mm/swap_state.c

   1 /*
   2  *  linux/mm/swap_state.c
   3  *
   4  *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
   5  *  Swap reorganised 29.12.95, Stephen Tweedie
   6  *
   7  *  Rewritten to use page cache, (C) 1998 Stephen Tweedie
   8  */
   9 #include <linux/mm.h>
  10 #include <linux/gfp.h>
  11 #include <linux/kernel_stat.h>
  12 #include <linux/swap.h>
  13 #include <linux/swapops.h>
  14 #include <linux/init.h>
  15 #include <linux/pagemap.h>
  16 #include <linux/backing-dev.h>
  17 #include <linux/blkdev.h>
  18 #include <linux/pagevec.h>
  19 #include <linux/migrate.h>
  20
  21 #include <asm/pgtable.h>
  22
  23 /*
  24  * swapper_space is a fiction, retained to simplify the path through
  25  * vmscan's shrink_page_list.
  26  */
  27 static const struct address_space_operations swap_aops = {
  28         .writepage      = swap_writepage,
  29         .set_page_dirty = swap_set_page_dirty,
  30 #ifdef CONFIG_MIGRATION
  31         .migratepage    = migrate_page,
  32 #endif
  33 };
  34
  35 struct address_space swapper_spaces[MAX_SWAPFILES] = {
  36         [0 ... MAX_SWAPFILES - 1] = {
  37                 .page_tree      = RADIX_TREE_INIT(GFP_ATOMIC|__GFP_NOWARN),
  38                 .i_mmap_writable = ATOMIC_INIT(0),
  39                 .a_ops          = &swap_aops,
  40         }
  41 };
  42
  43 #define INC_CACHE_INFO(x)       do { swap_cache_info.x++; } while (0)
  44
  45 static struct {
  46         unsigned long add_total;
  47         unsigned long del_total;
  48         unsigned long find_success;
  49         unsigned long find_total;
  50 } swap_cache_info;
  51
  52 unsigned long total_swapcache_pages(void)
  53 {
  54         int i;
  55         unsigned long ret = 0;
  56
  57         for (i = 0; i < MAX_SWAPFILES; i++)
  58                 ret += swapper_spaces[i].nrpages;
  59         return ret;
  60 }
  61
  62 static atomic_t swapin_readahead_hits = ATOMIC_INIT(4);
  63
  64 void show_swap_cache_info(void)
  65 {
  66         printk("%lu pages in swap cache\n", total_swapcache_pages());
  67         printk("Swap cache stats: add %lu, delete %lu, find %lu/%lu\n",
  68                 swap_cache_info.add_total, swap_cache_info.del_total,
  69                 swap_cache_info.find_success, swap_cache_info.find_total);
  70         printk("Free swap  = %ldkB\n",
  71                 get_nr_swap_pages() << (PAGE_SHIFT - 10));
  72         printk("Total swap = %lukB\n", total_swap_pages << (PAGE_SHIFT - 10));
  73 }
  74
  75 /*
  76  * __add_to_swap_cache resembles add_to_page_cache_locked on swapper_space,
  77  * but sets SwapCache flag and private instead of mapping and index.
  78  */
  79 int __add_to_swap_cache(struct page *page, swp_entry_t entry)
  80 {
  81         int error;
  82         struct address_space *address_space;
  83
  84         VM_BUG_ON_PAGE(!PageLocked(page), page);
  85         VM_BUG_ON_PAGE(PageSwapCache(page), page);
  86         VM_BUG_ON_PAGE(!PageSwapBacked(page), page);
  87
  88         page_cache_get(page);
  89         SetPageSwapCache(page);
  90         set_page_private(page, entry.val);
  91
  92         address_space = swap_address_space(entry);
  93         spin_lock_irq(&address_space->tree_lock);
  94         error = radix_tree_insert(&address_space->page_tree,
  95                                         entry.val, page);
  96         if (likely(!error)) {
  97                 address_space->nrpages++;
  98                 __inc_zone_page_state(page, NR_FILE_PAGES);
  99                 INC_CACHE_INFO(add_total);
 100         }
 101         spin_unlock_irq(&address_space->tree_lock);
 102
 103         if (unlikely(error)) {
 104                 /*
 105                  * Only the context which have set SWAP_HAS_CACHE flag
 106                  * would call add_to_swap_cache().
 107                  * So add_to_swap_cache() doesn't returns -EEXIST.
