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