapin.
 545  *
 546  * Primitive swap readahead code. We simply read an aligned block of
 547  * (1 << page_cluster) entries in the swap area. This method is chosen
 548  * because it doesn't cost us any seek time.  We also make sure to queue
 549  * the 'original' request together with the readahead ones...
 550  *
 551  * This has been extended to use the NUMA policies from the mm triggering
 552  * the readahead.
 553  *
 554  * Caller must hold down_read on the vma->vm_mm if vma is not NULL.
 555  */
 556 struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
 557                         struct vm_area_struct *vma, unsigned long addr)
 558 {
 559         struct page *page;
 560         unsigned long entry_offset = swp_offset(entry);
 561         unsigned long offset = entry_offset;
 562         unsigned long start_offset, end_offset;
 563         unsigned long mask;
 564         struct blk_plug plug;
 565         bool do_poll = true, page_allocated;
 566
 567         mask = swapin_nr_pages(offset) - 1;
 568         if (!mask)
 569                 goto skip;
 570
 571         do_poll = false;
 572         /* Read a page_cluster sized and aligned cluster around offset. */
 573         start_offset = offset & ~mask;
 574         end_offset = offset | mask;
 575         if (!start_offset)      /* First page is swap header. */
 576                 start_offset++;
 577
 578         blk_start_plug(&plug);
 579         for (offset = start_offset; offset <= end_offset ; offset++) {
 580                 /* Ok, do the async read-ahead now */
 581                 page = __read_swap_cache_async(
 582                         swp_entry(swp_type(entry), offset),
 583                         gfp_mask, vma, addr, &page_allocated);
 584                 if (!page)
 585                         continue;
 586                 if (page_allocated) {
 587                         swap_readpage(page, false);
 588                         if (offset != entry_offset &&
 589                             likely(!PageTransCompound(page))) {
 590                                 SetPageReadahead(page);
 591                                 count_vm_event(SWAP_RA);
 592                         }
 593                 }
 594                 put_page(page);
 595         }
 596         blk_finish_plug(&plug);
 597
 598         lru_add_drain();        /* Push any new pages onto the LRU now */
 599 skip:
 600         return read_swap_cache_async(entry, gfp_mask, vma, addr, do_poll);
 601 }
 602
 603 int init_swap_address_space(unsigned int type, unsigned long nr_pages)
 604 {
 605         struct address_space *spaces, *space;
 606         unsigned int i, nr;
 607
 608         nr = DIV_ROUND_UP(nr_pages, SWAP_ADDRESS_SPACE_PAGES);
 609         spaces = kvzalloc(sizeof(struct address_space) * nr, GFP_KERNEL);
 610         if (!spaces)
 611                 return -ENOMEM;
 612         for (i = 0; i < nr; i++) {
 613                 space = spaces + i;
 614                 INIT_RADIX_TREE(&space->page_tree, GFP_ATOMIC|__GFP_NOWARN);
 615                 atomic_set(&space->i_mmap_writable, 0);
 616                 space->a_ops = &swap_aops;
 617                 /* swap cache doesn't use writeback related tags */
 618                 mapping_set_no_writeback_tags(space);
 619                 spin_lock_init(&space->tree_lock);
 620         }
 621         nr_swapper_spaces[type] = nr;
 622         rcu_assign_pointer(swapper_spaces[type], spaces);
 623
 624         return 0;
 625 }
 626
 627 void exit_swap_address_space(unsigned int type)
 628 {
 629         struct address_space *spaces;
 630
 631         spaces = swapper_spaces[type];
 632         nr_swapper_spaces[type] = 0;
 633         rcu_assign_pointer(swapper_spaces[type], NULL);
 634         synchronize_rcu();
 635         kvfree(spaces);
 636 }
 637
 638 static inline void swap_ra_clamp_pfn(struct vm_area_struct *vma,
 639                                      unsigned long faddr,
 640                                      unsigned long lpfn,
 641                                      unsigned long rpfn,
 642                                      unsigned long *start,
 643                                      unsigned long *end)
 644 {
 645         *start = max3(lpfn, PFN_DOWN(vma->vm_start),
 646                       PFN_DOWN(faddr & PMD_MASK));
 647         *end = min3(rpfn, PFN_DOWN(vma->vm_end),
 648                     PFN_DOWN((faddr & PMD_MASK) + PMD_SIZE));
 649 }
 650
 651 struct page *swap_readahead_detect(struct vm_fault *vmf,
 652                                    struct vma_swap_readahead *swap_ra)
 653 {
 654         struct vm_area_struct *vma = vmf->vma;
 655         unsigned long swap_ra_info;
 656         struct page *page;
 657         swp_entry_t entry;
 658         unsigned long faddr, pfn, fpfn;
 659         unsigned long start, end;
 660         pte_t *pte;
 661         unsigned int max_win, hits, prev_win, win, left;
 662 #ifndef CONFIG_64BIT
 663         pte_t *tpte;
 664 #endif
 665
 666         max_win = 1 << min_t(unsigned int, READ_ONCE(page_cluster),
 667                              SWAP_RA_ORDER_CEILING);
 668         if (max_win == 1) {
 669                 swap_ra->win = 1;
 670                 return NULL;
 671         }
 672
 673         faddr = vmf->address;
 674         entry = pte_to_swp_entry(vmf->orig_pte);
 675         if ((unlikely(non_swap_entry(entry))))
 676                 return NULL;
 677         page = lookup_swap_cache(entry, vma, faddr);
