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 #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, to make sync_page look nicer, and to allow
  27  * future use of radix_tree tags in the swap cache.
  28  */
  29 static const struct address_space_operations swap_aops = {
  30         .writepage      = swap_writepage,
  31         .sync_page      = block_sync_page,
  32         .set_page_dirty = __set_page_dirty_nobuffers,
  33         .migratepage    = migrate_page,
  34 };
  35
  36 static struct backing_dev_info swap_backing_dev_info = {
  37         .name           = "swap",
  38         .capabilities   = BDI_CAP_NO_ACCT_AND_WRITEBACK | BDI_CAP_SWAP_BACKED,
  39         .unplug_io_fn   = swap_unplug_io_fn,
  40 };
  41
  42 struct address_space swapper_space = {
  43         .page_tree      = RADIX_TREE_INIT(GFP_ATOMIC|__GFP_NOWARN),
  44         .tree_lock      = __SPIN_LOCK_UNLOCKED(swapper_space.tree_lock),
  45         .a_ops          = &swap_aops,
  46         .i_mmap_nonlinear = LIST_HEAD_INIT(swapper_space.i_mmap_nonlinear),
  47         .backing_dev_info = &swap_backing_dev_info,
  48 };
  49
  50 #define INC_CACHE_INFO(x)       do { swap_cache_info.x++; } while (0)
  51
  52 static struct {
  53         unsigned long add_total;
  54         unsigned long del_total;
  55         unsigned long find_success;
  56         unsigned long find_total;
  57 } swap_cache_info;
  58
  59 void show_swap_cache_info(void)
  60 {
  61         printk("%lu pages in swap cache\n", total_swapcache_pages);
  62         printk("Swap cache stats: add %lu, delete %lu, find %lu/%lu\n",
  63                 swap_cache_info.add_total, swap_cache_info.del_total,
  64                 swap_cache_info.find_success, swap_cache_info.find_total);
  65         printk("Free swap  = %ldkB\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_locked 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 {
  75         int error;
  76
  77         VM_BUG_ON(!PageLocked(page));
  78         VM_BUG_ON(PageSwapCache(page));
  79         VM_BUG_ON(!PageSwapBacked(page));
  80
  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, entry.val, page);
  87         if (likely(!error)) {
  88                 total_swapcache_pages++;
  89                 __inc_zone_page_state(page, NR_FILE_PAGES);
  90                 INC_CACHE_INFO(add_total);
  91         }
  92         spin_unlock_irq(&swapper_space.tree_lock);
  93
  94         if (unlikely(error)) {
  95                 /*
  96                  * Only the context which have set SWAP_HAS_CACHE flag
  97                  * would call add_to_swap_cache().
  98                  * So add_to_swap_cache() doesn't returns -EEXIST.
  99                  */
 100                 VM_BUG_ON(error == -EEXIST);
 101                 set_page_private(page, 0UL);
 102                 ClearPageSwapCache(page);
 103                 page_cache_release(page);
 104         }
 105
 106         return error;
 107 }
 108
 109
 110 int add_to_swap_cache(struct page *page, swp_entry_t entry, gfp_t gfp_mask)
 111 {
 112         int error;
 113
 114         error = radix_tree_preload(gfp_mask);
 115         if (!error) {
 116                 error = __add_to_swap_cache(page, entry);
 117                 radix_tree_preload_end();
 118         }
 119         return error;
 120 }
 121
 122 /*
 123  * This must be called only on pages that have
 124  * been verified to be in the swap cache.
 125  */
 126 void __delete_from_swap_cache(struct page *page)
 127 {
 128         VM_BUG_ON(!PageLocked(page));
 129         VM_BUG_ON(!PageSwapCache(page));
 130         VM_BUG_ON(PageWriteback(page));
 131
 132         radix_tree_delete(&swapper_space.page_tree, page_private(page));
 133         set_page_private(page, 0);
 134         ClearPageSwapCache(page);
 135         total_swapcache_pages--;
 136         __dec_zone_page_state(page, NR_FILE_PAGES);
 137         INC_CACHE_INFO(del_total);
 138 }
 139
 140 /**
 141  * add_to_swap - allocate swap space for a page
 142  * @page: page we want to move to swap
 143  *
 144  * Allocate swap space for the page and add the page to the
 145  * swap cache.  Caller needs to hold the page lock.
