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/module.h>
  10 #include <linux/mm.h>
  11 #include <linux/kernel_stat.h>
  12 #include <linux/swap.h>
  13 #include <linux/init.h>
  14 #include <linux/pagemap.h>
  15 #include <linux/buffer_head.h>
  16 #include <linux/backing-dev.h>
  17 #include <linux/pagevec.h>
  18 #include <linux/migrate.h>
  19
  20 #include <asm/pgtable.h>
  21
  22 /*
  23  * swapper_space is a fiction, retained to simplify the path through
  24  * vmscan's shrink_list, to make sync_page look nicer, and to allow
  25  * future use of radix_tree tags in the swap cache.
  26  */
  27 static const struct address_space_operations swap_aops = {
  28         .writepage      = swap_writepage,
  29         .sync_page      = block_sync_page,
  30         .set_page_dirty = __set_page_dirty_nobuffers,
  31         .migratepage    = migrate_page,
  32 };
  33
  34 static struct backing_dev_info swap_backing_dev_info = {
  35         .capabilities   = BDI_CAP_NO_ACCT_DIRTY | BDI_CAP_NO_WRITEBACK,
  36         .unplug_io_fn   = swap_unplug_io_fn,
  37 };
  38
  39 struct address_space swapper_space = {
  40         .page_tree      = RADIX_TREE_INIT(GFP_ATOMIC|__GFP_NOWARN),
  41         .tree_lock      = __RW_LOCK_UNLOCKED(swapper_space.tree_lock),
  42         .a_ops          = &swap_aops,
  43         .i_mmap_nonlinear = LIST_HEAD_INIT(swapper_space.i_mmap_nonlinear),
  44         .backing_dev_info = &swap_backing_dev_info,
  45 };
  46
  47 #define INC_CACHE_INFO(x)       do { swap_cache_info.x++; } while (0)
  48
  49 static struct {
  50         unsigned long add_total;
  51         unsigned long del_total;
  52         unsigned long find_success;
  53         unsigned long find_total;
  54         unsigned long noent_race;
  55         unsigned long exist_race;
  56 } swap_cache_info;
  57
  58 void show_swap_cache_info(void)
  59 {
  60         printk("Swap cache: add %lu, delete %lu, find %lu/%lu, race %lu+%lu\n",
  61                 swap_cache_info.add_total, swap_cache_info.del_total,
  62                 swap_cache_info.find_success, swap_cache_info.find_total,
  63                 swap_cache_info.noent_race, swap_cache_info.exist_race);
  64         printk("Free swap  = %lukB\n", nr_swap_pages << (PAGE_SHIFT - 10));
  65         printk("Total swap = %lukB\n", total_swap_pages << (PAGE_SHIFT - 10));
  66 }
  67
  68 /*
  69  * __add_to_swap_cache resembles add_to_page_cache on swapper_space,
  70  * but sets SwapCache flag and private instead of mapping and index.
  71  */
  72 static int __add_to_swap_cache(struct page *page, swp_entry_t entry,
  73                                gfp_t gfp_mask)
  74 {
  75         int error;
  76
  77         BUG_ON(PageSwapCache(page));
  78         BUG_ON(PagePrivate(page));
  79         error = radix_tree_preload(gfp_mask);
  80         if (!error) {
  81                 write_lock_irq(&swapper_space.tree_lock);
  82                 error = radix_tree_insert(&swapper_space.page_tree,
  83                                                 entry.val, page);
  84                 if (!error) {
  85                         page_cache_get(page);
  86                         SetPageLocked(page);
  87                         SetPageSwapCache(page);
  88                         set_page_private(page, entry.val);
  89                         total_swapcache_pages++;
  90                         __inc_zone_page_state(page, NR_FILE_PAGES);
  91                 }
  92                 write_unlock_irq(&swapper_space.tree_lock);
  93                 radix_tree_preload_end();
  94         }
  95         return error;
  96 }
  97
  98 static int add_to_swap_cache(struct page *page, swp_entry_t entry)
  99 {
 100         int error;
 101
 102         if (!swap_duplicate(entry)) {
 103                 INC_CACHE_INFO(noent_race);
 104                 return -ENOENT;
 105         }
 106         error = __add_to_swap_cache(page, entry, GFP_KERNEL);
 107         /*
 108          * Anon pages are already on the LRU, we don't run lru_cache_add here.
