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/gfp.h>
  12 #include <linux/kernel_stat.h>
  13 #include <linux/swap.h>
  14 #include <linux/swapops.h>
  15 #include <linux/init.h>
  16 #include <linux/pagemap.h>
  17 #include <linux/buffer_head.h>
  18 #include <linux/backing-dev.h>
  19 #include <linux/pagevec.h>
  20 #include <linux/migrate.h>
  21 #include <linux/page_cgroup.h>
  22
  23 #include <asm/pgtable.h>
  24
  25 /*
  26  * swapper_space is a fiction, retained to simplify the path through
  27  * vmscan's shrink_page_list, to make sync_page look nicer, and to allow
  28  * future use of radix_tree tags in the swap cache.
  29  */
  30 static const struct address_space_operations swap_aops = {
  31         .writepage      = swap_writepage,
  32         .sync_page      = block_sync_page,
  33         .set_page_dirty = __set_page_dirty_nobuffers,
  34         .migratepage    = migrate_page,
  35 };
  36
  37 static struct backing_dev_info swap_backing_dev_info = {
  38         .name           = "swap",
  39         .capabilities   = BDI_CAP_NO_ACCT_AND_WRITEBACK | BDI_CAP_SWAP_BACKED,
  40         .unplug_io_fn   = swap_unplug_io_fn,
  41 };
  42
  43 struct address_space swapper_space = {
  44         .page_tree      = RADIX_TREE_INIT(GFP_ATOMIC|__GFP_NOWARN),
  45         .tree_lock      = __SPIN_LOCK_UNLOCKED(swapper_space.tree_lock),
  46         .a_ops          = &swap_aops,
  47         .i_mmap_nonlinear = LIST_HEAD_INIT(swapper_space.i_mmap_nonlinear),
  48         .backing_dev_info = &swap_backing_dev_info,
  49 };
  50
  51 #define INC_CACHE_INFO(x)       do { swap_cache_info.x++; } while (0)
  52
  53 static struct {
  54         unsigned long add_total;
  55         unsigned long del_total;
  56         unsigned long find_success;
  57         unsigned long find_total;
  58 } swap_cache_info;
  59
  60 void show_swap_cache_info(void)
  61 {
  62         printk("%lu pages in swap cache\n", total_swapcache_pages);
  63         printk("Swap cache stats: add %lu, delete %lu, find %lu/%lu\n",
  64                 swap_cache_info.add_total, swap_cache_info.del_total,
  65                 swap_cache_info.find_success, swap_cache_info.find_total);
  66         printk("Free swap  = %ldkB\n", nr_swap_pages << (PAGE_SHIFT - 10));
  67         printk("Total swap = %lukB\n", total_swap_pages << (PAGE_SHIFT - 10));
  68 }
  69
  70 /*
  71  * __add_to_swap_cache resembles add_to_page_cache_locked on swapper_space,
  72  * but sets SwapCache flag and private instead of mapping and index.
  73  */
  74 static int __add_to_swap_cache(struct page *page, swp_entry_t entry)
  75 {
  76         int error;
  77
  78         VM_BUG_ON(!PageLocked(page));
  79         VM_BUG_ON(PageSwapCache(page));
  80         VM_BUG_ON(!PageSwapBacked(page));
  81
  82         page_cache_get(page);
  83         SetPageSwapCache(page);
  84         set_page_private(page, entry.val);
  85
  86         spin_lock_irq(&swapper_space.tree_lock);
  87         error = radix_tree_insert(&swapper_space.page_tree, 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
  95         if (unlikely(error)) {
  96                 /*
  97                  * Only the context which have set SWAP_HAS_CACHE flag
  98                  * would call add_to_swap_cache().
  99                  * So add_to_swap_cache() doesn't returns -EEXIST.
 100                  */
 101                 VM_BUG_ON(error == -EEXIST);
 102                 set_page_private(page, 0UL);
 103                 ClearPageSwapCache(page);
 104                 page_cache_release(page);
 105         }
 106
 107         return error;
 108 }
 109
 110
 111 int add_to_swap_cache(struct page *page, swp_entry_t entry, gfp_t gfp_mask)
 112 {
 113         int error;
 114
 115         error = radix_tree_preload(gfp_mask);
 116         if (!error) {
 117                 error = __add_to_swap_cache(page, entry);
 118                 radix_tree_preload_end();
 119         }
 120         return error;
 121 }
 122
 123 /*
 124  * This must be called only on pages that have
 125  * been verified to be in the swap cache.
