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
  27 /*
  28  * swapper_space is a fiction, retained to simplify the path through
  29  * vmscan's shrink_page_list.
  30  */
  31 static const struct address_space_operations swap_aops = {
  32         .writepage      = swap_writepage,
  33         .set_page_dirty = swap_set_page_dirty,
  34 #ifdef CONFIG_MIGRATION
  35         .migratepage    = migrate_page,
  36 #endif
  37 };
  38
  39 struct address_space *swapper_spaces[MAX_SWAPFILES] __read_mostly;
  40 static unsigned int nr_swapper_spaces[MAX_SWAPFILES] __read_mostly;
  41 static bool enable_vma_readahead __read_mostly = true;
  42
  43 #define SWAP_RA_WIN_SHIFT       (PAGE_SHIFT / 2)
  44 #define SWAP_RA_HITS_MASK       ((1UL << SWAP_RA_WIN_SHIFT) - 1)
  45 #define SWAP_RA_HITS_MAX        SWAP_RA_HITS_MASK
  46 #define SWAP_RA_WIN_MASK        (~PAGE_MASK & ~SWAP_RA_HITS_MASK)
  47
  48 #define SWAP_RA_HITS(v)         ((v) & SWAP_RA_HITS_MASK)
  49 #define SWAP_RA_WIN(v)          (((v) & SWAP_RA_WIN_MASK) >> SWAP_RA_WIN_SHIFT)
  50 #define SWAP_RA_ADDR(v)         ((v) & PAGE_MASK)
  51
  52 #define SWAP_RA_VAL(addr, win, hits)                            \
  53         (((addr) & PAGE_MASK) |                                 \
  54          (((win) << SWAP_RA_WIN_SHIFT) & SWAP_RA_WIN_MASK) |    \
  55          ((hits) & SWAP_RA_HITS_MASK))
  56
  57 /* Initial readahead hits is 4 to start up with a small window */
  58 #define GET_SWAP_RA_VAL(vma)                                    \
  59         (atomic_long_read(&(vma)->swap_readahead_info) ? : 4)
  60
  61 #define INC_CACHE_INFO(x)       do { swap_cache_info.x++; } while (0)
  62 #define ADD_CACHE_INFO(x, nr)   do { swap_cache_info.x += (nr); } while (0)
  63
  64 static struct {
  65         unsigned long add_total;
  66         unsigned long del_total;
  67         unsigned long find_success;
  68         unsigned long find_total;
  69 } swap_cache_info;
  70
  71 unsigned long total_swapcache_pages(void)
  72 {
  73         unsigned int i, j, nr;
  74         unsigned long ret = 0;
  75         struct address_space *spaces;
  76
  77         rcu_read_lock();
  78         for (i = 0; i < MAX_SWAPFILES; i++) {
  79                 /*
  80                  * The corresponding entries in nr_swapper_spaces and
  81                  * swapper_spaces will be reused only after at least
  82                  * one grace period.  So it is impossible for them
  83                  * belongs to different usage.
  84                  */
  85                 nr = nr_swapper_spaces[i];
  86                 spaces = rcu_dereference(swapper_spaces[i]);
  87                 if (!nr || !spaces)
  88                         continue;
  89                 for (j = 0; j < nr; j++)
  90                         ret += spaces[j].nrpages;
  91         }
  92         rcu_read_unlock();
  93         return ret;
  94 }
  95
  96 static atomic_t swapin_readahead_hits = ATOMIC_INIT(4);
  97
  98 void show_swap_cache_info(void)
  99 {
 100         printk("%lu pages in swap cache\n", total_swapcache_pages());
 101         printk("Swap cache stats: add %lu, delete %lu, find %lu/%lu\n",
 102                 swap_cache_info.add_total, swap_cache_info.del_total,
 103                 swap_cache_info.find_success, swap_cache_info.find_total);
 104         printk("Free swap  = %ldkB\n",
 105                 get_nr_swap_pages() << (PAGE_SHIFT - 10));
 106         printk("Total swap = %lukB\n", total_swap_pages << (PAGE_SHIFT - 10));
 107 }
 108
 109 /*
 110  * __add_to_swap_cache resembles add_to_page_cache_locked on swapper_space,
 111  * but sets SwapCache flag and private instead of mapping and index.
