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
  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.
  26  */
  27 static const struct address_space_operations swap_aops = {
  28         .writepage      = swap_writepage,
  29         .set_page_dirty = swap_set_page_dirty,
  30 #ifdef CONFIG_MIGRATION
  31         .migratepage    = migrate_page,
  32 #endif
  33 };
  34
  35 struct address_space swapper_spaces[MAX_SWAPFILES] = {
  36         [0 ... MAX_SWAPFILES - 1] = {
  37                 .page_tree      = RADIX_TREE_INIT(GFP_ATOMIC|__GFP_NOWARN),
  38                 .i_mmap_writable = ATOMIC_INIT(0),
  39                 .a_ops          = &swap_aops,
  40                 /* swap cache doesn't use writeback related tags */
  41                 .flags          = 1 << AS_NO_WRITEBACK_TAGS,
  42         }
  43 };
  44
  45 #define INC_CACHE_INFO(x)       do { swap_cache_info.x++; } while (0)
  46
  47 static struct {
  48         unsigned long add_total;
  49         unsigned long del_total;
  50         unsigned long find_success;
  51         unsigned long find_total;
  52 } swap_cache_info;
  53
  54 unsigned long total_swapcache_pages(void)
  55 {
  56         int i;
  57         unsigned long ret = 0;
  58
  59         for (i = 0; i < MAX_SWAPFILES; i++)
  60                 ret += swapper_spaces[i].nrpages;
  61         return ret;
  62 }
  63
  64 static atomic_t swapin_readahead_hits = ATOMIC_INIT(4);
  65
  66 void show_swap_cache_info(void)
  67 {
  68         printk("%lu pages in swap cache\n", total_swapcache_pages());
  69         printk("Swap cache stats: add %lu, delete %lu, find %lu/%lu\n",
  70                 swap_cache_info.add_total, swap_cache_info.del_total,
  71                 swap_cache_info.find_success, swap_cache_info.find_total);
  72         printk("Free swap  = %ldkB\n",
  73                 get_nr_swap_pages() << (PAGE_SHIFT - 10));
  74         printk("Total swap = %lukB\n", total_swap_pages << (PAGE_SHIFT - 10));
  75 }
  76
  77 /*
  78  * __add_to_swap_cache resembles add_to_page_cache_locked on swapper_space,
  79  * but sets SwapCache flag and private instead of mapping and index.
  80  */
  81 int __add_to_swap_cache(struct page *page, swp_entry_t entry)
  82 {
  83         int error;
  84         struct address_space *address_space;
  85
  86         VM_BUG_ON_PAGE(!PageLocked(page), page);
  87         VM_BUG_ON_PAGE(PageSwapCache(page), page);
  88         VM_BUG_ON_PAGE(!PageSwapBacked(page), page);
  89
  90         get_page(page);
  91         SetPageSwapCache(page);
  92         set_page_private(page, entry.val);
  93
  94         address_space = swap_address_space(entry);
  95         spin_lock_irq(&address_space->tree_lock);
  96         error = radix_tree_insert(&address_space->page_tree,
  97                                   swp_offset(entry), page);
  98         if (likely(!error)) {
  99                 address_space->nrpages++;
 100                 __inc_node_page_state(page, NR_FILE_PAGES);
 101                 INC_CACHE_INFO(add_total);
 102         }
 103         spin_unlock_irq(&address_space->tree_lock);
 104
 105         if (unlikely(error)) {
 106                 /*
 107                  * Only the context which have set SWAP_HAS_CACHE flag
 108                  * would call add_to_swap_cache().
 109                  * So add_to_swap_cache() doesn't returns -EEXIST.
 110                  */
 111                 VM_BUG_ON(error == -EEXIST);
 112                 set_page_private(page, 0UL);
 113                 ClearPageSwapCache(page);
 114                 put_page(page);
 115         }
 116
 117         return error;
 118 }
 119
 120
 121 int add_to_swap_cache(struct page *page, swp_entry_t entry, gfp_t gfp_mask)
 122 {
 123         int error;
 124
 125         error = radix_tree_maybe_preload(gfp_mask);
 126         if (!error) {
 127                 error = __add_to_swap_cache(page, entry);
 128                 radix_tree_preload_end();
 129         }
 130         return error;
 131 }
 132
 133 /*
 134  * This must be called only on pages that have
 135  * been verified to be in the swap cache.
