linux/mm/page_io.c
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   1/*
   2 *  linux/mm/page_io.c
   3 *
   4 *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
   5 *
   6 *  Swap reorganised 29.12.95, 
   7 *  Asynchronous swapping added 30.12.95. Stephen Tweedie
   8 *  Removed race in async swapping. 14.4.1996. Bruno Haible
   9 *  Add swap of shared pages through the page cache. 20.2.1998. Stephen Tweedie
  10 *  Always use brw_page, life becomes simpler. 12 May 1998 Eric Biederman
  11 */
  12
  13#include <linux/mm.h>
  14#include <linux/kernel_stat.h>
  15#include <linux/gfp.h>
  16#include <linux/pagemap.h>
  17#include <linux/swap.h>
  18#include <linux/bio.h>
  19#include <linux/swapops.h>
  20#include <linux/buffer_head.h>
  21#include <linux/writeback.h>
  22#include <linux/frontswap.h>
  23#include <linux/aio.h>
  24#include <linux/blkdev.h>
  25#include <asm/pgtable.h>
  26
  27static struct bio *get_swap_bio(gfp_t gfp_flags,
  28                                struct page *page, bio_end_io_t end_io)
  29{
  30        struct bio *bio;
  31
  32        bio = bio_alloc(gfp_flags, 1);
  33        if (bio) {
  34                bio->bi_sector = map_swap_page(page, &bio->bi_bdev);
  35                bio->bi_sector <<= PAGE_SHIFT - 9;
  36                bio->bi_io_vec[0].bv_page = page;
  37                bio->bi_io_vec[0].bv_len = PAGE_SIZE;
  38                bio->bi_io_vec[0].bv_offset = 0;
  39                bio->bi_vcnt = 1;
  40                bio->bi_size = PAGE_SIZE;
  41                bio->bi_end_io = end_io;
  42        }
  43        return bio;
  44}
  45
  46void end_swap_bio_write(struct bio *bio, int err)
  47{
  48        const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
  49        struct page *page = bio->bi_io_vec[0].bv_page;
  50
  51        if (!uptodate) {
  52                SetPageError(page);
  53                /*
  54                 * We failed to write the page out to swap-space.
  55                 * Re-dirty the page in order to avoid it being reclaimed.
  56                 * Also print a dire warning that things will go BAD (tm)
  57                 * very quickly.
  58                 *
  59                 * Also clear PG_reclaim to avoid rotate_reclaimable_page()
  60                 */
  61                set_page_dirty(page);
  62                printk(KERN_ALERT "Write-error on swap-device (%u:%u:%Lu)\n",
  63                                imajor(bio->bi_bdev->bd_inode),
  64                                iminor(bio->bi_bdev->bd_inode),
  65                                (unsigned long long)bio->bi_sector);
  66                ClearPageReclaim(page);
  67        }
  68        end_page_writeback(page);
  69        bio_put(bio);
  70}
  71
  72void end_swap_bio_read(struct bio *bio, int err)
  73{
  74        const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
  75        struct page *page = bio->bi_io_vec[0].bv_page;
  76
  77        if (!uptodate) {
  78                SetPageError(page);
  79                ClearPageUptodate(page);
  80                printk(KERN_ALERT "Read-error on swap-device (%u:%u:%Lu)\n",
  81                                imajor(bio->bi_bdev->bd_inode),
  82                                iminor(bio->bi_bdev->bd_inode),
  83                                (unsigned long long)bio->bi_sector);
  84                goto out;
  85        }
  86
  87        SetPageUptodate(page);
  88
  89        /*
  90         * There is no guarantee that the page is in swap cache - the software
  91         * suspend code (at least) uses end_swap_bio_read() against a non-
  92         * swapcache page.  So we must check PG_swapcache before proceeding with
  93         * this optimization.
  94         */
  95        if (likely(PageSwapCache(page))) {
  96                struct swap_info_struct *sis;
  97
  98                sis = page_swap_info(page);
  99                if (sis->flags & SWP_BLKDEV) {
 100                        /*
 101                         * The swap subsystem performs lazy swap slot freeing,
 102                         * expecting that the page will be swapped out again.
 103                         * So we can avoid an unnecessary write if the page
 104                         * isn't redirtied.
 105                         * This is good for real swap storage because we can
 106                         * reduce unnecessary I/O and enhance wear-leveling
 107                         * if an SSD is used as the as swap device.