 109          */
 110         if (error) {
 111                 swap_free(entry);
 112                 if (error == -EEXIST)
 113                         INC_CACHE_INFO(exist_race);
 114                 return error;
 115         }
 116         INC_CACHE_INFO(add_total);
 117         return 0;
 118 }
 119
 120 /*
 121  * This must be called only on pages that have
 122  * been verified to be in the swap cache.
 123  */
 124 void __delete_from_swap_cache(struct page *page)
 125 {
 126         BUG_ON(!PageLocked(page));
 127         BUG_ON(!PageSwapCache(page));
 128         BUG_ON(PageWriteback(page));
 129         BUG_ON(PagePrivate(page));
 130
 131         radix_tree_delete(&swapper_space.page_tree, page_private(page));
 132         set_page_private(page, 0);
 133         ClearPageSwapCache(page);
 134         total_swapcache_pages--;
 135         __dec_zone_page_state(page, NR_FILE_PAGES);
 136         INC_CACHE_INFO(del_total);
 137 }
 138
 139 /**
 140  * add_to_swap - allocate swap space for a page
 141  * @page: page we want to move to swap
 142  *
 143  * Allocate swap space for the page and add the page to the
 144  * swap cache.  Caller needs to hold the page lock.
 145  */
 146 int add_to_swap(struct page * page, gfp_t gfp_mask)
 147 {
 148         swp_entry_t entry;
 149         int err;
 150
 151         BUG_ON(!PageLocked(page));
 152
 153         for (;;) {
 154                 entry = get_swap_page();
 155                 if (!entry.val)
 156                         return 0;
 157
 158                 /*
 159                  * Radix-tree node allocations from PF_MEMALLOC contexts could
 160                  * completely exhaust the page allocator. __GFP_NOMEMALLOC
 161                  * stops emergency reserves from being allocated.
 162                  *
 163                  * TODO: this could cause a theoretical memory reclaim
 164                  * deadlock in the swap out path.
 165                  */
 166                 /*
 167                  * Add it to the swap cache and mark it dirty
 168                  */
 169                 err = __add_to_swap_cache(page, entry,
 170                                 gfp_mask|__GFP_NOMEMALLOC|__GFP_NOWARN);
 171
 172                 switch (err) {
 173                 case 0:                         /* Success */
 174                         SetPageUptodate(page);
 175                         SetPageDirty(page);
 176                         INC_CACHE_INFO(add_total);
 177                         return 1;
 178                 case -EEXIST:
 179                         /* Raced with "speculative" read_swap_cache_async */
 180                         INC_CACHE_INFO(exist_race);
 181                         swap_free(entry);
 182                         continue;
 183                 default:
 184                         /* -ENOMEM radix-tree allocation failure */
 185                         swap_free(entry);
 186                         return 0;
 187                 }
 188         }
 189 }
 190
 191 /*
 192  * This must be called only on pages that have
 193  * been verified to be in the swap cache and locked.
 194  * It will never put the page into the free list,
 195  * the caller has a reference on the page.
 196  */
 197 void delete_from_swap_cache(struct page *page)
 198 {
 199         swp_entry_t entry;
 200
 201         entry.val = page_private(page);
 202
 203         write_lock_irq(&swapper_space.tree_lock);
 204         __delete_from_swap_cache(page);
 205         write_unlock_irq(&swapper_space.tree_lock);
 206
 207         swap_free(entry);
 208         page_cache_release(page);
 209 }
 210
 211 /*
 212  * Strange swizzling function only for use by shmem_writepage
 213  */
 214 int move_to_swap_cache(struct page *page, swp_entry_t entry)
 215 {
 216         int err = __add_to_swap_cache(page, entry, GFP_ATOMIC);
 217         if (!err) {
 218                 remove_from_page_cache(page);
 219                 page_cache_release(page);       /* pagecache ref */
 220                 if (!swap_duplicate(entry))
 221                         BUG();
 222                 SetPageDirty(page);
 223                 INC_CACHE_INFO(add_total);
 224         } else if (err == -EEXIST)
 225                 INC_CACHE_INFO(exist_race);
 226         return err;
 227 }
 228
 229 /*
 230  * Strange swizzling function for shmem_getpage (and shmem_unuse)
 231  */
 232 int move_from_swap_cache(struct page *page, unsigned long index,
 233                 struct address_space *mapping)
 234 {
 235         int err = add_to_page_cache(page, mapping, index, GFP_ATOMIC);
 236         if (!err) {
 237                 delete_from_swap_cache(page);
 238                 /* shift page from clean_pages to dirty_pages list */
 239                 ClearPageDirty(page);
 240                 set_page_dirty(page);
 241         }
 242         return err;
 243 }
 244
 245 /*
 246  * If we are the only user, then try to free up the swap cache.