 136  */
 137 void __delete_from_swap_cache(struct page *page)
 138 {
 139         swp_entry_t entry;
 140         struct address_space *address_space;
 141
 142         VM_BUG_ON_PAGE(!PageLocked(page), page);
 143         VM_BUG_ON_PAGE(!PageSwapCache(page), page);
 144         VM_BUG_ON_PAGE(PageWriteback(page), page);
 145
 146         entry.val = page_private(page);
 147         address_space = swap_address_space(entry);
 148         radix_tree_delete(&address_space->page_tree, swp_offset(entry));
 149         set_page_private(page, 0);
 150         ClearPageSwapCache(page);
 151         address_space->nrpages--;
 152         __dec_node_page_state(page, NR_FILE_PAGES);
 153         INC_CACHE_INFO(del_total);
 154 }
 155
 156 /**
 157  * add_to_swap - allocate swap space for a page
 158  * @page: page we want to move to swap
 159  *
 160  * Allocate swap space for the page and add the page to the
 161  * swap cache.  Caller needs to hold the page lock.
 162  */
 163 int add_to_swap(struct page *page, struct list_head *list)
 164 {
 165         swp_entry_t entry;
 166         int err;
 167
 168         VM_BUG_ON_PAGE(!PageLocked(page), page);
 169         VM_BUG_ON_PAGE(!PageUptodate(page), page);
 170
 171         entry = get_swap_page();
 172         if (!entry.val)
 173                 return 0;
 174
 175         if (mem_cgroup_try_charge_swap(page, entry)) {
 176                 swapcache_free(entry);
 177                 return 0;
 178         }
 179
 180         if (unlikely(PageTransHuge(page)))
 181                 if (unlikely(split_huge_page_to_list(page, list))) {
 182                         swapcache_free(entry);
 183                         return 0;
 184                 }
 185
 186         /*
 187          * Radix-tree node allocations from PF_MEMALLOC contexts could
 188          * completely exhaust the page allocator. __GFP_NOMEMALLOC
 189          * stops emergency reserves from being allocated.
 190          *
 191          * TODO: this could cause a theoretical memory reclaim
 192          * deadlock in the swap out path.
 193          */
 194         /*
 195          * Add it to the swap cache.
 196          */
 197         err = add_to_swap_cache(page, entry,
 198                         __GFP_HIGH|__GFP_NOMEMALLOC|__GFP_NOWARN);
 199
 200         if (!err) {
 201                 return 1;
 202         } else {        /* -ENOMEM radix-tree allocation failure */
 203                 /*
 204                  * add_to_swap_cache() doesn't return -EEXIST, so we can safely
 205                  * clear SWAP_HAS_CACHE flag.
 206                  */
 207                 swapcache_free(entry);
 208                 return 0;
 209         }
 210 }
 211
 212 /*
 213  * This must be called only on pages that have
 214  * been verified to be in the swap cache and locked.
 215  * It will never put the page into the free list,
 216  * the caller has a reference on the page.
 217  */
 218 void delete_from_swap_cache(struct page *page)
 219 {
 220         swp_entry_t entry;
 221         struct address_space *address_space;
 222
 223         entry.val = page_private(page);
 224
 225         address_space = swap_address_space(entry);
 226         spin_lock_irq(&address_space->tree_lock);
 227         __delete_from_swap_cache(page);
 228         spin_unlock_irq(&address_space->tree_lock);
 229
 230         swapcache_free(entry);
 231         put_page(page);
 232 }
 233
 234 /*
 235  * If we are the only user, then try to free up the swap cache.
 236  *
 237  * Its ok to check for PageSwapCache without the page lock
 238  * here because we are going to recheck again inside
 239  * try_to_free_swap() _with_ the lock.
 240  *                                      - Marcelo
 241  */
 242 static inline void free_swap_cache(struct page *page)
 243 {
 244         if (PageSwapCache(page) && !page_mapped(page) && trylock_page(page)) {
 245                 try_to_free_swap(page);
 246                 unlock_page(page);
 247         }
 248 }
 249
 250 /*
 251  * Perform a free_page(), also freeing any swap cache associated with
 252  * this page if it is the last user of the page.
 253  */
 254 void free_page_and_swap_cache(struct page *page)
 255 {
 256         free_swap_cache(page);
 257         if (!is_huge_zero_page(page))
 258                 put_page(page);
 259 }
 260
 261 /*
 262  * Passed an array of pages, drop them all from swapcache and then release
 263  * them.  They are removed from the LRU and freed if this is their last use.