 126  */
 127 void __delete_from_swap_cache(struct page *page)
 128 {
 129         VM_BUG_ON(!PageLocked(page));
 130         VM_BUG_ON(!PageSwapCache(page));
 131         VM_BUG_ON(PageWriteback(page));
 132
 133         radix_tree_delete(&swapper_space.page_tree, page_private(page));
 134         set_page_private(page, 0);
 135         ClearPageSwapCache(page);
 136         total_swapcache_pages--;
 137         __dec_zone_page_state(page, NR_FILE_PAGES);
 138         INC_CACHE_INFO(del_total);
 139 }
 140
 141 /**
 142  * add_to_swap - allocate swap space for a page
 143  * @page: page we want to move to swap
 144  *
 145  * Allocate swap space for the page and add the page to the
 146  * swap cache.  Caller needs to hold the page lock.
 147  */
 148 int add_to_swap(struct page *page)
 149 {
 150         swp_entry_t entry;
 151         int err;
 152
 153         VM_BUG_ON(!PageLocked(page));
 154         VM_BUG_ON(!PageUptodate(page));
 155
 156         entry = get_swap_page();
 157         if (!entry.val)
 158                 return 0;
 159
 160         /*
 161          * Radix-tree node allocations from PF_MEMALLOC contexts could
 162          * completely exhaust the page allocator. __GFP_NOMEMALLOC
 163          * stops emergency reserves from being allocated.
 164          *
 165          * TODO: this could cause a theoretical memory reclaim
 166          * deadlock in the swap out path.
 167          */
 168         /*
 169          * Add it to the swap cache and mark it dirty
 170          */
 171         err = add_to_swap_cache(page, entry,
 172                         __GFP_HIGH|__GFP_NOMEMALLOC|__GFP_NOWARN);
 173
 174         if (!err) {     /* Success */
 175                 SetPageDirty(page);
 176                 return 1;
 177         } else {        /* -ENOMEM radix-tree allocation failure */
 178                 /*
 179                  * add_to_swap_cache() doesn't return -EEXIST, so we can safely
 180                  * clear SWAP_HAS_CACHE flag.
 181                  */
 182                 swapcache_free(entry, NULL);
 183                 return 0;
 184         }
 185 }
 186
 187 /*
 188  * This must be called only on pages that have
 189  * been verified to be in the swap cache and locked.
 190  * It will never put the page into the free list,
 191  * the caller has a reference on the page.
 192  */
 193 void delete_from_swap_cache(struct page *page)
 194 {
 195         swp_entry_t entry;
 196
 197         entry.val = page_private(page);
 198
 199         spin_lock_irq(&swapper_space.tree_lock);
 200         __delete_from_swap_cache(page);
 201         spin_unlock_irq(&swapper_space.tree_lock);
 202
 203         swapcache_free(entry, page);
 204         page_cache_release(page);
 205 }
 206
 207 /*
 208  * If we are the only user, then try to free up the swap cache.
 209  *
 210  * Its ok to check for PageSwapCache without the page lock
 211  * here because we are going to recheck again inside
 212  * try_to_free_swap() _with_ the lock.
 213  *                                      - Marcelo
 214  */
 215 static inline void free_swap_cache(struct page *page)
 216 {
 217         if (PageSwapCache(page) && !page_mapped(page) && trylock_page(page)) {
 218                 try_to_free_swap(page);
 219                 unlock_page(page);
 220         }
 221 }
 222
 223 /*
 224  * Perform a free_page(), also freeing any swap cache associated with
 225  * this page if it is the last user of the page.
 226  */
 227 void free_page_and_swap_cache(struct page *page)
 228 {
 229         free_swap_cache(page);
 230         page_cache_release(page);
 231 }
 232
 233 /*
 234  * Passed an array of pages, drop them all from swapcache and then release
 235  * them.  They are removed from the LRU and freed if this is their last use.
 236  */
 237 void free_pages_and_swap_cache(struct page **pages, int nr)
 238 {
 239         struct page **pagep = pages;
 240
 241         lru_add_drain();
 242         while (nr) {
 243                 int todo = min(nr, PAGEVEC_SIZE);
 244                 int i;
 245
 246                 for (i = 0; i < todo; i++)
 247                         free_swap_cache(pagep[i]);
 248                 release_pages(pagep, todo, 0);
 249                 pagep += todo;
 250                 nr -= todo;
 251         }
 252 }
 253
 254 /*
 255  * Lookup a swap entry in the swap cache. A found page will be returned
 256  * unlocked and with its refcount incremented - we rely on the kernel
 257  * lock getting page table operations atomic even if we drop the page
 258  * lock before returning.
 259  */
 260 struct page * lookup_swap_cache(swp_entry_t entry)
 261 {
 262         struct page *page;
 263
 264         page = find_get_page(&swapper_space, entry.val);
 265
 266         if (page)
 267                 INC_CACHE_INFO(find_success);
 268
 269         INC_CACHE_INFO(find_total);
 270         return page;
 271 }
 272
 273 /*
 274  * Locate a page of swap in physical memory, reserving swap cache space
 275  * and reading the disk if it is not already cached.