 112  */
 113 int __add_to_swap_cache(struct page *page, swp_entry_t entry)
 114 {
 115         int error, i, nr = hpage_nr_pages(page);
 116         struct address_space *address_space;
 117         pgoff_t idx = swp_offset(entry);
 118
 119         VM_BUG_ON_PAGE(!PageLocked(page), page);
 120         VM_BUG_ON_PAGE(PageSwapCache(page), page);
 121         VM_BUG_ON_PAGE(!PageSwapBacked(page), page);
 122
 123         page_ref_add(page, nr);
 124         SetPageSwapCache(page);
 125
 126         address_space = swap_address_space(entry);
 127         xa_lock_irq(&address_space->i_pages);
 128         for (i = 0; i < nr; i++) {
 129                 set_page_private(page + i, entry.val + i);
 130                 error = radix_tree_insert(&address_space->i_pages,
 131                                           idx + i, page + i);
 132                 if (unlikely(error))
 133                         break;
 134         }
 135         if (likely(!error)) {
 136                 address_space->nrpages += nr;
 137                 __mod_node_page_state(page_pgdat(page), NR_FILE_PAGES, nr);
 138                 ADD_CACHE_INFO(add_total, nr);
 139         } else {
 140                 /*
 141                  * Only the context which have set SWAP_HAS_CACHE flag
 142                  * would call add_to_swap_cache().
 143                  * So add_to_swap_cache() doesn't returns -EEXIST.
 144                  */
 145                 VM_BUG_ON(error == -EEXIST);
 146                 set_page_private(page + i, 0UL);
 147                 while (i--) {
 148                         radix_tree_delete(&address_space->i_pages, idx + i);
 149                         set_page_private(page + i, 0UL);
 150                 }
 151                 ClearPageSwapCache(page);
 152                 page_ref_sub(page, nr);
 153         }
 154         xa_unlock_irq(&address_space->i_pages);
 155
 156         return error;
 157 }
 158
 159
 160 int add_to_swap_cache(struct page *page, swp_entry_t entry, gfp_t gfp_mask)
 161 {
 162         int error;
 163
 164         error = radix_tree_maybe_preload_order(gfp_mask, compound_order(page));
 165         if (!error) {
 166                 error = __add_to_swap_cache(page, entry);
 167                 radix_tree_preload_end();
 168         }
 169         return error;
 170 }
 171
 172 /*
 173  * This must be called only on pages that have
 174  * been verified to be in the swap cache.
 175  */
 176 void __delete_from_swap_cache(struct page *page)
 177 {
 178         struct address_space *address_space;
 179         int i, nr = hpage_nr_pages(page);
 180         swp_entry_t entry;
 181         pgoff_t idx;
 182
 183         VM_BUG_ON_PAGE(!PageLocked(page), page);
 184         VM_BUG_ON_PAGE(!PageSwapCache(page), page);
 185         VM_BUG_ON_PAGE(PageWriteback(page), page);
 186
 187         entry.val = page_private(page);
 188         address_space = swap_address_space(entry);
 189         idx = swp_offset(entry);
 190         for (i = 0; i < nr; i++) {
 191                 radix_tree_delete(&address_space->i_pages, idx + i);
 192                 set_page_private(page + i, 0);
 193         }
 194         ClearPageSwapCache(page);
 195         address_space->nrpages -= nr;
 196         __mod_node_page_state(page_pgdat(page), NR_FILE_PAGES, -nr);
 197         ADD_CACHE_INFO(del_total, nr);
 198 }
 199
 200 /**
 201  * add_to_swap - allocate swap space for a page
 202  * @page: page we want to move to swap
 203  *
 204  * Allocate swap space for the page and add the page to the
 205  * swap cache.  Caller needs to hold the page lock.
