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/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.
  28 */
  29static const struct address_space_operations swap_aops = {
  30        .writepage      = swap_writepage,
  31        .set_page_dirty = __set_page_dirty_nobuffers,
  32        .migratepage    = migrate_page,
  33};
  34
  35static struct backing_dev_info swap_backing_dev_info = {
  36        .name           = "swap",
  37        .capabilities   = BDI_CAP_NO_ACCT_AND_WRITEBACK | BDI_CAP_SWAP_BACKED,
  38};
  39
  40struct address_space swapper_space = {
  41        .page_tree      = RADIX_TREE_INIT(GFP_ATOMIC|__GFP_NOWARN),
  42        .tree_lock      = __SPIN_LOCK_UNLOCKED(swapper_space.tree_lock),
  43        .a_ops          = &swap_aops,
  44        .i_mmap_nonlinear = LIST_HEAD_INIT(swapper_space.i_mmap_nonlinear),
  45        .backing_dev_info = &swap_backing_dev_info,
  46};
  47
  48#define INC_CACHE_INFO(x)       do { swap_cache_info.x++; } while (0)
  49
  50static struct {
  51        unsigned long add_total;
  52        unsigned long del_total;
  53        unsigned long find_success;
  54        unsigned long find_total;
  55} swap_cache_info;
  56
  57void show_swap_cache_info(void)
  58{
  59        printk("%lu pages in swap cache\n", total_swapcache_pages);
  60        printk("Swap cache stats: add %lu, delete %lu, find %lu/%lu\n",
  61                swap_cache_info.add_total, swap_cache_info.del_total,
  62                swap_cache_info.find_success, swap_cache_info.find_total);
  63        printk("Free swap  = %ldkB\n", nr_swap_pages << (PAGE_SHIFT - 10));
  64        printk("Total swap = %lukB\n", total_swap_pages << (PAGE_SHIFT - 10));
  65}
  66
  67/*
  68 * __add_to_swap_cache resembles add_to_page_cache_locked on swapper_space,
  69 * but sets SwapCache flag and private instead of mapping and index.
  70 */
  71static int __add_to_swap_cache(struct page *page, swp_entry_t entry)
  72{
  73        int error;
  74
  75        VM_BUG_ON(!PageLocked(page));
  76        VM_BUG_ON(PageSwapCache(page));
  77        VM_BUG_ON(!PageSwapBacked(page));
  78
  79        page_cache_get(page);
  80        SetPageSwapCache(page);
  81        set_page_private(page, entry.val);
  82
  83        spin_lock_irq(&swapper_space.tree_lock);
  84        error = radix_tree_insert(&swapper_space.page_tree, entry.val, page);
  85        if (likely(!error)) {
  86                total_swapcache_pages++;
  87                __inc_zone_page_state(page, NR_FILE_PAGES);
  88                INC_CACHE_INFO(add_total);
  89        }
  90        spin_unlock_irq(&swapper_space.tree_lock);
  91
  92        if (unlikely(error)) {
  93                /*
  94                 * Only the context which have set SWAP_HAS_CACHE flag
  95                 * would call add_to_swap_cache().
  96                 * So add_to_swap_cache() doesn't returns -EEXIST.
  97                 */
  98                VM_BUG_ON(error == -EEXIST);
  99                set_page_private(page, 0UL);
 100                ClearPageSwapCache(page);
 101                page_cache_release(page);
 102        }
 103
 104        return error;
 105}
 106
 107
 108int add_to_swap_cache(struct page *page, swp_entry_t entry, gfp_t gfp_mask)
 109{
 110        int error;
 111
 112        error = radix_tree_preload(gfp_mask);
 113        if (!error) {
 114                error = __add_to_swap_cache(page, entry);
 115                radix_tree_preload_end();
 116        }
 117        return error;
 118}
 119
 120/*
 121 * This must be called only on pages that have
 122 * been verified to be in the swap cache.
 123 */
 124void __delete_from_swap_cache(struct page *page)
 125{
 126        VM_BUG_ON(!PageLocked(page));
 127        VM_BUG_ON(!PageSwapCache(page));
 128        VM_BUG_ON(PageWriteback(page));
 129
 130        radix_tree_delete(&swapper_space.page_tree, page_private(page));
 131        set_page_private(page, 0);
 132        ClearPageSwapCache(page);
 133        total_swapcache_pages--;
 134        __dec_zone_page_state(page, NR_FILE_PAGES);
 135        INC_CACHE_INFO(del_total);
 136}
 137
 138/**
 139 * add_to_swap - allocate swap space for a page
 140 * @page: page we want to move to swap
 141 *
 142 * Allocate swap space for the page and add the page to the
 143 * swap cache.  Caller needs to hold the page lock. 