 276  * A failure return means that either the page allocation failed or that
 277  * the swap entry is no longer in use.
 278  */
 279 struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
 280                         struct vm_area_struct *vma, unsigned long addr)
 281 {
 282         struct page *found_page, *new_page = NULL;
 283         int err;
 284
 285         do {
 286                 /*
 287                  * First check the swap cache.  Since this is normally
 288                  * called after lookup_swap_cache() failed, re-calling
 289                  * that would confuse statistics.
 290                  */
 291                 found_page = find_get_page(&swapper_space, entry.val);
 292                 if (found_page)
 293                         break;
 294
 295                 /*
 296                  * Get a new page to read into from swap.
 297                  */
 298                 if (!new_page) {
 299                         new_page = alloc_page_vma(gfp_mask, vma, addr);
 300                         if (!new_page)
 301                                 break;          /* Out of memory */
 302                 }
 303
 304                 /*
 305                  * call radix_tree_preload() while we can wait.
 306                  */
 307                 err = radix_tree_preload(gfp_mask & GFP_KERNEL);
 308                 if (err)
 309                         break;
 310
 311                 /*
 312                  * Swap entry may have been freed since our caller observed it.
 313                  */
 314                 err = swapcache_prepare(entry);
 315                 if (err == -EEXIST) {   /* seems racy */
 316                         radix_tree_preload_end();
 317                         continue;
 318                 }
 319                 if (err) {              /* swp entry is obsolete ? */
 320                         radix_tree_preload_end();
 321                         break;
 322                 }
 323
 324                 /* May fail (-ENOMEM) if radix-tree node allocation failed. */
 325                 __set_page_locked(new_page);
 326                 SetPageSwapBacked(new_page);
 327                 err = __add_to_swap_cache(new_page, entry);
 328                 if (likely(!err)) {
 329                         radix_tree_preload_end();
 330                         /*
 331                          * Initiate read into locked page and return.
 332                          */
 333                         lru_cache_add_anon(new_page);
 334                         swap_readpage(new_page);
 335                         return new_page;
 336                 }
 337                 radix_tree_preload_end();
 338                 ClearPageSwapBacked(new_page);
 339                 __clear_page_locked(new_page);
 340                 /*
 341                  * add_to_swap_cache() doesn't return -EEXIST, so we can safely
 342                  * clear SWAP_HAS_CACHE flag.
 343                  */
 344                 swapcache_free(entry, NULL);
 345         } while (err != -ENOMEM);
 346
 347         if (new_page)
 348                 page_cache_release(new_page);
 349         return found_page;
 350 }
 351
 352 /**
 353  * swapin_readahead - swap in pages in hope we need them soon
 354  * @entry: swap entry of this memory
 355  * @gfp_mask: memory allocation flags
 356  * @vma: user vma this address belongs to
 357  * @addr: target address for mempolicy
 358  *
 359  * Returns the struct page for entry and addr, after queueing swapin.
 360  *
 361  * Primitive swap readahead code. We simply read an aligned block of
 362  * (1 << page_cluster) entries in the swap area. This method is chosen
 363  * because it doesn't cost us any seek time.  We also make sure to queue
 364  * the 'original' request together with the readahead ones...
 365  *
 366  * This has been extended to use the NUMA policies from the mm triggering
 367  * the readahead.
 368  *
 369  * Caller must hold down_read on the vma->vm_mm if vma is not NULL.
 370  */
 371 struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
 372                         struct vm_area_struct *vma, unsigned long addr)
 373 {
 374         int nr_pages;
 375         struct page *page;
 376         unsigned long offset;
 377         unsigned long end_offset;
 378
 379         /*
 380          * Get starting offset for readaround, and number of pages to read.
 381          * Adjust starting address by readbehind (for NUMA interleave case)?
 382          * No, it's very unlikely that swap layout would follow vma layout,
 383          * more likely that neighbouring swap pages came from the same node:
 384          * so use the same "addr" to choose the same node for each swap read.
 385          */
 386         nr_pages = valid_swaphandles(entry, &offset);
 387         for (end_offset = offset + nr_pages; offset < end_offset; offset++) {
 388                 /* Ok, do the async read-ahead now */
 389                 page = read_swap_cache_async(swp_entry(swp_type(entry), offset),
 390                                                 gfp_mask, vma, addr);
 391                 if (!page)
 392                         break;
 393                 page_cache_release(page);
 394         }
 395         lru_add_drain();        /* Push any new pages onto the LRU now */
 396         return read_swap_cache_async(entry, gfp_mask, vma, addr);
 397 }