 247  *
 248  * Its ok to check for PageSwapCache without the page lock
 249  * here because we are going to recheck again inside
 250  * exclusive_swap_page() _with_ the lock.
 251  *                                      - Marcelo
 252  */
 253 static inline void free_swap_cache(struct page *page)
 254 {
 255         if (PageSwapCache(page) && !TestSetPageLocked(page)) {
 256                 remove_exclusive_swap_page(page);
 257                 unlock_page(page);
 258         }
 259 }
 260
 261 /*
 262  * Perform a free_page(), also freeing any swap cache associated with
 263  * this page if it is the last user of the page.
 264  */
 265 void free_page_and_swap_cache(struct page *page)
 266 {
 267         free_swap_cache(page);
 268         page_cache_release(page);
 269 }
 270
 271 /*
 272  * Passed an array of pages, drop them all from swapcache and then release
 273  * them.  They are removed from the LRU and freed if this is their last use.
 274  */
 275 void free_pages_and_swap_cache(struct page **pages, int nr)
 276 {
 277         struct page **pagep = pages;
 278
 279         lru_add_drain();
 280         while (nr) {
 281                 int todo = min(nr, PAGEVEC_SIZE);
 282                 int i;
 283
 284                 for (i = 0; i < todo; i++)
 285                         free_swap_cache(pagep[i]);
 286                 release_pages(pagep, todo, 0);
 287                 pagep += todo;
 288                 nr -= todo;
 289         }
 290 }
 291
 292 /*
 293  * Lookup a swap entry in the swap cache. A found page will be returned
 294  * unlocked and with its refcount incremented - we rely on the kernel
 295  * lock getting page table operations atomic even if we drop the page
 296  * lock before returning.
 297  */
 298 struct page * lookup_swap_cache(swp_entry_t entry)
 299 {
 300         struct page *page;
 301
 302         page = find_get_page(&swapper_space, entry.val);
 303
 304         if (page)
 305                 INC_CACHE_INFO(find_success);
 306
 307         INC_CACHE_INFO(find_total);
 308         return page;
 309 }
 310
 311 /*
 312  * Locate a page of swap in physical memory, reserving swap cache space
 313  * and reading the disk if it is not already cached.
 314  * A failure return means that either the page allocation failed or that
 315  * the swap entry is no longer in use.
 316  */
 317 struct page *read_swap_cache_async(swp_entry_t entry,
 318                         struct vm_area_struct *vma, unsigned long addr)
 319 {
 320         struct page *found_page, *new_page = NULL;
 321         int err;
 322
 323         do {
 324                 /*
 325                  * First check the swap cache.  Since this is normally
 326                  * called after lookup_swap_cache() failed, re-calling
 327                  * that would confuse statistics.
 328                  */
 329                 found_page = find_get_page(&swapper_space, entry.val);
 330                 if (found_page)
 331                         break;
 332
 333                 /*
 334                  * Get a new page to read into from swap.
 335                  */
 336                 if (!new_page) {
 337                         new_page = alloc_page_vma(GFP_HIGHUSER, vma, addr);
 338                         if (!new_page)
 339                                 break;          /* Out of memory */
 340                 }
 341
 342                 /*
 343                  * Associate the page with swap entry in the swap cache.
 344                  * May fail (-ENOENT) if swap entry has been freed since
 345                  * our caller observed it.  May fail (-EEXIST) if there
 346                  * is already a page associated with this entry in the
 347                  * swap cache: added by a racing read_swap_cache_async,
 348                  * or by try_to_swap_out (or shmem_writepage) re-using
 349                  * the just freed swap entry for an existing page.
 350                  * May fail (-ENOMEM) if radix-tree node allocation failed.
 351                  */
 352                 err = add_to_swap_cache(new_page, entry);
 353                 if (!err) {
 354                         /*
 355                          * Initiate read into locked page and return.
 356                          */
 357                         lru_cache_add_active(new_page);
 358                         swap_readpage(NULL, new_page);
 359                         return new_page;
 360                 }
 361         } while (err != -ENOENT && err != -ENOMEM);
 362
 363         if (new_page)
 364                 page_cache_release(new_page);
 365         return found_page;
 366 }