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 and mark it dirty
 189          */
 190         err = add_to_swap_cache(page, entry,
 191                         __GFP_HIGH|__GFP_NOMEMALLOC|__GFP_NOWARN);
 192
 193         if (!err) {     /* Success */
 194                 SetPageDirty(page);
 195                 return 1;
 196         } else {        /* -ENOMEM radix-tree allocation failure */
 197                 /*
 198                  * add_to_swap_cache() doesn't return -EEXIST, so we can safely
 199                  * clear SWAP_HAS_CACHE flag.
 200                  */
 201                 swapcache_free(entry);
 202                 return 0;
 203         }
 204 }
 205
 206 /*
 207  * This must be called only on pages that have
 208  * been verified to be in the swap cache and locked.
 209  * It will never put the page into the free list,
 210  * the caller has a reference on the page.
 211  */
 212 void delete_from_swap_cache(struct page *page)
 213 {
 214         swp_entry_t entry;
 215         struct address_space *address_space;
 216
 217         entry.val = page_private(page);
 218
 219         address_space = swap_address_space(entry);
 220         spin_lock_irq(&address_space->tree_lock);
 221         __delete_from_swap_cache(page);
 222         spin_unlock_irq(&address_space->tree_lock);
 223
 224         swapcache_free(entry);
 225         page_cache_release(page);
 226 }
 227
 228 /*
 229  * If we are the only user, then try to free up the swap cache.
 230  *
 231  * Its ok to check for PageSwapCache without the page lock
 232  * here because we are going to recheck again inside
 233  * try_to_free_swap() _with_ the lock.
 234  *                                      - Marcelo
 235  */
 236 static inline void free_swap_cache(struct page *page)
 237 {
 238         if (PageSwapCache(page) && !page_mapped(page) && trylock_page(page)) {
 239                 try_to_free_swap(page);
 240                 unlock_page(page);
 241         }
 242 }
 243
 244 /*
 245  * Perform a free_page(), also freeing any swap cache associated with
 246  * this page if it is the last user of the page.
 247  */
 248 void free_page_and_swap_cache(struct page *page)
 249 {
 250         free_swap_cache(page);
 251         page_cache_release(page);
 252 }
 253
 254 /*
 255  * Passed an array of pages, drop them all from swapcache and then release
 256  * them.  They are removed from the LRU and freed if this is their last use.
 257  */
 258 void free_pages_and_swap_cache(struct page **pages, int nr)
 259 {
 260         struct page **pagep = pages;
 261         int i;
 262
 263         lru_add_drain();
 264         for (i = 0; i < nr; i++)
 265                 free_swap_cache(pagep[i]);
 266         release_pages(pagep, nr, false);
 267 }
 268
 269 /*
 270  * Lookup a swap entry in the swap cache. A found page will be returned
 271  * unlocked and with its refcount incremented - we rely on the kernel
 272  * lock getting page table operations atomic even if we drop the page
 273  * lock before returning.
 274  */
 275 struct page * lookup_swap_cache(swp_entry_t entry)
 276 {
 277         struct page *page;
 278
 279         page = find_get_page(swap_address_space(entry), entry.val);
 280
 281         if (page) {
 282                 INC_CACHE_INFO(find_success);
 283                 if (TestClearPageReadahead(page))
 284                         atomic_inc(&swapin_readahead_hits);
 285         }
 286
 287         INC_CACHE_INFO(find_total);
 288         return page;
 289 }
 290
 291 /*
 292  * Locate a page of swap in physical memory, reserving swap cache space
 293  * and reading the disk if it is not already cached.
 294  * A failure return means that either the page allocation failed or that
 295  * the swap entry is no longer in use.
 296  */
 297 struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
 298                         struct vm_area_struct *vma, unsigned long addr)
 299 {
 300         struct page *found_page, *new_page = NULL;
 301         int err;
 302
 303         do {
 304                 /*
 305                  * First check the swap cache.  Since this is normally
 306                  * called after lookup_swap_cache() failed, re-calling
 307                  * that would confuse statistics.
 308                  */
 309                 found_page = find_get_page(swap_address_space(entry),
 310                                         entry.val);
 311                 if (found_page)
 312                         break;
 313
 314                 /*
 315                  * Get a new page to read into from swap.
 316                  */
 317                 if (!new_page) {
 318                         new_page = alloc_page_vma(gfp_mask, vma, addr);
 319                         if (!new_page)
 320                                 break;          /* Out of memory */
 321                 }
 322
 323                 /*
 324                  * call radix_tree_preload() while we can wait.
 325                  */
 326                 err = radix_tree_maybe_preload(gfp_mask & GFP_KERNEL);
 327                 if (err)
 328                         break;
 329
 330                 /*
 331                  * Swap entry may have been freed since our caller observed it.
 332                  */
 333                 err = swapcache_prepare(entry);
 334                 if (err == -EEXIST) {
 335                         radix_tree_preload_end();
 336                         /*
 337                          * We might race against get_swap_page() and stumble
 338                          * across a SWAP_HAS_CACHE swap_map entry whose page
 339                          * has not been brought into the swapcache yet, while
 340                          * the other end is scheduled away waiting on discard
 341                          * I/O completion at scan_swap_map().
