mm/page_io.c

   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/blkdev.h>
  24 #include <linux/uio.h>
  25 #include <asm/pgtable.h>
  26
  27 static 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_iter.bi_sector = map_swap_page(page, &bio->bi_bdev);
  35                 bio->bi_iter.bi_sector <<= PAGE_SHIFT - 9;
  36                 bio->bi_end_io = end_io;
  37
  38                 bio_add_page(bio, page, PAGE_SIZE, 0);
  39                 BUG_ON(bio->bi_iter.bi_size != PAGE_SIZE);
  40         }
  41         return bio;
  42 }
  43
  44 void end_swap_bio_write(struct bio *bio)
  45 {
  46         struct page *page = bio->bi_io_vec[0].bv_page;
  47
  48         if (bio->bi_error) {
  49                 SetPageError(page);
  50                 /*
  51                  * We failed to write the page out to swap-space.
  52                  * Re-dirty the page in order to avoid it being reclaimed.
  53                  * Also print a dire warning that things will go BAD (tm)
  54                  * very quickly.
  55                  *
  56                  * Also clear PG_reclaim to avoid rotate_reclaimable_page()
  57                  */
  58                 set_page_dirty(page);
  59                 pr_alert("Write-error on swap-device (%u:%u:%llu)\n",
  60                          imajor(bio->bi_bdev->bd_inode),
  61                          iminor(bio->bi_bdev->bd_inode),
  62                          (unsigned long long)bio->bi_iter.bi_sector);
  63                 ClearPageReclaim(page);
  64         }
  65         end_page_writeback(page);
  66         bio_put(bio);
  67 }
  68
  69 static void swap_slot_free_notify(struct page *page)
  70 {
  71         struct swap_info_struct *sis;
  72         struct gendisk *disk;
  73
  74         /*
  75          * There is no guarantee that the page is in swap cache - the software
  76          * suspend code (at least) uses end_swap_bio_read() against a non-
  77          * swapcache page.  So we must check PG_swapcache before proceeding with
  78          * this optimization.
  79          */
  80         if (unlikely(!PageSwapCache(page)))
  81                 return;
  82
  83         sis = page_swap_info(page);
  84         if (!(sis->flags & SWP_BLKDEV))
  85                 return;
  86
  87         /*
  88          * The swap subsystem performs lazy swap slot freeing,
  89          * expecting that the page will be swapped out again.
  90          * So we can avoid an unnecessary write if the page
  91          * isn't redirtied.
  92          * This is good for real swap storage because we can
  93          * reduce unnecessary I/O and enhance wear-leveling
  94          * if an SSD is used as the as swap device.
  95          * But if in-memory swap device (eg zram) is used,
  96          * this causes a duplicated copy between uncompressed
  97          * data in VM-owned memory and compressed data in
  98          * zram-owned memory.  So let's free zram-owned memory
  99          * and make the VM-owned decompressed page *dirty*,
 100          * so the page should be swapped out somewhere again if
 101          * we again wish to reclaim it.
 102          */
 103         disk = sis->bdev->bd_disk;
 104         if (disk->fops->swap_slot_free_notify) {
 105                 swp_entry_t entry;
 106                 unsigned long offset;
 107
 108                 entry.val = page_private(page);
 109                 offset = swp_offset(entry);
 110
 111                 SetPageDirty(page);
 112                 disk->fops->swap_slot_free_notify(sis->bdev,
 113                                 offset);
 114         }
 115 }
 116
 117 static void end_swap_bio_read(struct bio *bio)
 118 {
 119         struct page *page = bio->bi_io_vec[0].bv_page;
 120
 121         if (bio->bi_error) {
 122                 SetPageError(page);
 123                 ClearPageUptodate(page);
 124                 pr_alert("Read-error on swap-device (%u:%u:%llu)\n",
 125                          imajor(bio->bi_bdev->bd_inode),
 126                          iminor(bio->bi_bdev->bd_inode),
 127                          (unsigned long long)bio->bi_iter.bi_sector);
 128                 goto out;
 129         }
 130
 131         SetPageUptodate(page);
 132         swap_slot_free_notify(page);
 133 out:
 134         unlock_page(page);
 135         bio_put(bio);
 136 }
 137
 138 int generic_swapfile_activate(struct swap_info_struct *sis,
 139                                 struct file *swap_file,
 140                                 sector_t *span)
 141 {
 142         struct address_space *mapping = swap_file->f_mapping;
 143         struct inode *inode = mapping->host;
 144         unsigned blocks_per_page;
 145         unsigned long page_no;
 146         unsigned blkbits;
 147         sector_t probe_block;
 148         sector_t last_block;
 149         sector_t lowest_block = -1;
 150         sector_t highest_block = 0;
 151         int nr_extents = 0;
 152         int ret;
 153
 154         blkbits = inode->i_blkbits;
 155         blocks_per_page = PAGE_SIZE >> blkbits;
 156
 157         /*
 158          * Map all the blocks into the extent list.  This code doesn't try
 159          * to be very smart.