 678         if (page)
 679                 return page;
 680
 681         fpfn = PFN_DOWN(faddr);
 682         swap_ra_info = GET_SWAP_RA_VAL(vma);
 683         pfn = PFN_DOWN(SWAP_RA_ADDR(swap_ra_info));
 684         prev_win = SWAP_RA_WIN(swap_ra_info);
 685         hits = SWAP_RA_HITS(swap_ra_info);
 686         swap_ra->win = win = __swapin_nr_pages(pfn, fpfn, hits,
 687                                                max_win, prev_win);
 688         atomic_long_set(&vma->swap_readahead_info,
 689                         SWAP_RA_VAL(faddr, win, 0));
 690
 691         if (win == 1)
 692                 return NULL;
 693
 694         /* Copy the PTEs because the page table may be unmapped */
 695         if (fpfn == pfn + 1)
 696                 swap_ra_clamp_pfn(vma, faddr, fpfn, fpfn + win, &start, &end);
 697         else if (pfn == fpfn + 1)
 698                 swap_ra_clamp_pfn(vma, faddr, fpfn - win + 1, fpfn + 1,
 699                                   &start, &end);
 700         else {
 701                 left = (win - 1) / 2;
 702                 swap_ra_clamp_pfn(vma, faddr, fpfn - left, fpfn + win - left,
 703                                   &start, &end);
 704         }
 705         swap_ra->nr_pte = end - start;
 706         swap_ra->offset = fpfn - start;
 707         pte = vmf->pte - swap_ra->offset;
 708 #ifdef CONFIG_64BIT
 709         swap_ra->ptes = pte;
 710 #else
 711         tpte = swap_ra->ptes;
 712         for (pfn = start; pfn != end; pfn++)
 713                 *tpte++ = *pte++;
 714 #endif
 715
 716         return NULL;
 717 }
 718
 719 struct page *do_swap_page_readahead(swp_entry_t fentry, gfp_t gfp_mask,
 720                                     struct vm_fault *vmf,
 721                                     struct vma_swap_readahead *swap_ra)
 722 {
 723         struct blk_plug plug;
 724         struct vm_area_struct *vma = vmf->vma;
 725         struct page *page;
 726         pte_t *pte, pentry;
 727         swp_entry_t entry;
 728         unsigned int i;
 729         bool page_allocated;
 730
 731         if (swap_ra->win == 1)
 732                 goto skip;
 733
 734         blk_start_plug(&plug);
 735         for (i = 0, pte = swap_ra->ptes; i < swap_ra->nr_pte;
 736              i++, pte++) {
 737                 pentry = *pte;
 738                 if (pte_none(pentry))
 739                         continue;
 740                 if (pte_present(pentry))
 741                         continue;
 742                 entry = pte_to_swp_entry(pentry);
 743                 if (unlikely(non_swap_entry(entry)))
 744                         continue;
 745                 page = __read_swap_cache_async(entry, gfp_mask, vma,
 746                                                vmf->address, &page_allocated);
 747                 if (!page)
 748                         continue;
 749                 if (page_allocated) {
 750                         swap_readpage(page, false);
 751                         if (i != swap_ra->offset &&
 752                             likely(!PageTransCompound(page))) {
 753                                 SetPageReadahead(page);
 754                                 count_vm_event(SWAP_RA);
 755                         }
 756                 }
 757                 put_page(page);
 758         }
 759         blk_finish_plug(&plug);
 760         lru_add_drain();
 761 skip:
 762         return read_swap_cache_async(fentry, gfp_mask, vma, vmf->address,
 763                                      swap_ra->win == 1);
 764 }
 765
 766 #ifdef CONFIG_SYSFS
 767 static ssize_t vma_ra_enabled_show(struct kobject *kobj,
 768                                      struct kobj_attribute *attr, char *buf)
 769 {
 770         return sprintf(buf, "%s\n", swap_vma_readahead ? "true" : "false");
 771 }
 772 static ssize_t vma_ra_enabled_store(struct kobject *kobj,
 773                                       struct kobj_attribute *attr,
 774                                       const char *buf, size_t count)
 775 {
 776         if (!strncmp(buf, "true", 4) || !strncmp(buf, "1", 1))
 777                 swap_vma_readahead = true;
 778         else if (!strncmp(buf, "false", 5) || !strncmp(buf, "0", 1))
 779                 swap_vma_readahead = false;
 780         else
 781                 return -EINVAL;
 782
 783         return count;
 784 }
 785 static struct kobj_attribute vma_ra_enabled_attr =
 786         __ATTR(vma_ra_enabled, 0644, vma_ra_enabled_show,
 787                vma_ra_enabled_store);
 788
 789 static struct attribute *swap_attrs[] = {
 790         &vma_ra_enabled_attr.attr,
 791         NULL,
 792 };
 793
 794 static struct attribute_group swap_attr_group = {
 795         .attrs = swap_attrs,
 796 };
 797
 798 static int __init swap_init_sysfs(void)
 799 {
 800         int err;
 801         struct kobject *swap_kobj;
 802
 803         swap_kobj = kobject_create_and_add("swap", mm_kobj);
 804         if (!swap_kobj) {
 805                 pr_err("failed to create swap kobject\n");
 806                 return -ENOMEM;
 807         }
 808         err = sysfs_create_group(swap_kobj, &swap_attr_group);
 809         if (err) {
 810                 pr_err("failed to register swap group\n");
 811                 goto delete_obj;
 812         }
 813         return 0;
 814
 815 delete_obj:
 816         kobject_put(swap_kobj);
 817         return err;
 818 }
 819 subsys_initcall(swap_init_sysfs);
 820 #endif