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