 108                  */
 109                 VM_BUG_ON(error == -EEXIST);
 110                 set_page_private(page, 0UL);
 111                 ClearPageSwapCache(page);
 112                 page_cache_release(page);
 113         }
 114
 115         return error;
 116 }
 117
 118
 119 int add_to_swap_cache(struct page *page, swp_entry_t entry, gfp_t gfp_mask)
 120 {
 121         int error;
 122
 123         error = radix_tree_maybe_preload(gfp_mask);
 124         if (!error) {
 125                 error = __add_to_swap_cache(page, entry);
 126                 radix_tree_preload_end();
 127         }
 128         return error;
 129 }
 130
 131 /*
 132  * This must be called only on pages that have
 133  * been verified to be in the swap cache.
 134  */
 135 void __delete_from_swap_cache(struct page *page)
 136 {
 137         swp_entry_t entry;
 138         struct address_space *address_space;
 139
 140         VM_BUG_ON_PAGE(!PageLocked(page), page);
 141         VM_BUG_ON_PAGE(!PageSwapCache(page), page);
 142         VM_BUG_ON_PAGE(PageWriteback(page), page);
 143
 144         entry.val = page_private(page);
 145         address_space = swap_address_space(entry);
 146         radix_tree_delete(&address_space->page_tree, page_private(page));
 147         set_page_private(page, 0);
 148         ClearPageSwapCache(page);
 149         address_space->nrpages--;
 150         __dec_zone_page_state(page, NR_FILE_PAGES);
 151         INC_CACHE_INFO(del_total);
 152 }
 153
 154 /**
 155  * add_to_swap - allocate swap space for a page
 156  * @page: page we want to move to swap
 157  *
 158  * Allocate swap space for the page and add the page to the
 159  * swap cache.  Caller needs to hold the page lock.
 160  */
 161 int add_to_swap(struct page *page, struct list_head *list)
 162 {
 163         swp_entry_t entry;
 164         int err;
 165
 166         VM_BUG_ON_PAGE(!PageLocked(page), page);
 167         VM_BUG_ON_PAGE(!PageUptodate(page), page);
 168
 169         entry = get_swap_page();
 170         if (!entry.val)
 171                 return 0;
 172
 173         if (unlikely(PageTransHuge(page)))
 174                 if (unlikely(split_huge_page_to_list(page, list))) {
 175                         swapcache_free(entry);
 176                         return 0;
 177                 }
 178
 179         /*
 180          * Radix-tree node allocations from PF_MEMALLOC contexts could
 181          * completely exhaust the page allocator. __GFP_NOMEMALLOC
 182          * stops emergency reserves from being allocated.
 183          *
 184          * TODO: this could cause a theoretical memory reclaim
 185          * deadlock in the swap out path.
 186          */
 187         /*
 188          * Add it to the swap cache.
 189          */
 190         err = add_to_swap_cache(page, entry,
 191                         __GFP_HIGH|__GFP_NOMEMALLOC|__GFP_NOWARN);
 192
 193         if (!err) {
 194                 return 1;
 195         } else {        /* -ENOMEM radix-tree allocation failure */
 196                 /*
 197                  * add_to_swap_cache() doesn't return -EEXIST, so we can safely
 198                  * clear SWAP_HAS_CACHE flag.
 199                  */
 200                 swapcache_free(entry);
 201                 return 0;
 202         }
 203 }
 204
 205 /*
 206  * This must be called only on pages that have
 207  * been verified to be in the swap cache and locked.
 208  * It will never put the page into the free list,
 209  * the caller has a reference on the page.
 210  */
 211 void delete_from_swap_cache(struct page *page)
 212 {
 213         swp_entry_t entry;
 214         struct address_space *address_space;
 215
 216         entry.val = page_private(page);
 217
 218         address_space = swap_address_space(entry);
 219         spin_lock_irq(&address_space->tree_lock);
 220         __delete_from_swap_cache(page);
 221         spin_unlock_irq(&address_space->tree_lock);
 222
 223         swapcache_free(entry);
 224         page_cache_release(page);
 225 }
 226
 227 /*
 228  * If we are the only user, then try to free up the swap cache.
 229  *
 230  * Its ok to check for PageSwapCache without the page lock
 231  * here because we are going to recheck again inside
 232  * try_to_free_swap() _with_ the lock.
 233  *                                      - Marcelo
 234  */
 235 static inline void free_swap_cache(struct page *page)
 236 {
 237         if (PageSwapCache(page) && !page_mapped(page) && trylock_page(page)) {
 238                 try_to_free_swap(page);
 239                 unlock_page(page);
 240         }
 241 }
 242
 243 /*
 244  * Perform a free_page(), also freeing any swap cache associated with
 245  * this page if it is the last user of the page.