 206  */
 207 int add_to_swap(struct page *page)
 208 {
 209         swp_entry_t entry;
 210         int err;
 211
 212         VM_BUG_ON_PAGE(!PageLocked(page), page);
 213         VM_BUG_ON_PAGE(!PageUptodate(page), page);
 214
 215         entry = get_swap_page(page);
 216         if (!entry.val)
 217                 return 0;
 218
 219         if (mem_cgroup_try_charge_swap(page, entry))
 220                 goto fail;
 221
 222         /*
 223          * Radix-tree node allocations from PF_MEMALLOC contexts could
 224          * completely exhaust the page allocator. __GFP_NOMEMALLOC
 225          * stops emergency reserves from being allocated.
 226          *
 227          * TODO: this could cause a theoretical memory reclaim
 228          * deadlock in the swap out path.
 229          */
 230         /*
 231          * Add it to the swap cache.
 232          */
 233         err = add_to_swap_cache(page, entry,
 234                         __GFP_HIGH|__GFP_NOMEMALLOC|__GFP_NOWARN);
 235         /* -ENOMEM radix-tree allocation failure */
 236         if (err)
 237                 /*
 238                  * add_to_swap_cache() doesn't return -EEXIST, so we can safely
 239                  * clear SWAP_HAS_CACHE flag.
 240                  */
 241                 goto fail;
 242         /*
 243          * Normally the page will be dirtied in unmap because its pte should be
 244          * dirty. A special case is MADV_FREE page. The page'e pte could have
 245          * dirty bit cleared but the page's SwapBacked bit is still set because
 246          * clearing the dirty bit and SwapBacked bit has no lock protected. For
 247          * such page, unmap will not set dirty bit for it, so page reclaim will
 248          * not write the page out. This can cause data corruption when the page
 249          * is swap in later. Always setting the dirty bit for the page solves
 250          * the problem.
 251          */
 252         set_page_dirty(page);
 253
 254         return 1;
 255
 256 fail:
 257         put_swap_page(page, entry);
 258         return 0;
 259 }
 260
 261 /*
 262  * This must be called only on pages that have
 263  * been verified to be in the swap cache and locked.
 264  * It will never put the page into the free list,
 265  * the caller has a reference on the page.
 266  */
 267 void delete_from_swap_cache(struct page *page)
 268 {
 269         swp_entry_t entry;
 270         struct address_space *address_space;
 271
 272         entry.val = page_private(page);
 273
 274         address_space = swap_address_space(entry);
 275         xa_lock_irq(&address_space->i_pages);
 276         __delete_from_swap_cache(page);
 277         xa_unlock_irq(&address_space->i_pages);
 278
 279         put_swap_page(page, entry);
 280         page_ref_sub(page, hpage_nr_pages(page));
 281 }
 282
 283 /*
 284  * If we are the only user, then try to free up the swap cache.
 285  *
 286  * Its ok to check for PageSwapCache without the page lock
 287  * here because we are going to recheck again inside
 288  * try_to_free_swap() _with_ the lock.
 289  *                                      - Marcelo
 290  */
 291 static inline void free_swap_cache(struct page *page)
 292 {
 293         if (PageSwapCache(page) && !page_mapped(page) && trylock_page(page)) {
 294                 try_to_free_swap(page);
 295                 unlock_page(page);
 296         }
 297 }
 298
 299 /*
 300  * Perform a free_page(), also freeing any swap cache associated with
 301  * this page if it is the last user of the page.
 302  */
 303 void free_page_and_swap_cache(struct page *page)
 304 {
 305         free_swap_cache(page);
 306         if (!is_huge_zero_page(page))
 307                 put_page(page);
 308 }
 309
 310 /*
 311  * Passed an array of pages, drop them all from swapcache and then release
 312  * them.  They are removed from the LRU and freed if this is their last use.
 313  */
 314 void free_pages_and_swap_cache(struct page **pages, int nr)
 315 {
 316         struct page **pagep = pages;
 317         int i;
 318
 319         lru_add_drain();
 320         for (i = 0; i < nr; i++)
 321                 free_swap_cache(pagep[i]);
 322         release_pages(pagep, nr);
 323 }
 324
 325 static inline bool swap_use_vma_readahead(void)
 326 {
 327         return READ_ONCE(enable_vma_readahead) && !atomic_read(&nr_rotate_swap);
 328 }
 329
 330 /*
 331  * Lookup a swap entry in the swap cache. A found page will be returned
 332  * unlocked and with its refcount incremented - we rely on the kernel
 333  * lock getting page table operations atomic even if we drop the page
 334  * lock before returning.
