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/swapops.h>
  14 #include <linux/init.h>
  15 #include <linux/pagemap.h>
  16 #include <linux/buffer_head.h>
  17 #include <linux/backing-dev.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, to make sync_page look nicer, and to allow
  26  * future use of radix_tree tags in the swap cache.
  27  */
  28 static const struct address_space_operations swap_aops = {
  29         .writepage      = swap_writepage,
  30         .sync_page      = block_sync_page,
  31         .set_page_dirty = __set_page_dirty_nobuffers,
  32         .migratepage    = migrate_page,
  33 };
  34
  35 static struct backing_dev_info swap_backing_dev_info = {
  36         .capabilities   = BDI_CAP_NO_ACCT_DIRTY | BDI_CAP_NO_WRITEBACK,
  37         .unplug_io_fn   = swap_unplug_io_fn,
  38 };
  39
  40 struct address_space swapper_space = {
  41         .page_tree      = RADIX_TREE_INIT(GFP_ATOMIC|__GFP_NOWARN),
  42         .tree_lock      = __RW_LOCK_UNLOCKED(swapper_space.tree_lock),
  43         .a_ops          = &swap_aops,
  44         .i_mmap_nonlinear = LIST_HEAD_INIT(swapper_space.i_mmap_nonlinear),
  45         .backing_dev_info = &swap_backing_dev_info,
  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         unsigned long noent_race;
  56         unsigned long exist_race;
  57 } swap_cache_info;
  58
  59 void show_swap_cache_info(void)
  60 {
  61         printk("Swap cache: add %lu, delete %lu, find %lu/%lu, race %lu+%lu\n",
  62                 swap_cache_info.add_total, swap_cache_info.del_total,
  63                 swap_cache_info.find_success, swap_cache_info.find_total,
  64                 swap_cache_info.noent_race, swap_cache_info.exist_race);
  65         printk("Free swap  = %lukB\n", nr_swap_pages << (PAGE_SHIFT - 10));
  66         printk("Total swap = %lukB\n", total_swap_pages << (PAGE_SHIFT - 10));
  67 }
  68
  69 /*
  70  * __add_to_swap_cache resembles add_to_page_cache on swapper_space,
  71  * but sets SwapCache flag and private instead of mapping and index.
  72  */
  73 static int __add_to_swap_cache(struct page *page, swp_entry_t entry,
  74                                gfp_t gfp_mask)
  75 {
  76         int error;
  77
  78         BUG_ON(!PageLocked(page));
  79         BUG_ON(PageSwapCache(page));
  80         BUG_ON(PagePrivate(page));
  81         error = radix_tree_preload(gfp_mask);
  82         if (!error) {
  83                 write_lock_irq(&swapper_space.tree_lock);
  84                 error = radix_tree_insert(&swapper_space.page_tree,
  85                                                 entry.val, page);
  86                 if (!error) {
  87                         page_cache_get(page);
  88                         SetPageSwapCache(page);
  89                         set_page_private(page, entry.val);
  90                         total_swapcache_pages++;
  91                         __inc_zone_page_state(page, NR_FILE_PAGES);
  92                 }
  93                 write_unlock_irq(&swapper_space.tree_lock);
  94                 radix_tree_preload_end();
  95         }
  96         return error;
  97 }
  98
  99 static int add_to_swap_cache(struct page *page, swp_entry_t entry)
 100 {
 101         int error;
 102
 103         BUG_ON(PageLocked(page));
 104         if (!swap_duplicate(entry)) {
 105                 INC_CACHE_INFO(noent_race);
 106                 return -ENOENT;
 107         }
 108         SetPageLocked(page);
 109         error = __add_to_swap_cache(page, entry, GFP_KERNEL);
 110         /*
 111          * Anon pages are already on the LRU, we don't run lru_cache_add here.
 112          */
 113         if (error) {
 114                 ClearPageLocked(page);
 115                 swap_free(entry);
 116                 if (error == -EEXIST)
 117                         INC_CACHE_INFO(exist_race);
 118                 return error;
 119         }
 120         INC_CACHE_INFO(add_total);
 121         return 0;
 122 }
 123
 124 /*
 125  * This must be called only on pages that have
 126  * been verified to be in the swap cache.
 127  */
 128 void __delete_from_swap_cache(struct page *page)
 129 {
 130         BUG_ON(!PageLocked(page));
 131         BUG_ON(!PageSwapCache(page));
 132         BUG_ON(PageWriteback(page));
 133         BUG_ON(PagePrivate(page));
 134
 135         radix_tree_delete(&swapper_space.page_tree, page_private(page));
 136         set_page_private(page, 0);
 137         ClearPageSwapCache(page);
 138         total_swapcache_pages--;
 139         __dec_zone_page_state(page, NR_FILE_PAGES);
 140         INC_CACHE_INFO(del_total);
 141 }
 142
 143 /**
 144  * add_to_swap - allocate swap space for a page
 145  * @page: page we want to move to swap
 146  *
 147  * Allocate swap space for the page and add the page to the
 148  * swap cache.  Caller needs to hold the page lock.