 144 */
 145int add_to_swap(struct page *page)
 146{
 147        swp_entry_t entry;
 148        int err;
 149
 150        VM_BUG_ON(!PageLocked(page));
 151        VM_BUG_ON(!PageUptodate(page));
 152
 153        entry = get_swap_page();
 154        if (!entry.val)
 155                return 0;
 156
 157        if (unlikely(PageTransHuge(page)))
 158                if (unlikely(split_huge_page(page))) {
 159                        swapcache_free(entry, NULL);
 160                        return 0;
 161                }
 162
 163        /*
 164         * Radix-tree node allocations from PF_MEMALLOC contexts could
 165         * completely exhaust the page allocator. __GFP_NOMEMALLOC
 166         * stops emergency reserves from being allocated.
 167         *
 168         * TODO: this could cause a theoretical memory reclaim
 169         * deadlock in the swap out path.
 170         */
 171        /*
 172         * Add it to the swap cache and mark it dirty
 173         */
 174        err = add_to_swap_cache(page, entry,
 175                        __GFP_HIGH|__GFP_NOMEMALLOC|__GFP_NOWARN);
 176
 177        if (!err) {     /* Success */
 178                SetPageDirty(page);
 179                return 1;
 180        } else {        /* -ENOMEM radix-tree allocation failure */
 181                /*
 182                 * add_to_swap_cache() doesn't return -EEXIST, so we can safely
 183                 * clear SWAP_HAS_CACHE flag.
 184                 */
 185                swapcache_free(entry, NULL);
 186                return 0;
 187        }
 188}
 189
 190/*
 191 * This must be called only on pages that have
 192 * been verified to be in the swap cache and locked.
 193 * It will never put the page into the free list,
 194 * the caller has a reference on the page.
 195 */
 196void delete_from_swap_cache(struct page *page)
 197{
 198        swp_entry_t entry;
 199
 200        entry.val = page_private(page);
 201
 202        spin_lock_irq(&swapper_space.tree_lock);
 203        __delete_from_swap_cache(page);
 204        spin_unlock_irq(&swapper_space.tree_lock);
 205
 206        swapcache_free(entry, page);
 207        page_cache_release(page);
 208}
 209
 210/* 
 211 * If we are the only user, then try to free up the swap cache. 
 212 * 
 213 * Its ok to check for PageSwapCache without the page lock
 214 * here because we are going to recheck again inside
 215 * try_to_free_swap() _with_ the lock.
 216 *                                      - Marcelo
 217 */
 218static inline void free_swap_cache(struct page *page)
 219{
 220        if (PageSwapCache(page) && !page_mapped(page) && trylock_page(page)) {
 221                try_to_free_swap(page);
 222                unlock_page(page);
 223        }
 224}
 225
 226/* 
 227 * Perform a free_page(), also freeing any swap cache associated with
 228 * this page if it is the last user of the page.
 229 */
 230void free_page_and_swap_cache(struct page *page)
 231{
 232        free_swap_cache(page);
 233        page_cache_release(page);
 234}
 235
 236/*
 237 * Passed an array of pages, drop them all from swapcache and then release
 238 * them.  They are removed from the LRU and freed if this is their last use.
 239 */
 240void free_pages_and_swap_cache(struct page **pages, int nr)
 241{
 242        struct page **pagep = pages;
 243
 244        lru_add_drain();
 245        while (nr) {
 246                int todo = min(nr, PAGEVEC_SIZE);
 247                int i;
 248
 249                for (i = 0; i < todo; i++)
 250                        free_swap_cache(pagep[i]);
 251                release_pages(pagep, todo, 0);
 252                pagep += todo;
 253                nr -= todo;
 254        }
 255}
 256
 257/*
 258 * Lookup a swap entry in the swap cache. A found page will be returned
 259 * unlocked and with its refcount incremented - we rely on the kernel
 260 * lock getting page table operations atomic even if we drop the page
 261 * lock before returning.
 262 */
 263struct page * lookup_swap_cache(swp_entry_t entry)
 264{
 265        struct page *page;
 266
 267        page = find_get_page(&swapper_space, entry.val);
 268
 269        if (page)
 270                INC_CACHE_INFO(find_success);
 271
 272        INC_CACHE_INFO(find_total);
 273        return page;
 274}
 275
 276/* 
 277 * Locate a page of swap in physical memory, reserving swap cache space
 278 * and reading the disk if it is not already cached.
