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