 149  */
 150 int add_to_swap(struct page * page, gfp_t gfp_mask)
 151 {
 152         swp_entry_t entry;
 153         int err;
 154
 155         BUG_ON(!PageLocked(page));
 156
 157         for (;;) {
 158                 entry = get_swap_page();
 159                 if (!entry.val)
 160                         return 0;
 161
 162                 /*
 163                  * Radix-tree node allocations from PF_MEMALLOC contexts could
 164                  * completely exhaust the page allocator. __GFP_NOMEMALLOC
 165                  * stops emergency reserves from being allocated.
 166                  *
 167                  * TODO: this could cause a theoretical memory reclaim
 168                  * deadlock in the swap out path.
 169                  */
 170                 /*
 171                  * Add it to the swap cache and mark it dirty
 172                  */
 173                 err = __add_to_swap_cache(page, entry,
 174                                 gfp_mask|__GFP_NOMEMALLOC|__GFP_NOWARN);
 175
 176                 switch (err) {
 177                 case 0:                         /* Success */
 178                         SetPageUptodate(page);
 179                         SetPageDirty(page);
 180                         INC_CACHE_INFO(add_total);
 181                         return 1;
 182                 case -EEXIST:
 183                         /* Raced with "speculative" read_swap_cache_async */
 184                         INC_CACHE_INFO(exist_race);
 185                         swap_free(entry);
 186                         continue;
 187                 default:
 188                         /* -ENOMEM radix-tree allocation failure */
 189                         swap_free(entry);
 190                         return 0;
 191                 }
 192         }
 193 }
 194
 195 /*
 196  * This must be called only on pages that have
 197  * been verified to be in the swap cache and locked.
 198  * It will never put the page into the free list,
 199  * the caller has a reference on the page.
 200  */
 201 void delete_from_swap_cache(struct page *page)
 202 {
 203         swp_entry_t entry;
 204
 205         entry.val = page_private(page);
 206
 207         write_lock_irq(&swapper_space.tree_lock);
 208         __delete_from_swap_cache(page);
 209         write_unlock_irq(&swapper_space.tree_lock);
 210
 211         swap_free(entry);
 212         page_cache_release(page);
 213 }
 214
 215 /*
 216  * Strange swizzling function only for use by shmem_writepage
 217  */
 218 int move_to_swap_cache(struct page *page, swp_entry_t entry)
 219 {
 220         int err = __add_to_swap_cache(page, entry, GFP_ATOMIC);
 221         if (!err) {
 222                 remove_from_page_cache(page);
 223                 page_cache_release(page);       /* pagecache ref */
 224                 if (!swap_duplicate(entry))
 225                         BUG();
 226                 SetPageDirty(page);
 227                 INC_CACHE_INFO(add_total);
 228         } else if (err == -EEXIST)
 229                 INC_CACHE_INFO(exist_race);
 230         return err;
 231 }
 232
 233 /*
 234  * Strange swizzling function for shmem_getpage (and shmem_unuse)
 235  */
 236 int move_from_swap_cache(struct page *page, unsigned long index,
 237                 struct address_space *mapping)
 238 {
 239         int err = add_to_page_cache(page, mapping, index, GFP_ATOMIC);
 240         if (!err) {
 241                 delete_from_swap_cache(page);
 242                 /* shift page from clean_pages to dirty_pages list */
 243                 ClearPageDirty(page);
 244                 set_page_dirty(page);
 245         }
 246         return err;
 247 }
 248
 249 /*
 250  * If we are the only user, then try to free up the swap cache.
 251  *
 252  * Its ok to check for PageSwapCache without the page lock
 253  * here because we are going to recheck again inside
 254  * exclusive_swap_page() _with_ the lock.
 255  *                                      - Marcelo
 256  */
 257 static inline void free_swap_cache(struct page *page)
 258 {
 259         if (PageSwapCache(page) && !TestSetPageLocked(page)) {
 260                 remove_exclusive_swap_page(page);
 261                 unlock_page(page);
 262         }
 263 }
 264
 265 /*
 266  * Perform a free_page(), also freeing any swap cache associated with
 267  * this page if it is the last user of the page.
 268  */
 269 void free_page_and_swap_cache(struct page *page)
 270 {
 271         free_swap_cache(page);
 272         page_cache_release(page);
 273 }
 274
 275 /*
 276  * Passed an array of pages, drop them all from swapcache and then release
 277  * them.  They are removed from the LRU and freed if this is their last use.