 335  */
 336 struct page *lookup_swap_cache(swp_entry_t entry, struct vm_area_struct *vma,
 337                                unsigned long addr)
 338 {
 339         struct page *page;
 340
 341         page = find_get_page(swap_address_space(entry), swp_offset(entry));
 342
 343         INC_CACHE_INFO(find_total);
 344         if (page) {
 345                 bool vma_ra = swap_use_vma_readahead();
 346                 bool readahead;
 347
 348                 INC_CACHE_INFO(find_success);
 349                 /*
 350                  * At the moment, we don't support PG_readahead for anon THP
 351                  * so let's bail out rather than confusing the readahead stat.
 352                  */
 353                 if (unlikely(PageTransCompound(page)))
 354                         return page;
 355
 356                 readahead = TestClearPageReadahead(page);
 357                 if (vma && vma_ra) {
 358                         unsigned long ra_val;
 359                         int win, hits;
 360
 361                         ra_val = GET_SWAP_RA_VAL(vma);
 362                         win = SWAP_RA_WIN(ra_val);
 363                         hits = SWAP_RA_HITS(ra_val);
 364                         if (readahead)
 365                                 hits = min_t(int, hits + 1, SWAP_RA_HITS_MAX);
 366                         atomic_long_set(&vma->swap_readahead_info,
 367                                         SWAP_RA_VAL(addr, win, hits));
 368                 }
 369
 370                 if (readahead) {
 371                         count_vm_event(SWAP_RA_HIT);
 372                         if (!vma || !vma_ra)
 373                                 atomic_inc(&swapin_readahead_hits);
 374                 }
 375         }
 376
 377         return page;
 378 }
 379
 380 struct page *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
 381                         struct vm_area_struct *vma, unsigned long addr,
 382                         bool *new_page_allocated)
 383 {
 384         struct page *found_page, *new_page = NULL;
 385         struct address_space *swapper_space = swap_address_space(entry);
 386         int err;
 387         *new_page_allocated = false;
 388
 389         do {
 390                 /*
 391                  * First check the swap cache.  Since this is normally
 392                  * called after lookup_swap_cache() failed, re-calling
 393                  * that would confuse statistics.
 394                  */
 395                 found_page = find_get_page(swapper_space, swp_offset(entry));
 396                 if (found_page)
 397                         break;
 398
 399                 /*
 400                  * Just skip read ahead for unused swap slot.
 401                  * During swap_off when swap_slot_cache is disabled,
 402                  * we have to handle the race between putting
 403                  * swap entry in swap cache and marking swap slot
 404                  * as SWAP_HAS_CACHE.  That's done in later part of code or
 405                  * else swap_off will be aborted if we return NULL.
 406                  */
 407                 if (!__swp_swapcount(entry) && swap_slot_cache_enabled)
 408                         break;
 409
 410                 /*
 411                  * Get a new page to read into from swap.
 412                  */
 413                 if (!new_page) {
 414                         new_page = alloc_page_vma(gfp_mask, vma, addr);
 415                         if (!new_page)
 416                                 break;          /* Out of memory */
 417                 }
 418
 419                 /*
 420                  * call radix_tree_preload() while we can wait.
 421                  */
 422                 err = radix_tree_maybe_preload(gfp_mask & GFP_KERNEL);
 423                 if (err)
 424                         break;
 425
 426                 /*
 427                  * Swap entry may have been freed since our caller observed it.
 428                  */
 429                 err = swapcache_prepare(entry);
 430                 if (err == -EEXIST) {
 431                         radix_tree_preload_end();
 432                         /*
 433                          * We might race against get_swap_page() and stumble
 434                          * across a SWAP_HAS_CACHE swap_map entry whose page
 435                          * has not been brought into the swapcache yet.