 108                         * But if in-memory swap device (eg zram) is used,
 109                         * this causes a duplicated copy between uncompressed
 110                         * data in VM-owned memory and compressed data in
 111                         * zram-owned memory.  So let's free zram-owned memory
 112                         * and make the VM-owned decompressed page *dirty*,
 113                         * so the page should be swapped out somewhere again if
 114                         * we again wish to reclaim it.
 115                         */
 116                        struct gendisk *disk = sis->bdev->bd_disk;
 117                        if (disk->fops->swap_slot_free_notify) {
 118                                swp_entry_t entry;
 119                                unsigned long offset;
 120
 121                                entry.val = page_private(page);
 122                                offset = swp_offset(entry);
 123
 124                                SetPageDirty(page);
 125                                disk->fops->swap_slot_free_notify(sis->bdev,
 126                                                offset);
 127                        }
 128                }
 129        }
 130
 131out:
 132        unlock_page(page);
 133        bio_put(bio);
 134}
 135
 136int generic_swapfile_activate(struct swap_info_struct *sis,
 137                                struct file *swap_file,
 138                                sector_t *span)
 139{
 140        struct address_space *mapping = swap_file->f_mapping;
 141        struct inode *inode = mapping->host;
 142        unsigned blocks_per_page;
 143        unsigned long page_no;
 144        unsigned blkbits;
 145        sector_t probe_block;
 146        sector_t last_block;
 147        sector_t lowest_block = -1;
 148        sector_t highest_block = 0;
 149        int nr_extents = 0;
 150        int ret;
 151
 152        blkbits = inode->i_blkbits;
 153        blocks_per_page = PAGE_SIZE >> blkbits;
 154
 155        /*
 156         * Map all the blocks into the extent list.  This code doesn't try
 157         * to be very smart.
 158         */
 159        probe_block = 0;
 160        page_no = 0;
 161        last_block = i_size_read(inode) >> blkbits;
 162        while ((probe_block + blocks_per_page) <= last_block &&
 163                        page_no < sis->max) {
 164                unsigned block_in_page;
 165                sector_t first_block;
 166
 167                first_block = bmap(inode, probe_block);
 168                if (first_block == 0)
 169                        goto bad_bmap;
 170
 171                /*
 172                 * It must be PAGE_SIZE aligned on-disk
 173                 */
 174                if (first_block & (blocks_per_page - 1)) {
 175                        probe_block++;
 176                        goto reprobe;
 177                }
 178
 179                for (block_in_page = 1; block_in_page < blocks_per_page;
 180                                        block_in_page++) {
 181                        sector_t block;
 182
 183                        block = bmap(inode, probe_block + block_in_page);
 184                        if (block == 0)
 185                                goto bad_bmap;
 186                        if (block != first_block + block_in_page) {
 187                                /* Discontiguity */
 188                                probe_block++;
 189                                goto reprobe;
 190                        }
 191                }
 192
 193                first_block >>= (PAGE_SHIFT - blkbits);
 194                if (page_no) {  /* exclude the header page */
 195                        if (first_block < lowest_block)
 196                                lowest_block = first_block;
 197                        if (first_block > highest_block)
 198                                highest_block = first_block;
 199                }
 200
 201                /*
 202                 * We found a PAGE_SIZE-length, PAGE_SIZE-aligned run of blocks
 203                 */
 204                ret = add_swap_extent(sis, page_no, 1, first_block);
 205                if (ret < 0)
 206                        goto out;
 207                nr_extents += ret;
 208                page_no++;
 209                probe_block += blocks_per_page;
 210reprobe:
 211                continue;
 212        }
 213        ret = nr_extents;
 214        *span = 1 + highest_block - lowest_block;
 215        if (page_no == 0)
 216                page_no = 1;    /* force Empty message */
 217        sis->max = page_no;
 218        sis->pages = page_no - 1;
 219        sis->highest_bit = page_no - 1;
 220out:
 221        return ret;
 222bad_bmap:
 223        printk(KERN_ERR "swapon: swapfile has holes\n");
 224        ret = -EINVAL;
 225        goto out;
 226}
 227
 228/*
 229 * We may have stale swap cache pages in memory: notice
 230 * them here and get rid of the unnecessary final write.