 146  */
 147 int add_to_swap(struct page *page)
 148 {
 149         swp_entry_t entry;
 150         int err;
 151
 152         VM_BUG_ON(!PageLocked(page));
 153         VM_BUG_ON(!PageUptodate(page));
 154
 155         entry = get_swap_page();
 156         if (!entry.val)
 157                 return 0;
 158
 159         /*
 160          * Radix-tree node allocations from PF_MEMALLOC contexts could
 161          * completely exhaust the page allocator. __GFP_NOMEMALLOC
 162          * stops emergency reserves from being allocated.
 163          *
 164          * TODO: this could cause a theoretical memory reclaim
 165          * deadlock in the swap out path.
 166          */
 167         /*
 168          * Add it to the swap cache and mark it dirty
 169          */
 170         err = add_to_swap_cache(page, entry,
 171                         __GFP_HIGH|__GFP_NOMEMALLOC|__GFP_NOWARN);
 172
 173         if (!err) {     /* Success */
 174                 SetPageDirty(page);
 175                 return 1;
 176         } else {        /* -ENOMEM radix-tree allocation failure */
 177                 /*
 178                  * add_to_swap_cache() doesn't return -EEXIST, so we can safely
 179                  * clear SWAP_HAS_CACHE flag.
 180                  */
 181                 swapcache_free(entry, NULL);
 182                 return 0;
 183         }
 184 }
 185
 186 /*
 187  * This must be called only on pages that have
 188  * been verified to be in the swap cache and locked.
 189  * It will never put the page into the free list,
 190  * the caller has a reference on the page.
 191  */
 192 void delete_from_swap_cache(struct page *page)
 193 {
 194         swp_entry_t entry;
 195
 196         entry.val = page_private(page);
 197
 198         spin_lock_irq(&swapper_space.tree_lock);
 199         __delete_from_swap_cache(page);
 200         spin_unlock_irq(&swapper_space.tree_lock);
 201
 202         swapcache_free(entry, page);
 203         page_cache_release(page);
 204 }
 205
 206 /*
 207  * If we are the only user, then try to free up the swap cache.
 208  *
 209  * Its ok to check for PageSwapCache without the page lock
 210  * here because we are going to recheck again inside
 211  * try_to_free_swap() _with_ the lock.
 212  *                                      - Marcelo
 213  */
 214 static inline void free_swap_cache(struct page *page)
 215 {
 216         if (PageSwapCache(page) && !page_mapped(page) && trylock_page(page)) {
 217                 try_to_free_swap(page);
 218                 unlock_page(page);
 219         }
 220 }
 221
 222 /*
 223  * Perform a free_page(), also freeing any swap cache associated with
 224  * this page if it is the last user of the page.
 225  */
 226 void free_page_and_swap_cache(struct page *page)
 227 {
 228         free_swap_cache(page);
 229         page_cache_release(page);
 230 }
 231
 232 /*
 233  * Passed an array of pages, drop them all from swapcache and then release
 234  * them.  They are removed from the LRU and freed if this is their last use.
 235  */
 236 void free_pages_and_swap_cache(struct page **pages, int nr)
 237 {
 238         struct page **pagep = pages;
 239
 240         lru_add_drain();
 241         while (nr) {
 242                 int todo = min(nr, PAGEVEC_SIZE);
 243                 int i;
 244
 245                 for (i = 0; i < todo; i++)
 246                         free_swap_cache(pagep[i]);
 247                 release_pages(pagep, todo, 0);
 248                 pagep += todo;
 249                 nr -= todo;
 250         }
 251 }
 252
 253 /*
 254  * Lookup a swap entry in the swap cache. A found page will be returned
 255  * unlocked and with its refcount incremented - we rely on the kernel
 256  * lock getting page table operations atomic even if we drop the page
 257  * lock before returning.
 258  */
 259 struct page * lookup_swap_cache(swp_entry_t entry)
 260 {
 261         struct page *page;
 262
 263         page = find_get_page(&swapper_space, entry.val);
 264
 265         if (page)
 266                 INC_CACHE_INFO(find_success);
 267
 268         INC_CACHE_INFO(find_total);
 269         return page;
 270 }
 271
 272 /*
 273  * Locate a page of swap in physical memory, reserving swap cache space
 274  * and reading the disk if it is not already cached.
 275  * A failure return means that either the page allocation failed or that
 276  * the swap entry is no longer in use.