 436                          */
 437                         cond_resched();
 438                         continue;
 439                 }
 440                 if (err) {              /* swp entry is obsolete ? */
 441                         radix_tree_preload_end();
 442                         break;
 443                 }
 444
 445                 /* May fail (-ENOMEM) if radix-tree node allocation failed. */
 446                 __SetPageLocked(new_page);
 447                 __SetPageSwapBacked(new_page);
 448                 err = __add_to_swap_cache(new_page, entry);
 449                 if (likely(!err)) {
 450                         radix_tree_preload_end();
 451                         /*
 452                          * Initiate read into locked page and return.
 453                          */
 454                         lru_cache_add_anon(new_page);
 455                         *new_page_allocated = true;
 456                         return new_page;
 457                 }
 458                 radix_tree_preload_end();
 459                 __ClearPageLocked(new_page);
 460                 /*
 461                  * add_to_swap_cache() doesn't return -EEXIST, so we can safely
 462                  * clear SWAP_HAS_CACHE flag.
 463                  */
 464                 put_swap_page(new_page, entry);
 465         } while (err != -ENOMEM);
 466
 467         if (new_page)
 468                 put_page(new_page);
 469         return found_page;
 470 }
 471
 472 /*
 473  * Locate a page of swap in physical memory, reserving swap cache space
 474  * and reading the disk if it is not already cached.
 475  * A failure return means that either the page allocation failed or that
 476  * the swap entry is no longer in use.
 477  */
 478 struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
 479                 struct vm_area_struct *vma, unsigned long addr, bool do_poll)
 480 {
 481         bool page_was_allocated;
 482         struct page *retpage = __read_swap_cache_async(entry, gfp_mask,
 483                         vma, addr, &page_was_allocated);
 484
 485         if (page_was_allocated)
 486                 swap_readpage(retpage, do_poll);
 487
 488         return retpage;
 489 }
 490
 491 static unsigned int __swapin_nr_pages(unsigned long prev_offset,
 492                                       unsigned long offset,
 493                                       int hits,
 494                                       int max_pages,
 495                                       int prev_win)
 496 {
 497         unsigned int pages, last_ra;
 498
 499         /*
 500          * This heuristic has been found to work well on both sequential and
 501          * random loads, swapping to hard disk or to SSD: please don't ask
 502          * what the "+ 2" means, it just happens to work well, that's all.
 503          */
 504         pages = hits + 2;
 505         if (pages == 2) {
 506                 /*
 507                  * We can have no readahead hits to judge by: but must not get
 508                  * stuck here forever, so check for an adjacent offset instead
 509                  * (and don't even bother to check whether swap type is same).
 510                  */
 511                 if (offset != prev_offset + 1 && offset != prev_offset - 1)
 512                         pages = 1;
 513         } else {
 514                 unsigned int roundup = 4;
 515                 while (roundup < pages)
 516                         roundup <<= 1;
 517                 pages = roundup;
 518         }
 519
 520         if (pages > max_pages)
 521                 pages = max_pages;
 522
 523         /* Don't shrink readahead too fast */
 524         last_ra = prev_win / 2;
 525         if (pages < last_ra)
 526                 pages = last_ra;
 527
 528         return pages;
 529 }
 530
 531 static unsigned long swapin_nr_pages(unsigned long offset)
 532 {
 533         static unsigned long prev_offset;
 534         unsigned int hits, pages, max_pages;
 535         static atomic_t last_readahead_pages;
 536
 537         max_pages = 1 << READ_ONCE(page_cluster);
 538         if (max_pages <= 1)
 539                 return 1;
 540
 541         hits = atomic_xchg(&swapin_readahead_hits, 0);
 542         pages = __swapin_nr_pages(prev_offset, offset, hits, max_pages,
 543                                   atomic_read(&last_readahead_pages));
 544         if (!hits)
 545                 prev_offset = offset;
 546         atomic_set(&last_readahead_pages, pages);
 547
 548         return pages;
 549 }
 550
 551 /**
 552  * swap_cluster_readahead - swap in pages in hope we need them soon
 553  * @entry: swap entry of this memory
 554  * @gfp_mask: memory allocation flags
 555  * @vmf: fault information
 556  *
 557  * Returns the struct page for entry and addr, after queueing swapin.