 264  */
 265 void free_pages_and_swap_cache(struct page **pages, int nr)
 266 {
 267         struct page **pagep = pages;
 268         int i;
 269
 270         lru_add_drain();
 271         for (i = 0; i < nr; i++)
 272                 free_swap_cache(pagep[i]);
 273         release_pages(pagep, nr, false);
 274 }
 275
 276 /*
 277  * Lookup a swap entry in the swap cache. A found page will be returned
 278  * unlocked and with its refcount incremented - we rely on the kernel
 279  * lock getting page table operations atomic even if we drop the page
 280  * lock before returning.
 281  */
 282 struct page * lookup_swap_cache(swp_entry_t entry)
 283 {
 284         struct page *page;
 285
 286         page = find_get_page(swap_address_space(entry), swp_offset(entry));
 287
 288         if (page) {
 289                 INC_CACHE_INFO(find_success);
 290                 if (TestClearPageReadahead(page))
 291                         atomic_inc(&swapin_readahead_hits);
 292         }
 293
 294         INC_CACHE_INFO(find_total);
 295         return page;
 296 }
 297
 298 struct page *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
 299                         struct vm_area_struct *vma, unsigned long addr,
 300                         bool *new_page_allocated)
 301 {
 302         struct page *found_page, *new_page = NULL;
 303         struct address_space *swapper_space = swap_address_space(entry);
 304         int err;
 305         *new_page_allocated = false;
 306
 307         do {
 308                 /*
 309                  * First check the swap cache.  Since this is normally
 310                  * called after lookup_swap_cache() failed, re-calling
 311                  * that would confuse statistics.
 312                  */
 313                 found_page = find_get_page(swapper_space, swp_offset(entry));
 314                 if (found_page)
 315                         break;
 316
 317                 /*
 318                  * Get a new page to read into from swap.
 319                  */
 320                 if (!new_page) {
 321                         new_page = alloc_page_vma(gfp_mask, vma, addr);
 322                         if (!new_page)
 323                                 break;          /* Out of memory */
 324                 }
 325
 326                 /*
 327                  * call radix_tree_preload() while we can wait.
 328                  */
 329                 err = radix_tree_maybe_preload(gfp_mask & GFP_KERNEL);
 330                 if (err)
 331                         break;
 332
 333                 /*
 334                  * Swap entry may have been freed since our caller observed it.
 335                  */
 336                 err = swapcache_prepare(entry);
 337                 if (err == -EEXIST) {
 338                         radix_tree_preload_end();
 339                         /*
 340                          * We might race against get_swap_page() and stumble
 341                          * across a SWAP_HAS_CACHE swap_map entry whose page
 342                          * has not been brought into the swapcache yet, while
 343                          * the other end is scheduled away waiting on discard
 344                          * I/O completion at scan_swap_map().
 345                          *
 346                          * In order to avoid turning this transitory state
 347                          * into a permanent loop around this -EEXIST case
 348                          * if !CONFIG_PREEMPT and the I/O completion happens
 349                          * to be waiting on the CPU waitqueue where we are now
 350                          * busy looping, we just conditionally invoke the
 351                          * scheduler here, if there are some more important
 352                          * tasks to run.
 353                          */
 354                         cond_resched();
 355                         continue;
 356                 }
 357                 if (err) {              /* swp entry is obsolete ? */
 358                         radix_tree_preload_end();
 359                         break;
 360                 }
 361
 362                 /* May fail (-ENOMEM) if radix-tree node allocation failed. */
 363                 __SetPageLocked(new_page);
 364                 __SetPageSwapBacked(new_page);
 365                 err = __add_to_swap_cache(new_page, entry);
 366                 if (likely(!err)) {
 367                         radix_tree_preload_end();
 368                         /*
 369                          * Initiate read into locked page and return.
 370                          */
 371                         lru_cache_add_anon(new_page);
 372                         *new_page_allocated = true;
 373                         return new_page;
 374                 }
 375                 radix_tree_preload_end();
 376                 __ClearPageLocked(new_page);
 377                 /*
 378                  * add_to_swap_cache() doesn't return -EEXIST, so we can safely
 379                  * clear SWAP_HAS_CACHE flag.
 380                  */
 381                 swapcache_free(entry);
 382         } while (err != -ENOMEM);
 383
 384         if (new_page)
 385                 put_page(new_page);
 386         return found_page;
 387 }
 388
 389 /*
 390  * Locate a page of swap in physical memory, reserving swap cache space
 391  * and reading the disk if it is not already cached.