 342                          *
 343                          * In order to avoid turning this transitory state
 344                          * into a permanent loop around this -EEXIST case
 345                          * if !CONFIG_PREEMPT and the I/O completion happens
 346                          * to be waiting on the CPU waitqueue where we are now
 347                          * busy looping, we just conditionally invoke the
 348                          * scheduler here, if there are some more important
 349                          * tasks to run.
 350                          */
 351                         cond_resched();
 352                         continue;
 353                 }
 354                 if (err) {              /* swp entry is obsolete ? */
 355                         radix_tree_preload_end();
 356                         break;
 357                 }
 358
 359                 /* May fail (-ENOMEM) if radix-tree node allocation failed. */
 360                 __set_page_locked(new_page);
 361                 SetPageSwapBacked(new_page);
 362                 err = __add_to_swap_cache(new_page, entry);
 363                 if (likely(!err)) {
 364                         radix_tree_preload_end();
 365                         /*
 366                          * Initiate read into locked page and return.
 367                          */
 368                         lru_cache_add_anon(new_page);
 369                         swap_readpage(new_page);
 370                         return new_page;
 371                 }
 372                 radix_tree_preload_end();
 373                 ClearPageSwapBacked(new_page);
 374                 __clear_page_locked(new_page);
 375                 /*
 376                  * add_to_swap_cache() doesn't return -EEXIST, so we can safely
 377                  * clear SWAP_HAS_CACHE flag.
 378                  */
 379                 swapcache_free(entry);
 380         } while (err != -ENOMEM);
 381
 382         if (new_page)
 383                 page_cache_release(new_page);
 384         return found_page;
 385 }
 386
 387 static unsigned long swapin_nr_pages(unsigned long offset)
 388 {
 389         static unsigned long prev_offset;
 390         unsigned int pages, max_pages, last_ra;
 391         static atomic_t last_readahead_pages;
 392
 393         max_pages = 1 << READ_ONCE(page_cluster);
 394         if (max_pages <= 1)
 395                 return 1;
 396
 397         /*
 398          * This heuristic has been found to work well on both sequential and
 399          * random loads, swapping to hard disk or to SSD: please don't ask
 400          * what the "+ 2" means, it just happens to work well, that's all.
 401          */
 402         pages = atomic_xchg(&swapin_readahead_hits, 0) + 2;
 403         if (pages == 2) {
 404                 /*
 405                  * We can have no readahead hits to judge by: but must not get
 406                  * stuck here forever, so check for an adjacent offset instead
 407                  * (and don't even bother to check whether swap type is same).
 408                  */
 409                 if (offset != prev_offset + 1 && offset != prev_offset - 1)
 410                         pages = 1;
 411                 prev_offset = offset;
 412         } else {
 413                 unsigned int roundup = 4;
 414                 while (roundup < pages)
 415                         roundup <<= 1;
 416                 pages = roundup;
 417         }
 418
 419         if (pages > max_pages)
 420                 pages = max_pages;
 421
 422         /* Don't shrink readahead too fast */
 423         last_ra = atomic_read(&last_readahead_pages) / 2;
 424         if (pages < last_ra)
 425                 pages = last_ra;
 426         atomic_set(&last_readahead_pages, pages);
 427
 428         return pages;
 429 }
 430
 431 /**
 432  * swapin_readahead - swap in pages in hope we need them soon
 433  * @entry: swap entry of this memory
 434  * @gfp_mask: memory allocation flags
 435  * @vma: user vma this address belongs to
 436  * @addr: target address for mempolicy
 437  *
 438  * Returns the struct page for entry and addr, after queueing swapin.
 439  *
 440  * Primitive swap readahead code. We simply read an aligned block of
 441  * (1 << page_cluster) entries in the swap area. This method is chosen
 442  * because it doesn't cost us any seek time.  We also make sure to queue
 443  * the 'original' request together with the readahead ones...
 444  *
 445  * This has been extended to use the NUMA policies from the mm triggering
 446  * the readahead.
 447  *
 448  * Caller must hold down_read on the vma->vm_mm if vma is not NULL.
 449  */
 450 struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
 451                         struct vm_area_struct *vma, unsigned long addr)
 452 {
 453         struct page *page;
 454         unsigned long entry_offset = swp_offset(entry);
 455         unsigned long offset = entry_offset;
 456         unsigned long start_offset, end_offset;
 457         unsigned long mask;
 458         struct blk_plug plug;
 459
 460         mask = swapin_nr_pages(offset) - 1;
 461         if (!mask)
 462                 goto skip;
 463
 464         /* Read a page_cluster sized and aligned cluster around offset. */
 465         start_offset = offset & ~mask;
 466         end_offset = offset | mask;
 467         if (!start_offset)      /* First page is swap header. */
 468                 start_offset++;
 469
 470         blk_start_plug(&plug);
 471         for (offset = start_offset; offset <= end_offset ; offset++) {
 472                 /* Ok, do the async read-ahead now */
 473                 page = read_swap_cache_async(swp_entry(swp_type(entry), offset),
 474                                                 gfp_mask, vma, addr);
 475                 if (!page)
 476                         continue;
 477                 if (offset != entry_offset)
 478                         SetPageReadahead(page);
 479                 page_cache_release(page);
 480         }
 481         blk_finish_plug(&plug);
 482
 483         lru_add_drain();        /* Push any new pages onto the LRU now */
 484 skip:
 485         return read_swap_cache_async(entry, gfp_mask, vma, addr);
 486 }