 558  *
 559  * Primitive swap readahead code. We simply read an aligned block of
 560  * (1 << page_cluster) entries in the swap area. This method is chosen
 561  * because it doesn't cost us any seek time.  We also make sure to queue
 562  * the 'original' request together with the readahead ones...
 563  *
 564  * This has been extended to use the NUMA policies from the mm triggering
 565  * the readahead.
 566  *
 567  * Caller must hold down_read on the vma->vm_mm if vmf->vma is not NULL.
 568  */
 569 struct page *swap_cluster_readahead(swp_entry_t entry, gfp_t gfp_mask,
 570                                 struct vm_fault *vmf)
 571 {
 572         struct page *page;
 573         unsigned long entry_offset = swp_offset(entry);
 574         unsigned long offset = entry_offset;
 575         unsigned long start_offset, end_offset;
 576         unsigned long mask;
 577         struct swap_info_struct *si = swp_swap_info(entry);
 578         struct blk_plug plug;
 579         bool do_poll = true, page_allocated;
 580         struct vm_area_struct *vma = vmf->vma;
 581         unsigned long addr = vmf->address;
 582
 583         mask = swapin_nr_pages(offset) - 1;
 584         if (!mask)
 585                 goto skip;
 586
 587         do_poll = false;
 588         /* Read a page_cluster sized and aligned cluster around offset. */
 589         start_offset = offset & ~mask;
 590         end_offset = offset | mask;
 591         if (!start_offset)      /* First page is swap header. */
 592                 start_offset++;
 593         if (end_offset >= si->max)
 594                 end_offset = si->max - 1;
 595
 596         blk_start_plug(&plug);
 597         for (offset = start_offset; offset <= end_offset ; offset++) {
 598                 /* Ok, do the async read-ahead now */
 599                 page = __read_swap_cache_async(
 600                         swp_entry(swp_type(entry), offset),
 601                         gfp_mask, vma, addr, &page_allocated);
 602                 if (!page)
 603                         continue;
 604                 if (page_allocated) {
 605                         swap_readpage(page, false);
 606                         if (offset != entry_offset) {
 607                                 SetPageReadahead(page);
 608                                 count_vm_event(SWAP_RA);
 609                         }
 610                 }
 611                 put_page(page);
 612         }
 613         blk_finish_plug(&plug);
 614
 615         lru_add_drain();        /* Push any new pages onto the LRU now */
 616 skip:
 617         return read_swap_cache_async(entry, gfp_mask, vma, addr, do_poll);
 618 }
 619
 620 int init_swap_address_space(unsigned int type, unsigned long nr_pages)
 621 {
 622         struct address_space *spaces, *space;
 623         unsigned int i, nr;
 624
 625         nr = DIV_ROUND_UP(nr_pages, SWAP_ADDRESS_SPACE_PAGES);
 626         spaces = kvzalloc(sizeof(struct address_space) * nr, GFP_KERNEL);
 627         if (!spaces)
 628                 return -ENOMEM;
 629         for (i = 0; i < nr; i++) {
 630                 space = spaces + i;
 631                 INIT_RADIX_TREE(&space->i_pages, GFP_ATOMIC|__GFP_NOWARN);
 632                 atomic_set(&space->i_mmap_writable, 0);
 633                 space->a_ops = &swap_aops;
 634                 /* swap cache doesn't use writeback related tags */
 635                 mapping_set_no_writeback_tags(space);
 636         }
 637         nr_swapper_spaces[type] = nr;
 638         rcu_assign_pointer(swapper_spaces[type], spaces);
 639
 640         return 0;
 641 }
 642
 643 void exit_swap_address_space(unsigned int type)
 644 {
 645         struct address_space *spaces;
 646
 647         spaces = swapper_spaces[type];
 648         nr_swapper_spaces[type] = 0;
 649         rcu_assign_pointer(swapper_spaces[type], NULL);
 650         synchronize_rcu();
 651         kvfree(spaces);
 652 }
 653