 160          */
 161         probe_block = 0;
 162         page_no = 0;
 163         last_block = i_size_read(inode) >> blkbits;
 164         while ((probe_block + blocks_per_page) <= last_block &&
 165                         page_no < sis->max) {
 166                 unsigned block_in_page;
 167                 sector_t first_block;
 168
 169                 first_block = bmap(inode, probe_block);
 170                 if (first_block == 0)
 171                         goto bad_bmap;
 172
 173                 /*
 174                  * It must be PAGE_SIZE aligned on-disk
 175                  */
 176                 if (first_block & (blocks_per_page - 1)) {
 177                         probe_block++;
 178                         goto reprobe;
 179                 }
 180
 181                 for (block_in_page = 1; block_in_page < blocks_per_page;
 182                                         block_in_page++) {
 183                         sector_t block;
 184
 185                         block = bmap(inode, probe_block + block_in_page);
 186                         if (block == 0)
 187                                 goto bad_bmap;
 188                         if (block != first_block + block_in_page) {
 189                                 /* Discontiguity */
 190                                 probe_block++;
 191                                 goto reprobe;
 192                         }
 193                 }
 194
 195                 first_block >>= (PAGE_SHIFT - blkbits);
 196                 if (page_no) {  /* exclude the header page */
 197                         if (first_block < lowest_block)
 198                                 lowest_block = first_block;
 199                         if (first_block > highest_block)
 200                                 highest_block = first_block;
 201                 }
 202
 203                 /*
 204                  * We found a PAGE_SIZE-length, PAGE_SIZE-aligned run of blocks
 205                  */
 206                 ret = add_swap_extent(sis, page_no, 1, first_block);
 207                 if (ret < 0)
 208                         goto out;
 209                 nr_extents += ret;
 210                 page_no++;
 211                 probe_block += blocks_per_page;
 212 reprobe:
 213                 continue;
 214         }
 215         ret = nr_extents;
 216         *span = 1 + highest_block - lowest_block;
 217         if (page_no == 0)
 218                 page_no = 1;    /* force Empty message */
 219         sis->max = page_no;
 220         sis->pages = page_no - 1;
 221         sis->highest_bit = page_no - 1;
 222 out:
 223         return ret;
 224 bad_bmap:
 225         pr_err("swapon: swapfile has holes\n");
 226         ret = -EINVAL;
 227         goto out;
 228 }
 229
 230 /*
 231  * We may have stale swap cache pages in memory: notice
 232  * them here and get rid of the unnecessary final write.
 233  */
 234 int swap_writepage(struct page *page, struct writeback_control *wbc)
 235 {
 236         int ret = 0;
 237
 238         if (try_to_free_swap(page)) {
 239                 unlock_page(page);
 240                 goto out;
 241         }
 242         if (frontswap_store(page) == 0) {
 243                 set_page_writeback(page);
 244                 unlock_page(page);
 245                 end_page_writeback(page);
 246                 goto out;
 247         }
 248         ret = __swap_writepage(page, wbc, end_swap_bio_write);
 249 out:
 250         return ret;
 251 }
 252
 253 static sector_t swap_page_sector(struct page *page)
 254 {
 255         return (sector_t)__page_file_index(page) << (PAGE_SHIFT - 9);
 256 }
 257
 258 int __swap_writepage(struct page *page, struct writeback_control *wbc,
 259                 bio_end_io_t end_write_func)
 260 {
 261         struct bio *bio;
 262         int ret;
 263         struct swap_info_struct *sis = page_swap_info(page);
 264
 265         if (sis->flags & SWP_FILE) {
 266                 struct kiocb kiocb;
 267                 struct file *swap_file = sis->swap_file;
 268                 struct address_space *mapping = swap_file->f_mapping;
 269                 struct bio_vec bv = {
 270                         .bv_page = page,
 271                         .bv_len  = PAGE_SIZE,
 272                         .bv_offset = 0
 273                 };
 274                 struct iov_iter from;
 275
 276                 iov_iter_bvec(&from, ITER_BVEC | WRITE, &bv, 1, PAGE_SIZE);
 277                 init_sync_kiocb(&kiocb, swap_file);
 278                 kiocb.ki_pos = page_file_offset(page);
 279
 280                 set_page_writeback(page);
 281                 unlock_page(page);
 282                 ret = mapping->a_ops->direct_IO(&kiocb, &from);
 283                 if (ret == PAGE_SIZE) {
 284                         count_vm_event(PSWPOUT);
 285                         ret = 0;
 286                 } else {
 287                         /*
 288                          * In the case of swap-over-nfs, this can be a
 289                          * temporary failure if the system has limited
 290                          * memory for allocating transmit buffers.
