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/mm.h>
  10 #include <linux/gfp.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/backing-dev.h>
  17 #include <linux/blkdev.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.
  27  */
  28 static const struct address_space_operations swap_aops = {
  29         .writepage      = swap_writepage,
  30         .set_page_dirty = swap_set_page_dirty,
  31         .migratepage    = migrate_page,
  32 };
  33
  34 static struct backing_dev_info swap_backing_dev_info = {
  35         .name           = "swap",
  36         .capabilities   = BDI_CAP_NO_ACCT_AND_WRITEBACK | BDI_CAP_SWAP_BACKED,
  37 };
  38
  39 struct address_space swapper_space = {
  40         .page_tree      = RADIX_TREE_INIT(GFP_ATOMIC|__GFP_NOWARN),
  41         .tree_lock      = __SPIN_LOCK_UNLOCKED(swapper_space.tree_lock),
  42         .a_ops          = &swap_aops,
  43         .i_mmap_nonlinear = LIST_HEAD_INIT(swapper_space.i_mmap_nonlinear),
  44         .backing_dev_info = &swap_backing_dev_info,
  45 };
  46
  47 #define INC_CACHE_INFO(x)       do { swap_cache_info.x++; } while (0)
  48
  49 static struct {
  50         unsigned long add_total;
  51         unsigned long del_total;
  52         unsigned long find_success;
  53         unsigned long find_total;
  54 } swap_cache_info;
  55
  56 void show_swap_cache_info(void)
  57 {
  58         printk("%lu pages in swap cache\n", total_swapcache_pages);
  59         printk("Swap cache stats: add %lu, delete %lu, find %lu/%lu\n",
  60                 swap_cache_info.add_total, swap_cache_info.del_total,
  61                 swap_cache_info.find_success, swap_cache_info.find_total);
  62         printk("Free swap  = %ldkB\n", nr_swap_pages << (PAGE_SHIFT - 10));
  63         printk("Total swap = %lukB\n", total_swap_pages << (PAGE_SHIFT - 10));
  64 }
  65
  66 /*
  67  * __add_to_swap_cache resembles add_to_page_cache_locked on swapper_space,
  68  * but sets SwapCache flag and private instead of mapping and index.
  69  */
  70 static int __add_to_swap_cache(struct page *page, swp_entry_t entry)
  71 {
  72         int error;
  73
  74         VM_BUG_ON(!PageLocked(page));
  75         VM_BUG_ON(PageSwapCache(page));
  76         VM_BUG_ON(!PageSwapBacked(page));
  77
  78         page_cache_get(page);
  79         SetPageSwapCache(page);
  80         set_page_private(page, entry.val);
  81
  82         spin_lock_irq(&swapper_space.tree_lock);
  83         error = radix_tree_insert(&swapper_space.page_tree, entry.val, page);
  84         if (likely(!error)) {
  85                 total_swapcache_pages++;
  86                 __inc_zone_page_state(page, NR_FILE_PAGES);
  87                 INC_CACHE_INFO(add_total);
  88         }
  89         spin_unlock_irq(&swapper_space.tree_lock);
  90
  91         if (unlikely(error)) {
  92                 /*
  93                  * Only the context which have set SWAP_HAS_CACHE flag
  94                  * would call add_to_swap_cache().
  95                  * So add_to_swap_cache() doesn't returns -EEXIST.
  96                  */
  97                 VM_BUG_ON(error == -EEXIST);
  98                 set_page_private(page, 0UL);
  99                 ClearPageSwapCache(page);
 100                 page_cache_release(page);
 101         }
 102
 103         return error;
 104 }
 105
 106
 107 int add_to_swap_cache(struct page *page, swp_entry_t entry, gfp_t gfp_mask)
 108 {
 109         int error;
 110
 111         error = radix_tree_preload(gfp_mask);
 112         if (!error) {
 113                 error = __add_to_swap_cache(page, entry);
 114                 radix_tree_preload_end();
 115         }
 116         return error;
 117 }
 118
 119 /*
 120  * This must be called only on pages that have
 121  * been verified to be in the swap cache.