 392  * A failure return means that either the page allocation failed or that
 393  * the swap entry is no longer in use.
 394  */
 395 struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
 396                         struct vm_area_struct *vma, unsigned long addr)
 397 {
 398         bool page_was_allocated;
 399         struct page *retpage = __read_swap_cache_async(entry, gfp_mask,
 400                         vma, addr, &page_was_allocated);
 401
 402         if (page_was_allocated)
 403                 swap_readpage(retpage);
 404
 405         return retpage;
 406 }
 407
 408 static unsigned long swapin_nr_pages(unsigned long offset)
 409 {
 410         static unsigned long prev_offset;
 411         unsigned int pages, max_pages, last_ra;
 412         static atomic_t last_readahead_pages;
 413
 414         max_pages = 1 << READ_ONCE(page_cluster);
 415         if (max_pages <= 1)
 416                 return 1;
 417
 418         /*
 419          * This heuristic has been found to work well on both sequential and
 420          * random loads, swapping to hard disk or to SSD: please don't ask
 421          * what the "+ 2" means, it just happens to work well, that's all.
 422          */
 423         pages = atomic_xchg(&swapin_readahead_hits, 0) + 2;
 424         if (pages == 2) {
 425                 /*
 426                  * We can have no readahead hits to judge by: but must not get
 427                  * stuck here forever, so check for an adjacent offset instead
 428                  * (and don't even bother to check whether swap type is same).
 429                  */
 430                 if (offset != prev_offset + 1 && offset != prev_offset - 1)
 431                         pages = 1;
 432                 prev_offset = offset;
 433         } else {
 434                 unsigned int roundup = 4;
 435                 while (roundup < pages)
 436                         roundup <<= 1;
 437                 pages = roundup;
 438         }
 439
 440         if (pages > max_pages)
 441                 pages = max_pages;
 442
 443         /* Don't shrink readahead too fast */
 444         last_ra = atomic_read(&last_readahead_pages) / 2;
 445         if (pages < last_ra)
 446                 pages = last_ra;
 447         atomic_set(&last_readahead_pages, pages);
 448
 449         return pages;
 450 }
 451
 452 /**
 453  * swapin_readahead - swap in pages in hope we need them soon
 454  * @entry: swap entry of this memory
 455  * @gfp_mask: memory allocation flags
 456  * @vma: user vma this address belongs to
 457  * @addr: target address for mempolicy
 458  *
 459  * Returns the struct page for entry and addr, after queueing swapin.
 460  *
 461  * Primitive swap readahead code. We simply read an aligned block of
 462  * (1 << page_cluster) entries in the swap area. This method is chosen
 463  * because it doesn't cost us any seek time.  We also make sure to queue
 464  * the 'original' request together with the readahead ones...
 465  *
 466  * This has been extended to use the NUMA policies from the mm triggering
 467  * the readahead.
 468  *
 469  * Caller must hold down_read on the vma->vm_mm if vma is not NULL.
 470  */
 471 struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
 472                         struct vm_area_struct *vma, unsigned long addr)
 473 {
 474         struct page *page;
 475         unsigned long entry_offset = swp_offset(entry);
 476         unsigned long offset = entry_offset;
 477         unsigned long start_offset, end_offset;
 478         unsigned long mask;
 479         struct blk_plug plug;
 480
 481         mask = swapin_nr_pages(offset) - 1;
 482         if (!mask)
 483                 goto skip;
 484
 485         /* Read a page_cluster sized and aligned cluster around offset. */
 486         start_offset = offset & ~mask;
 487         end_offset = offset | mask;
 488         if (!start_offset)      /* First page is swap header. */
 489                 start_offset++;
 490
 491         blk_start_plug(&plug);
 492         for (offset = start_offset; offset <= end_offset ; offset++) {
 493                 /* Ok, do the async read-ahead now */
 494                 page = read_swap_cache_async(swp_entry(swp_type(entry), offset),
 495                                                 gfp_mask, vma, addr);
 496                 if (!page)
 497                         continue;
 498                 if (offset != entry_offset)
 499                         SetPageReadahead(page);
 500                 put_page(page);
 501         }
 502         blk_finish_plug(&plug);
 503
 504         lru_add_drain();        /* Push any new pages onto the LRU now */
 505 skip:
 506         return read_swap_cache_async(entry, gfp_mask, vma, addr);
 507 }