 246  */
 247 void free_page_and_swap_cache(struct page *page)
 248 {
 249         free_swap_cache(page);
 250         page_cache_release(page);
 251 }
 252
 253 /*
 254  * Passed an array of pages, drop them all from swapcache and then release
 255  * them.  They are removed from the LRU and freed if this is their last use.
 256  */
 257 void free_pages_and_swap_cache(struct page **pages, int nr)
 258 {
 259         struct page **pagep = pages;
 260         int i;
 261
 262         lru_add_drain();
 263         for (i = 0; i < nr; i++)
 264                 free_swap_cache(pagep[i]);
 265         release_pages(pagep, nr, false);
 266 }
 267
 268 /*
 269  * Lookup a swap entry in the swap cache. A found page will be returned
 270  * unlocked and with its refcount incremented - we rely on the kernel
 271  * lock getting page table operations atomic even if we drop the page
 272  * lock before returning.
 273  */
 274 struct page * lookup_swap_cache(swp_entry_t entry)
 275 {
 276         struct page *page;
 277
 278         page = find_get_page(swap_address_space(entry), entry.val);
 279
 280         if (page) {
 281                 INC_CACHE_INFO(find_success);
 282                 if (TestClearPageReadahead(page))
 283                         atomic_inc(&swapin_readahead_hits);
 284         }
 285
 286         INC_CACHE_INFO(find_total);
 287         return page;
 288 }
 289
 290 struct page *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
 291                         struct vm_area_struct *vma, unsigned long addr,
 292                         bool *new_page_allocated)
 293 {
 294         struct page *found_page, *new_page = NULL;
 295         struct address_space *swapper_space = swap_address_space(entry);
 296         int err;
 297         *new_page_allocated = false;
 298
 299         do {
 300                 /*
 301                  * First check the swap cache.  Since this is normally
 302                  * called after lookup_swap_cache() failed, re-calling
 303                  * that would confuse statistics.
 304                  */
 305                 found_page = find_get_page(swapper_space, entry.val);
 306                 if (found_page)
 307                         break;
 308
 309                 /*
 310                  * Get a new page to read into from swap.
 311                  */
 312                 if (!new_page) {
 313                         new_page = alloc_page_vma(gfp_mask, vma, addr);
 314                         if (!new_page)
 315                                 break;          /* Out of memory */
 316                 }
 317
 318                 /*
 319                  * call radix_tree_preload() while we can wait.
 320                  */
 321                 err = radix_tree_maybe_preload(gfp_mask & GFP_KERNEL);
 322                 if (err)
 323                         break;
 324
 325                 /*
 326                  * Swap entry may have been freed since our caller observed it.
 327                  */
 328                 err = swapcache_prepare(entry);
 329                 if (err == -EEXIST) {
 330                         radix_tree_preload_end();
 331                         /*
 332                          * We might race against get_swap_page() and stumble
 333                          * across a SWAP_HAS_CACHE swap_map entry whose page
 334                          * has not been brought into the swapcache yet, while
 335                          * the other end is scheduled away waiting on discard
 336                          * I/O completion at scan_swap_map().
 337                          *
 338                          * In order to avoid turning this transitory state
 339                          * into a permanent loop around this -EEXIST case
 340                          * if !CONFIG_PREEMPT and the I/O completion happens
 341                          * to be waiting on the CPU waitqueue where we are now
 342                          * busy looping, we just conditionally invoke the
 343                          * scheduler here, if there are some more important
 344                          * tasks to run.
 345                          */
 346                         cond_resched();
 347                         continue;
 348                 }
 349                 if (err) {              /* swp entry is obsolete ? */
 350                         radix_tree_preload_end();
 351                         break;
 352                 }
 353
 354                 /* May fail (-ENOMEM) if radix-tree node allocation failed. */
 355                 __SetPageLocked(new_page);
 356                 SetPageSwapBacked(new_page);
 357                 err = __add_to_swap_cache(new_page, entry);
 358                 if (likely(!err)) {
 359                         radix_tree_preload_end();
 360                         /*
 361                          * Initiate read into locked page and return.
 362                          */
 363                         lru_cache_add_anon(new_page);
 364                         *new_page_allocated = true;
 365                         return new_page;
 366                 }
 367                 radix_tree_preload_end();
 368                 ClearPageSwapBacked(new_page);
 369                 __ClearPageLocked(new_page);
 370                 /*
 371                  * add_to_swap_cache() doesn't return -EEXIST, so we can safely
 372                  * clear SWAP_HAS_CACHE flag.