 654 static inline void swap_ra_clamp_pfn(struct vm_area_struct *vma,
 655                                      unsigned long faddr,
 656                                      unsigned long lpfn,
 657                                      unsigned long rpfn,
 658                                      unsigned long *start,
 659                                      unsigned long *end)
 660 {
 661         *start = max3(lpfn, PFN_DOWN(vma->vm_start),
 662                       PFN_DOWN(faddr & PMD_MASK));
 663         *end = min3(rpfn, PFN_DOWN(vma->vm_end),
 664                     PFN_DOWN((faddr & PMD_MASK) + PMD_SIZE));
 665 }
 666
 667 static void swap_ra_info(struct vm_fault *vmf,
 668                         struct vma_swap_readahead *ra_info)
 669 {
 670         struct vm_area_struct *vma = vmf->vma;
 671         unsigned long ra_val;
 672         swp_entry_t entry;
 673         unsigned long faddr, pfn, fpfn;
 674         unsigned long start, end;
 675         pte_t *pte, *orig_pte;
 676         unsigned int max_win, hits, prev_win, win, left;
 677 #ifndef CONFIG_64BIT
 678         pte_t *tpte;
 679 #endif
 680
 681         max_win = 1 << min_t(unsigned int, READ_ONCE(page_cluster),
 682                              SWAP_RA_ORDER_CEILING);
 683         if (max_win == 1) {
 684                 ra_info->win = 1;
 685                 return;
 686         }
 687
 688         faddr = vmf->address;
 689         orig_pte = pte = pte_offset_map(vmf->pmd, faddr);
 690         entry = pte_to_swp_entry(*pte);
 691         if ((unlikely(non_swap_entry(entry)))) {
 692                 pte_unmap(orig_pte);
 693                 return;
 694         }
 695
 696         fpfn = PFN_DOWN(faddr);
 697         ra_val = GET_SWAP_RA_VAL(vma);
 698         pfn = PFN_DOWN(SWAP_RA_ADDR(ra_val));
 699         prev_win = SWAP_RA_WIN(ra_val);
 700         hits = SWAP_RA_HITS(ra_val);
 701         ra_info->win = win = __swapin_nr_pages(pfn, fpfn, hits,
 702                                                max_win, prev_win);
 703         atomic_long_set(&vma->swap_readahead_info,
 704                         SWAP_RA_VAL(faddr, win, 0));
 705
 706         if (win == 1) {
 707                 pte_unmap(orig_pte);
 708                 return;
 709         }
 710
 711         /* Copy the PTEs because the page table may be unmapped */
 712         if (fpfn == pfn + 1)
 713                 swap_ra_clamp_pfn(vma, faddr, fpfn, fpfn + win, &start, &end);
 714         else if (pfn == fpfn + 1)
 715                 swap_ra_clamp_pfn(vma, faddr, fpfn - win + 1, fpfn + 1,
 716                                   &start, &end);
 717         else {
 718                 left = (win - 1) / 2;
 719                 swap_ra_clamp_pfn(vma, faddr, fpfn - left, fpfn + win - left,
 720                                   &start, &end);
 721         }
 722         ra_info->nr_pte = end - start;
 723         ra_info->offset = fpfn - start;
 724         pte -= ra_info->offset;
 725 #ifdef CONFIG_64BIT
 726         ra_info->ptes = pte;
 727 #else
 728         tpte = ra_info->ptes;
 729         for (pfn = start; pfn != end; pfn++)
 730                 *tpte++ = *pte++;
 731 #endif
 732         pte_unmap(orig_pte);
 733 }
 734
 735 static struct page *swap_vma_readahead(swp_entry_t fentry, gfp_t gfp_mask,
 736                                        struct vm_fault *vmf)
 737 {
 738         struct blk_plug plug;
 739         struct vm_area_struct *vma = vmf->vma;
 740         struct page *page;
 741         pte_t *pte, pentry;
 742         swp_entry_t entry;
 743         unsigned int i;
 744         bool page_allocated;
 745         struct vma_swap_readahead ra_info = {0,};
 746
 747         swap_ra_info(vmf, &ra_info);
 748         if (ra_info.win == 1)
 749                 goto skip;
 750
 751         blk_start_plug(&plug);
 752         for (i = 0, pte = ra_info.ptes; i < ra_info.nr_pte;
 753              i++, pte++) {
 754                 pentry = *pte;