 122  */
 123 void __delete_from_swap_cache(struct page *page)
 124 {
 125         VM_BUG_ON(!PageLocked(page));
 126         VM_BUG_ON(!PageSwapCache(page));
 127         VM_BUG_ON(PageWriteback(page));
 128
 129         radix_tree_delete(&swapper_space.page_tree, page_private(page));
 130         set_page_private(page, 0);
 131         ClearPageSwapCache(page);
 132         total_swapcache_pages--;
 133         __dec_zone_page_state(page, NR_FILE_PAGES);
 134         INC_CACHE_INFO(del_total);
 135 }
 136
 137 /**
 138  * add_to_swap - allocate swap space for a page
 139  * @page: page we want to move to swap
 140  *
 141  * Allocate swap space for the page and add the page to the
 142  * swap cache.  Caller needs to hold the page lock.
 143  */
 144 int add_to_swap(struct page *page)
 145 {
 146         swp_entry_t entry;
 147         int err;
 148
 149         VM_BUG_ON(!PageLocked(page));
 150         VM_BUG_ON(!PageUptodate(page));
 151
 152         entry = get_swap_page();
 153         if (!entry.val)
 154                 return 0;
 155
 156         if (unlikely(PageTransHuge(page)))
 157                 if (unlikely(split_huge_page(page))) {
 158                         swapcache_free(entry, NULL);
 159                         return 0;
 160                 }
 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_HIGH|__GFP_NOMEMALLOC|__GFP_NOWARN);
 175
 176         if (!err) {     /* Success */
 177                 SetPageDirty(page);
 178                 return 1;
 179         } else {        /* -ENOMEM radix-tree allocation failure */
 180                 /*
 181                  * add_to_swap_cache() doesn't return -EEXIST, so we can safely
 182                  * clear SWAP_HAS_CACHE flag.
 183                  */
 184                 swapcache_free(entry, NULL);
 185                 return 0;
 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         spin_lock_irq(&swapper_space.tree_lock);
 202         __delete_from_swap_cache(page);
 203         spin_unlock_irq(&swapper_space.tree_lock);
 204
 205         swapcache_free(entry, page);
 206         page_cache_release(page);
 207 }
 208
 209 /*
 210  * If we are the only user, then try to free up the swap cache.
 211  *
 212  * Its ok to check for PageSwapCache without the page lock
 213  * here because we are going to recheck again inside
 214  * try_to_free_swap() _with_ the lock.
 215  *                                      - Marcelo
 216  */
 217 static inline void free_swap_cache(struct page *page)
 218 {
 219         if (PageSwapCache(page) && !page_mapped(page) && trylock_page(page)) {
 220                 try_to_free_swap(page);
 221                 unlock_page(page);
 222         }
 223 }
 224
 225 /*
 226  * Perform a free_page(), also freeing any swap cache associated with
 227  * this page if it is the last user of the page.
 228  */
 229 void free_page_and_swap_cache(struct page *page)
 230 {
 231         free_swap_cache(page);
 232         page_cache_release(page);
 233 }
 234
 235 /*
 236  * Passed an array of pages, drop them all from swapcache and then release
 237  * them.  They are removed from the LRU and freed if this is their last use.
 238  */
 239 void free_pages_and_swap_cache(struct page **pages, int nr)
 240 {
 241         struct page **pagep = pages;
 242
 243         lru_add_drain();
 244         while (nr) {
 245                 int todo = min(nr, PAGEVEC_SIZE);
 246                 int i;
 247
 248                 for (i = 0; i < todo; i++)
 249                         free_swap_cache(pagep[i]);
 250                 release_pages(pagep, todo, 0);
 251                 pagep += todo;
 252                 nr -= todo;
 253         }
 254 }
 255
 256 /*
 257  * Lookup a swap entry in the swap cache. A found page will be returned
 258  * unlocked and with its refcount incremented - we rely on the kernel
 259  * lock getting page table operations atomic even if we drop the page
 260  * lock before returning.
 261  */
 262 struct page * lookup_swap_cache(swp_entry_t entry)
 263 {
 264         struct page *page;
 265
 266         page = find_get_page(&swapper_space, entry.val);
 267
 268         if (page)
 269                 INC_CACHE_INFO(find_success);
 270
 271         INC_CACHE_INFO(find_total);
 272         return page;
 273 }
 274
 275 /*
 276  * Locate a page of swap in physical memory, reserving swap cache space
 277  * and reading the disk if it is not already cached.
 278  * A failure return means that either the page allocation failed or that
 279  * the swap entry is no longer in use.
