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