root/mm/swap_state.c

DEFINITIONS

1. total_swapcache_pages
2. show_swap_cache_info
3. add_to_swap_cache
4. __delete_from_swap_cache
5. add_to_swap
6. delete_from_swap_cache
7. free_swap_cache
8. free_page_and_swap_cache
9. free_pages_and_swap_cache
10. swap_use_vma_readahead
11. lookup_swap_cache
12. __read_swap_cache_async
13. read_swap_cache_async
14. __swapin_nr_pages
15. swapin_nr_pages
16. swap_cluster_readahead
17. init_swap_address_space
18. exit_swap_address_space
19. swap_ra_clamp_pfn
20. swap_ra_info
21. swap_vma_readahead
22. swapin_readahead
23. vma_ra_enabled_show
24. vma_ra_enabled_store
25. swap_init_sysfs

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