 231 */
 232int swap_writepage(struct page *page, struct writeback_control *wbc)
 233{
 234        int ret = 0;
 235
 236        if (try_to_free_swap(page)) {
 237                unlock_page(page);
 238                goto out;
 239        }
 240        if (frontswap_store(page) == 0) {
 241                set_page_writeback(page);
 242                unlock_page(page);
 243                end_page_writeback(page);
 244                goto out;
 245        }
 246        ret = __swap_writepage(page, wbc, end_swap_bio_write);
 247out:
 248        return ret;
 249}
 250
 251int __swap_writepage(struct page *page, struct writeback_control *wbc,
 252        void (*end_write_func)(struct bio *, int))
 253{
 254        struct bio *bio;
 255        int ret = 0, rw = WRITE;
 256        struct swap_info_struct *sis = page_swap_info(page);
 257
 258        if (sis->flags & SWP_FILE) {
 259                struct kiocb kiocb;
 260                struct file *swap_file = sis->swap_file;
 261                struct address_space *mapping = swap_file->f_mapping;
 262                struct iovec iov = {
 263                        .iov_base = kmap(page),
 264                        .iov_len  = PAGE_SIZE,
 265                };
 266
 267                init_sync_kiocb(&kiocb, swap_file);
 268                kiocb.ki_pos = page_file_offset(page);
 269                kiocb.ki_left = PAGE_SIZE;
 270                kiocb.ki_nbytes = PAGE_SIZE;
 271
 272                set_page_writeback(page);
 273                unlock_page(page);
 274                ret = mapping->a_ops->direct_IO(KERNEL_WRITE,
 275                                                &kiocb, &iov,
 276                                                kiocb.ki_pos, 1);
 277                kunmap(page);
 278                if (ret == PAGE_SIZE) {
 279                        count_vm_event(PSWPOUT);
 280                        ret = 0;
 281                } else {
 282                        /*
 283                         * In the case of swap-over-nfs, this can be a
 284                         * temporary failure if the system has limited
 285                         * memory for allocating transmit buffers.
 286                         * Mark the page dirty and avoid
 287                         * rotate_reclaimable_page but rate-limit the
 288                         * messages but do not flag PageError like
 289                         * the normal direct-to-bio case as it could
 290                         * be temporary.
 291                         */
 292                        set_page_dirty(page);
 293                        ClearPageReclaim(page);
 294                        pr_err_ratelimited("Write error on dio swapfile (%Lu)\n",
 295                                page_file_offset(page));
 296                }
 297                end_page_writeback(page);
 298                return ret;
 299        }
 300
 301        bio = get_swap_bio(GFP_NOIO, page, end_write_func);
 302        if (bio == NULL) {
 303                set_page_dirty(page);
 304                unlock_page(page);
 305                ret = -ENOMEM;
 306                goto out;
 307        }
 308        if (wbc->sync_mode == WB_SYNC_ALL)
 309                rw |= REQ_SYNC;
 310        count_vm_event(PSWPOUT);
 311        set_page_writeback(page);
 312        unlock_page(page);
 313        submit_bio(rw, bio);
 314out:
 315        return ret;
 316}
 317
 318int swap_readpage(struct page *page)
 319{
 320        struct bio *bio;
 321        int ret = 0;
 322        struct swap_info_struct *sis = page_swap_info(page);
 323
 324        VM_BUG_ON(!PageLocked(page));
 325        VM_BUG_ON(PageUptodate(page));
 326        if (frontswap_load(page) == 0) {
 327                SetPageUptodate(page);
 328                unlock_page(page);
 329                goto out;
 330        }
 331
 332        if (sis->flags & SWP_FILE) {
 333                struct file *swap_file = sis->swap_file;
 334                struct address_space *mapping = swap_file->f_mapping;
 335
 336                ret = mapping->a_ops->readpage(swap_file, page);
 337                if (!ret)
 338                        count_vm_event(PSWPIN);
 339                return ret;
 340        }
 341
 342        bio = get_swap_bio(GFP_KERNEL, page, end_swap_bio_read);
 343        if (bio == NULL) {
 344                unlock_page(page);
 345                ret = -ENOMEM;
 346                goto out;
 347        }
 348        count_vm_event(PSWPIN);
 349        submit_bio(READ, bio);
 350out:
 351        return ret;
 352}
 353
 354int swap_set_page_dirty(struct page *page)
 355{
 356        struct swap_info_struct *sis = page_swap_info(page);
 357
 358        if (sis->flags & SWP_FILE) {
 359                struct address_space *mapping = sis->swap_file->f_mapping;
 360                return mapping->a_ops->set_page_dirty(page);
 361        } else {
 362                return __set_page_dirty_no_writeback(page);
 363        }
 364}
 365
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