 277  */
 278 struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
 279                         struct vm_area_struct *vma, unsigned long addr)
 280 {
 281         struct page *found_page, *new_page = NULL;
 282         int err;
 283
 284         do {
 285                 /*
 286                  * First check the swap cache.  Since this is normally
 287                  * called after lookup_swap_cache() failed, re-calling
 288                  * that would confuse statistics.
 289                  */
 290                 found_page = find_get_page(&swapper_space, entry.val);
 291                 if (found_page)
 292                         break;
 293
 294                 /*
 295                  * Get a new page to read into from swap.
 296                  */
 297                 if (!new_page) {
 298                         new_page = alloc_page_vma(gfp_mask, vma, addr);
 299                         if (!new_page)
 300                                 break;          /* Out of memory */
 301                 }
 302
 303                 /*
 304                  * call radix_tree_preload() while we can wait.
 305                  */
 306                 err = radix_tree_preload(gfp_mask & GFP_KERNEL);
 307                 if (err)
 308                         break;
 309
 310                 /*
 311                  * Swap entry may have been freed since our caller observed it.
 312                  */
 313                 err = swapcache_prepare(entry);
 314                 if (err == -EEXIST) {   /* seems racy */
 315                         radix_tree_preload_end();
 316                         continue;
 317                 }
 318                 if (err) {              /* swp entry is obsolete ? */
 319                         radix_tree_preload_end();
 320                         break;
 321                 }
 322
 323                 /* May fail (-ENOMEM) if radix-tree node allocation failed. */
 324                 __set_page_locked(new_page);
 325                 SetPageSwapBacked(new_page);
 326                 err = __add_to_swap_cache(new_page, entry);
 327                 if (likely(!err)) {
 328                         radix_tree_preload_end();
 329                         /*
 330                          * Initiate read into locked page and return.
 331                          */
 332                         lru_cache_add_anon(new_page);
 333                         swap_readpage(new_page);
 334                         return new_page;
 335                 }
 336                 radix_tree_preload_end();
 337                 ClearPageSwapBacked(new_page);
 338                 __clear_page_locked(new_page);
 339                 /*
 340                  * add_to_swap_cache() doesn't return -EEXIST, so we can safely
 341                  * clear SWAP_HAS_CACHE flag.
 342                  */
 343                 swapcache_free(entry, NULL);
 344         } while (err != -ENOMEM);
 345
 346         if (new_page)
 347                 page_cache_release(new_page);
 348         return found_page;
 349 }
 350
 351 /**
 352  * swapin_readahead - swap in pages in hope we need them soon
 353  * @entry: swap entry of this memory
 354  * @gfp_mask: memory allocation flags
 355  * @vma: user vma this address belongs to
 356  * @addr: target address for mempolicy
 357  *
 358  * Returns the struct page for entry and addr, after queueing swapin.
 359  *
 360  * Primitive swap readahead code. We simply read an aligned block of
 361  * (1 << page_cluster) entries in the swap area. This method is chosen
 362  * because it doesn't cost us any seek time.  We also make sure to queue
 363  * the 'original' request together with the readahead ones...
 364  *
 365  * This has been extended to use the NUMA policies from the mm triggering
 366  * the readahead.
 367  *
 368  * Caller must hold down_read on the vma->vm_mm if vma is not NULL.
 369  */
 370 struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
 371                         struct vm_area_struct *vma, unsigned long addr)
 372 {
 373         int nr_pages;
 374         struct page *page;
 375         unsigned long offset;
 376         unsigned long end_offset;
 377
 378         /*
 379          * Get starting offset for readaround, and number of pages to read.
 380          * Adjust starting address by readbehind (for NUMA interleave case)?
 381          * No, it's very unlikely that swap layout would follow vma layout,
 382          * more likely that neighbouring swap pages came from the same node:
 383          * so use the same "addr" to choose the same node for each swap read.
 384          */
 385         nr_pages = valid_swaphandles(entry, &offset);
 386         for (end_offset = offset + nr_pages; offset < end_offset; offset++) {
 387                 /* Ok, do the async read-ahead now */
 388                 page = read_swap_cache_async(swp_entry(swp_type(entry), offset),
 389                                                 gfp_mask, vma, addr);
 390                 if (!page)
 391                         break;
 392                 page_cache_release(page);
 393         }
 394         lru_add_drain();        /* Push any new pages onto the LRU now */
 395         return read_swap_cache_async(entry, gfp_mask, vma, addr);
 396 }