 291                          * Mark the page dirty and avoid
 292                          * rotate_reclaimable_page but rate-limit the
 293                          * messages but do not flag PageError like
 294                          * the normal direct-to-bio case as it could
 295                          * be temporary.
 296                          */
 297                         set_page_dirty(page);
 298                         ClearPageReclaim(page);
 299                         pr_err_ratelimited("Write error on dio swapfile (%llu)\n",
 300                                            page_file_offset(page));
 301                 }
 302                 end_page_writeback(page);
 303                 return ret;
 304         }
 305
 306         ret = bdev_write_page(sis->bdev, swap_page_sector(page), page, wbc);
 307         if (!ret) {
 308                 count_vm_event(PSWPOUT);
 309                 return 0;
 310         }
 311
 312         ret = 0;
 313         bio = get_swap_bio(GFP_NOIO, page, end_write_func);
 314         if (bio == NULL) {
 315                 set_page_dirty(page);
 316                 unlock_page(page);
 317                 ret = -ENOMEM;
 318                 goto out;
 319         }
 320         bio_set_op_attrs(bio, REQ_OP_WRITE, 0);
 321         if (wbc->sync_mode == WB_SYNC_ALL)
 322                 bio->bi_rw |= REQ_SYNC;
 323         count_vm_event(PSWPOUT);
 324         set_page_writeback(page);
 325         unlock_page(page);
 326         submit_bio(bio);
 327 out:
 328         return ret;
 329 }
 330
 331 int swap_readpage(struct page *page)
 332 {
 333         struct bio *bio;
 334         int ret = 0;
 335         struct swap_info_struct *sis = page_swap_info(page);
 336
 337         VM_BUG_ON_PAGE(!PageLocked(page), page);
 338         VM_BUG_ON_PAGE(PageUptodate(page), page);
 339         if (frontswap_load(page) == 0) {
 340                 SetPageUptodate(page);
 341                 unlock_page(page);
 342                 goto out;
 343         }
 344
 345         if (sis->flags & SWP_FILE) {
 346                 struct file *swap_file = sis->swap_file;
 347                 struct address_space *mapping = swap_file->f_mapping;
 348
 349                 ret = mapping->a_ops->readpage(swap_file, page);
 350                 if (!ret)
 351                         count_vm_event(PSWPIN);
 352                 return ret;
 353         }
 354
 355         ret = bdev_read_page(sis->bdev, swap_page_sector(page), page);
 356         if (!ret) {
 357                 if (trylock_page(page)) {
 358                         swap_slot_free_notify(page);
 359                         unlock_page(page);
 360                 }
 361
 362                 count_vm_event(PSWPIN);
 363                 return 0;
 364         }
 365
 366         ret = 0;
 367         bio = get_swap_bio(GFP_KERNEL, page, end_swap_bio_read);
 368         if (bio == NULL) {
 369                 unlock_page(page);
 370                 ret = -ENOMEM;
 371                 goto out;
 372         }
 373         bio_set_op_attrs(bio, REQ_OP_READ, 0);
 374         count_vm_event(PSWPIN);
 375         submit_bio(bio);
 376 out:
 377         return ret;
 378 }
 379
 380 int swap_set_page_dirty(struct page *page)
 381 {
 382         struct swap_info_struct *sis = page_swap_info(page);
 383
 384         if (sis->flags & SWP_FILE) {
 385                 struct address_space *mapping = sis->swap_file->f_mapping;
 386                 return mapping->a_ops->set_page_dirty(page);
 387         } else {
 388                 return __set_page_dirty_no_writeback(page);
 389         }
 390 }