 278  */
 279 void free_pages_and_swap_cache(struct page **pages, int nr)
 280 {
 281         struct page **pagep = pages;
 282
 283         lru_add_drain();
 284         while (nr) {
 285                 int todo = min(nr, PAGEVEC_SIZE);
 286                 int i;
 287
 288                 for (i = 0; i < todo; i++)
 289                         free_swap_cache(pagep[i]);
 290                 release_pages(pagep, todo, 0);
 291                 pagep += todo;
 292                 nr -= todo;
 293         }
 294 }
 295
 296 /*
 297  * Lookup a swap entry in the swap cache. A found page will be returned
 298  * unlocked and with its refcount incremented - we rely on the kernel
 299  * lock getting page table operations atomic even if we drop the page
 300  * lock before returning.
 301  */
 302 struct page * lookup_swap_cache(swp_entry_t entry)
 303 {
 304         struct page *page;
 305
 306         page = find_get_page(&swapper_space, entry.val);
 307
 308         if (page)
 309                 INC_CACHE_INFO(find_success);
 310
 311         INC_CACHE_INFO(find_total);
 312         return page;
 313 }
 314
 315 /*
 316  * Locate a page of swap in physical memory, reserving swap cache space
 317  * and reading the disk if it is not already cached.
 318  * A failure return means that either the page allocation failed or that
 319  * the swap entry is no longer in use.
 320  */
 321 struct page *read_swap_cache_async(swp_entry_t entry,
 322                         struct vm_area_struct *vma, unsigned long addr)
 323 {
 324         struct page *found_page, *new_page = NULL;
 325         int err;
 326
 327         do {
 328                 /*
 329                  * First check the swap cache.  Since this is normally
 330                  * called after lookup_swap_cache() failed, re-calling
 331                  * that would confuse statistics.
 332                  */
 333                 found_page = find_get_page(&swapper_space, entry.val);
 334                 if (found_page)
 335                         break;
 336
 337                 /*
 338                  * Get a new page to read into from swap.
 339                  */
 340                 if (!new_page) {
 341                         new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE,
 342                                                                 vma, addr);
 343                         if (!new_page)
 344                                 break;          /* Out of memory */
 345                 }
 346
 347                 /*
 348                  * Associate the page with swap entry in the swap cache.
 349                  * May fail (-ENOENT) if swap entry has been freed since
 350                  * our caller observed it.  May fail (-EEXIST) if there
 351                  * is already a page associated with this entry in the
 352                  * swap cache: added by a racing read_swap_cache_async,
 353                  * or by try_to_swap_out (or shmem_writepage) re-using
 354                  * the just freed swap entry for an existing page.
 355                  * May fail (-ENOMEM) if radix-tree node allocation failed.
 356                  */
 357                 err = add_to_swap_cache(new_page, entry);
 358                 if (!err) {
 359                         /*
 360                          * Initiate read into locked page and return.
 361                          */
 362                         lru_cache_add_active(new_page);
 363                         swap_readpage(NULL, new_page);
 364                         return new_page;
 365                 }
 366         } while (err != -ENOENT && err != -ENOMEM);
 367
 368         if (new_page)
 369                 page_cache_release(new_page);
 370         return found_page;
 371 }
 372
 373 /**
 374  * swapin_readahead - swap in pages in hope we need them soon
 375  * @entry: swap entry of this memory
 376  * @vma: user vma this address belongs to
 377  * @addr: target address for mempolicy
 378  *
 379  * Returns the struct page for entry and addr, after queueing swapin.
 380  *
 381  * Primitive swap readahead code. We simply read an aligned block of
 382  * (1 << page_cluster) entries in the swap area. This method is chosen
 383  * because it doesn't cost us any seek time.  We also make sure to queue
 384  * the 'original' request together with the readahead ones...
 385  *
 386  * This has been extended to use the NUMA policies from the mm triggering
 387  * the readahead.
 388  *
 389  * Caller must hold down_read on the vma->vm_mm if vma is not NULL.
 390  */
 391 struct page *swapin_readahead(swp_entry_t entry,
 392                         struct vm_area_struct *vma, unsigned long addr)
 393 {
 394         int nr_pages;
 395         struct page *page;
 396         unsigned long offset;
 397         unsigned long end_offset;
 398
 399         /*
 400          * Get starting offset for readaround, and number of pages to read.
 401          * Adjust starting address by readbehind (for NUMA interleave case)?
 402          * No, it's very unlikely that swap layout would follow vma layout,
 403          * more likely that neighbouring swap pages came from the same node:
 404          * so use the same "addr" to choose the same node for each swap read.
 405          */
 406         nr_pages = valid_swaphandles(entry, &offset);
 407         for (end_offset = offset + nr_pages; offset < end_offset; offset++) {
 408                 /* Ok, do the async read-ahead now */
 409                 page = read_swap_cache_async(swp_entry(swp_type(entry), offset),
 410                                                 vma, addr);
 411                 if (!page)
 412                         break;
 413                 page_cache_release(page);
 414         }
 415         lru_add_drain();        /* Push any new pages onto the LRU now */
 416         return read_swap_cache_async(entry, vma, addr);
 417 }