 279 * A failure return means that either the page allocation failed or that
 280 * the swap entry is no longer in use.
 281 */
 282struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
 283                        struct vm_area_struct *vma, unsigned long addr)
 284{
 285        struct page *found_page, *new_page = NULL;
 286        int err;
 287
 288        do {
 289                /*
 290                 * First check the swap cache.  Since this is normally
 291                 * called after lookup_swap_cache() failed, re-calling
 292                 * that would confuse statistics.
 293                 */
 294                found_page = find_get_page(&swapper_space, entry.val);
 295                if (found_page)
 296                        break;
 297
 298                /*
 299                 * Get a new page to read into from swap.
 300                 */
 301                if (!new_page) {
 302                        new_page = alloc_page_vma(gfp_mask, vma, addr);
 303                        if (!new_page)
 304                                break;          /* Out of memory */
 305                }
 306
 307                /*
 308                 * call radix_tree_preload() while we can wait.
 309                 */
 310                err = radix_tree_preload(gfp_mask & GFP_KERNEL);
 311                if (err)
 312                        break;
 313
 314                /*
 315                 * Swap entry may have been freed since our caller observed it.
 316                 */
 317                err = swapcache_prepare(entry);
 318                if (err == -EEXIST) {   /* seems racy */
 319                        radix_tree_preload_end();
 320                        continue;
 321                }
 322                if (err) {              /* swp entry is obsolete ? */
 323                        radix_tree_preload_end();
 324                        break;
 325                }
 326
 327                /* May fail (-ENOMEM) if radix-tree node allocation failed. */
 328                __set_page_locked(new_page);
 329                SetPageSwapBacked(new_page);
 330                err = __add_to_swap_cache(new_page, entry);
 331                if (likely(!err)) {
 332                        radix_tree_preload_end();
 333                        /*
 334                         * Initiate read into locked page and return.
 335                         */
 336                        lru_cache_add_anon(new_page);
 337                        swap_readpage(new_page);
 338                        return new_page;
 339                }
 340                radix_tree_preload_end();
 341                ClearPageSwapBacked(new_page);
 342                __clear_page_locked(new_page);
 343                /*
 344                 * add_to_swap_cache() doesn't return -EEXIST, so we can safely
 345                 * clear SWAP_HAS_CACHE flag.
 346                 */
 347                swapcache_free(entry, NULL);
 348        } while (err != -ENOMEM);
 349
 350        if (new_page)
 351                page_cache_release(new_page);
 352        return found_page;
 353}
 354
 355/**
 356 * swapin_readahead - swap in pages in hope we need them soon
 357 * @entry: swap entry of this memory
 358 * @gfp_mask: memory allocation flags
 359 * @vma: user vma this address belongs to
 360 * @addr: target address for mempolicy
 361 *
 362 * Returns the struct page for entry and addr, after queueing swapin.
 363 *
 364 * Primitive swap readahead code. We simply read an aligned block of
 365 * (1 << page_cluster) entries in the swap area. This method is chosen
 366 * because it doesn't cost us any seek time.  We also make sure to queue
 367 * the 'original' request together with the readahead ones...
 368 *
 369 * This has been extended to use the NUMA policies from the mm triggering
 370 * the readahead.
 371 *
 372 * Caller must hold down_read on the vma->vm_mm if vma is not NULL.
 373 */
 374struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
 375                        struct vm_area_struct *vma, unsigned long addr)
 376{
 377        int nr_pages;
 378        struct page *page;
 379        unsigned long offset;
 380        unsigned long end_offset;
 381
 382        /*
 383         * Get starting offset for readaround, and number of pages to read.
 384         * Adjust starting address by readbehind (for NUMA interleave case)?
 385         * No, it's very unlikely that swap layout would follow vma layout,
 386         * more likely that neighbouring swap pages came from the same node:
 387         * so use the same "addr" to choose the same node for each swap read.
 388         */
 389        nr_pages = valid_swaphandles(entry, &offset);
 390        for (end_offset = offset + nr_pages; offset < end_offset; offset++) {
 391                /* Ok, do the async read-ahead now */
 392                page = read_swap_cache_async(swp_entry(swp_type(entry), offset),
 393                                                gfp_mask, vma, addr);
 394                if (!page)
 395                        break;
 396                page_cache_release(page);
 397        }
 398        lru_add_drain();        /* Push any new pages onto the LRU now */
 399        return read_swap_cache_async(entry, gfp_mask, vma, addr);
 400}
 401
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