linux/mm/swap_state.c
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   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 */
  28static 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
  34static 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
  39struct 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
  49static 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
  56void 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 */
  70static 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
 107int 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 */
 123void __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 */
 144int 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 */
 195void 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 */
 217static 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 */
 229void 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 */
 239void 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 */
 262struct 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 */
 281struct 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 */
 373struct 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}
 402
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