 373                  */
 374                 swapcache_free(entry);
 375         } while (err != -ENOMEM);
 376
 377         if (new_page)
 378                 page_cache_release(new_page);
 379         return found_page;
 380 }
 381
 382 /*
 383  * Locate a page of swap in physical memory, reserving swap cache space
 384  * and reading the disk if it is not already cached.
 385  * A failure return means that either the page allocation failed or that
 386  * the swap entry is no longer in use.
 387  */
 388 struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
 389                         struct vm_area_struct *vma, unsigned long addr)
 390 {
 391         bool page_was_allocated;
 392         struct page *retpage = __read_swap_cache_async(entry, gfp_mask,
 393                         vma, addr, &page_was_allocated);
 394
 395         if (page_was_allocated)
 396                 swap_readpage(retpage);
 397
 398         return retpage;
 399 }
 400
 401 static unsigned long swapin_nr_pages(unsigned long offset)
 402 {
 403         static unsigned long prev_offset;
 404         unsigned int pages, max_pages, last_ra;
 405         static atomic_t last_readahead_pages;
 406
 407         max_pages = 1 << READ_ONCE(page_cluster);
 408         if (max_pages <= 1)
 409                 return 1;
 410
 411         /*
 412          * This heuristic has been found to work well on both sequential and
 413          * random loads, swapping to hard disk or to SSD: please don't ask
 414          * what the "+ 2" means, it just happens to work well, that's all.
 415          */
 416         pages = atomic_xchg(&swapin_readahead_hits, 0) + 2;
 417         if (pages == 2) {
 418                 /*
 419                  * We can have no readahead hits to judge by: but must not get
 420                  * stuck here forever, so check for an adjacent offset instead
 421                  * (and don't even bother to check whether swap type is same).
 422                  */
 423                 if (offset != prev_offset + 1 && offset != prev_offset - 1)
 424                         pages = 1;
 425                 prev_offset = offset;
 426         } else {
 427                 unsigned int roundup = 4;
 428                 while (roundup < pages)
 429                         roundup <<= 1;
 430                 pages = roundup;
 431         }
 432
 433         if (pages > max_pages)
 434                 pages = max_pages;
 435
 436         /* Don't shrink readahead too fast */
 437         last_ra = atomic_read(&last_readahead_pages) / 2;
 438         if (pages < last_ra)
 439                 pages = last_ra;
 440         atomic_set(&last_readahead_pages, pages);
 441
 442         return pages;
 443 }
 444
 445 /**
 446  * swapin_readahead - swap in pages in hope we need them soon
 447  * @entry: swap entry of this memory
 448  * @gfp_mask: memory allocation flags
 449  * @vma: user vma this address belongs to
 450  * @addr: target address for mempolicy
 451  *
 452  * Returns the struct page for entry and addr, after queueing swapin.
 453  *
 454  * Primitive swap readahead code. We simply read an aligned block of
 455  * (1 << page_cluster) entries in the swap area. This method is chosen
 456  * because it doesn't cost us any seek time.  We also make sure to queue
 457  * the 'original' request together with the readahead ones...
 458  *
 459  * This has been extended to use the NUMA policies from the mm triggering
 460  * the readahead.
 461  *
 462  * Caller must hold down_read on the vma->vm_mm if vma is not NULL.
 463  */
 464 struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
 465                         struct vm_area_struct *vma, unsigned long addr)
 466 {
 467         struct page *page;
 468         unsigned long entry_offset = swp_offset(entry);
 469         unsigned long offset = entry_offset;
 470         unsigned long start_offset, end_offset;
 471         unsigned long mask;
 472         struct blk_plug plug;
 473
 474         mask = swapin_nr_pages(offset) - 1;
 475         if (!mask)
 476                 goto skip;
 477
 478         /* Read a page_cluster sized and aligned cluster around offset. */
 479         start_offset = offset & ~mask;
 480         end_offset = offset | mask;
 481         if (!start_offset)      /* First page is swap header. */
 482                 start_offset++;
 483
 484         blk_start_plug(&plug);
 485         for (offset = start_offset; offset <= end_offset ; offset++) {
 486                 /* Ok, do the async read-ahead now */
 487                 page = read_swap_cache_async(swp_entry(swp_type(entry), offset),
 488                                                 gfp_mask, vma, addr);
 489                 if (!page)
 490                         continue;
 491                 if (offset != entry_offset)
 492                         SetPageReadahead(page);
 493                 page_cache_release(page);
 494         }
 495         blk_finish_plug(&plug);
 496
 497         lru_add_drain();        /* Push any new pages onto the LRU now */
 498 skip:
 499         return read_swap_cache_async(entry, gfp_mask, vma, addr);
 500 }