 280  */
 281 struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
 282                         struct vm_area_struct *vma, unsigned long addr)
 283 {
 284         struct page *found_page, *new_page = NULL;
 285         int err;
 286
 287         do {
 288                 /*
 289                  * First check the swap cache.  Since this is normally
 290                  * called after lookup_swap_cache() failed, re-calling
 291                  * that would confuse statistics.
 292                  */
 293                 found_page = find_get_page(&swapper_space, entry.val);
 294                 if (found_page)
 295                         break;
 296
 297                 /*
 298                  * Get a new page to read into from swap.
 299                  */
 300                 if (!new_page) {
 301                         new_page = alloc_page_vma(gfp_mask, vma, addr);
 302                         if (!new_page)
 303                                 break;          /* Out of memory */
 304                 }
 305
 306                 /*
 307                  * call radix_tree_preload() while we can wait.
 308                  */
 309                 err = radix_tree_preload(gfp_mask & GFP_KERNEL);
 310                 if (err)
 311                         break;
 312
 313                 /*
 314                  * Swap entry may have been freed since our caller observed it.
 315                  */
 316                 err = swapcache_prepare(entry);
 317                 if (err == -EEXIST) {   /* seems racy */
 318                         radix_tree_preload_end();
 319                         continue;
 320                 }
 321                 if (err) {              /* swp entry is obsolete ? */
 322                         radix_tree_preload_end();
 323                         break;
 324                 }
 325
 326                 /* May fail (-ENOMEM) if radix-tree node allocation failed. */
 327                 __set_page_locked(new_page);
 328                 SetPageSwapBacked(new_page);
 329                 err = __add_to_swap_cache(new_page, entry);
 330                 if (likely(!err)) {
 331                         radix_tree_preload_end();
 332                         /*
 333                          * Initiate read into locked page and return.
 334                          */
 335                         lru_cache_add_anon(new_page);
 336                         swap_readpage(new_page);
 337                         return new_page;
 338                 }
 339                 radix_tree_preload_end();
 340                 ClearPageSwapBacked(new_page);
 341                 __clear_page_locked(new_page);
 342                 /*
 343                  * add_to_swap_cache() doesn't return -EEXIST, so we can safely
 344                  * clear SWAP_HAS_CACHE flag.
 345                  */
 346                 swapcache_free(entry, NULL);
 347         } while (err != -ENOMEM);
 348
 349         if (new_page)
 350                 page_cache_release(new_page);
 351         return found_page;
 352 }
 353
 354 /**
 355  * swapin_readahead - swap in pages in hope we need them soon
 356  * @entry: swap entry of this memory
 357  * @gfp_mask: memory allocation flags
 358  * @vma: user vma this address belongs to
 359  * @addr: target address for mempolicy
 360  *
 361  * Returns the struct page for entry and addr, after queueing swapin.
 362  *
 363  * Primitive swap readahead code. We simply read an aligned block of
 364  * (1 << page_cluster) entries in the swap area. This method is chosen
 365  * because it doesn't cost us any seek time.  We also make sure to queue
 366  * the 'original' request together with the readahead ones...
 367  *
 368  * This has been extended to use the NUMA policies from the mm triggering
 369  * the readahead.
 370  *
 371  * Caller must hold down_read on the vma->vm_mm if vma is not NULL.
 372  */
 373 struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
 374                         struct vm_area_struct *vma, unsigned long addr)
 375 {
 376         struct page *page;
 377         unsigned long offset = swp_offset(entry);
 378         unsigned long start_offset, end_offset;
 379         unsigned long mask = (1UL << page_cluster) - 1;
 380         struct blk_plug plug;
 381
 382         /* Read a page_cluster sized and aligned cluster around offset. */
 383         start_offset = offset & ~mask;
 384         end_offset = offset | mask;
 385         if (!start_offset)      /* First page is swap header. */
 386                 start_offset++;
 387
 388         blk_start_plug(&plug);
 389         for (offset = start_offset; offset <= end_offset ; offset++) {
 390                 /* Ok, do the async read-ahead now */
 391                 page = read_swap_cache_async(swp_entry(swp_type(entry), offset),
 392                                                 gfp_mask, vma, addr);
 393                 if (!page)
 394                         continue;
 395                 page_cache_release(page);
 396         }
 397         blk_finish_plug(&plug);
 398
 399         lru_add_drain();        /* Push any new pages onto the LRU now */
 400         return read_swap_cache_async(entry, gfp_mask, vma, addr);
 401 }