 755                 if (pte_none(pentry))
 756                         continue;
 757                 if (pte_present(pentry))
 758                         continue;
 759                 entry = pte_to_swp_entry(pentry);
 760                 if (unlikely(non_swap_entry(entry)))
 761                         continue;
 762                 page = __read_swap_cache_async(entry, gfp_mask, vma,
 763                                                vmf->address, &page_allocated);
 764                 if (!page)
 765                         continue;
 766                 if (page_allocated) {
 767                         swap_readpage(page, false);
 768                         if (i != ra_info.offset) {
 769                                 SetPageReadahead(page);
 770                                 count_vm_event(SWAP_RA);
 771                         }
 772                 }
 773                 put_page(page);
 774         }
 775         blk_finish_plug(&plug);
 776         lru_add_drain();
 777 skip:
 778         return read_swap_cache_async(fentry, gfp_mask, vma, vmf->address,
 779                                      ra_info.win == 1);
 780 }
 781
 782 /**
 783  * swapin_readahead - swap in pages in hope we need them soon
 784  * @entry: swap entry of this memory
 785  * @gfp_mask: memory allocation flags
 786  * @vmf: fault information
 787  *
 788  * Returns the struct page for entry and addr, after queueing swapin.
 789  *
 790  * It's a main entry function for swap readahead. By the configuration,
 791  * it will read ahead blocks by cluster-based(ie, physical disk based)
 792  * or vma-based(ie, virtual address based on faulty address) readahead.
 793  */
 794 struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
 795                                 struct vm_fault *vmf)
 796 {
 797         return swap_use_vma_readahead() ?
 798                         swap_vma_readahead(entry, gfp_mask, vmf) :
 799                         swap_cluster_readahead(entry, gfp_mask, vmf);
 800 }
 801
 802 #ifdef CONFIG_SYSFS
 803 static ssize_t vma_ra_enabled_show(struct kobject *kobj,
 804                                      struct kobj_attribute *attr, char *buf)
 805 {
 806         return sprintf(buf, "%s\n", enable_vma_readahead ? "true" : "false");
 807 }
 808 static ssize_t vma_ra_enabled_store(struct kobject *kobj,
 809                                       struct kobj_attribute *attr,
 810                                       const char *buf, size_t count)
 811 {
 812         if (!strncmp(buf, "true", 4) || !strncmp(buf, "1", 1))
 813                 enable_vma_readahead = true;
 814         else if (!strncmp(buf, "false", 5) || !strncmp(buf, "0", 1))
 815                 enable_vma_readahead = false;
 816         else
 817                 return -EINVAL;
 818
 819         return count;
 820 }
 821 static struct kobj_attribute vma_ra_enabled_attr =
 822         __ATTR(vma_ra_enabled, 0644, vma_ra_enabled_show,
 823                vma_ra_enabled_store);
 824
 825 static struct attribute *swap_attrs[] = {
 826         &vma_ra_enabled_attr.attr,
 827         NULL,
 828 };
 829
 830 static struct attribute_group swap_attr_group = {
 831         .attrs = swap_attrs,
 832 };
 833
 834 static int __init swap_init_sysfs(void)
 835 {
 836         int err;
 837         struct kobject *swap_kobj;
 838
 839         swap_kobj = kobject_create_and_add("swap", mm_kobj);
 840         if (!swap_kobj) {
 841                 pr_err("failed to create swap kobject\n");
 842                 return -ENOMEM;
 843         }
 844         err = sysfs_create_group(swap_kobj, &swap_attr_group);
 845         if (err) {
 846                 pr_err("failed to register swap group\n");
 847                 goto delete_obj;
 848         }
 849         return 0;
 850
 851 delete_obj:
 852         kobject_put(swap_kobj);
 853         return err;
 854 }
 855 subsys_initcall(swap_init_sysfs);
 856 #endif