mm/page_io.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  *  linux/mm/page_io.c
   4  *
   5  *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
   6  *
   7  *  Swap reorganised 29.12.95,
   8  *  Asynchronous swapping added 30.12.95. Stephen Tweedie
   9  *  Removed race in async swapping. 14.4.1996. Bruno Haible
  10  *  Add swap of shared pages through the page cache. 20.2.1998. Stephen Tweedie
  11  *  Always use brw_page, life becomes simpler. 12 May 1998 Eric Biederman
  12  */
  13
  14 #include <linux/mm.h>
  15 #include <linux/kernel_stat.h>
  16 #include <linux/gfp.h>
  17 #include <linux/pagemap.h>
  18 #include <linux/swap.h>
  19 #include <linux/bio.h>
  20 #include <linux/swapops.h>
  21 #include <linux/buffer_head.h>
  22 #include <linux/writeback.h>
  23 #include <linux/frontswap.h>
  24 #include <linux/blkdev.h>
  25 #include <linux/uio.h>
  26 #include <linux/sched/task.h>
  27 #include <asm/pgtable.h>
  28
  29 static struct bio *get_swap_bio(gfp_t gfp_flags,
  30                                 struct page *page, bio_end_io_t end_io)
  31 {
  32         int i, nr = hpage_nr_pages(page);
  33         struct bio *bio;
  34
  35         bio = bio_alloc(gfp_flags, nr);
  36         if (bio) {
  37                 struct block_device *bdev;
  38
  39                 bio->bi_iter.bi_sector = map_swap_page(page, &bdev);
  40                 bio_set_dev(bio, bdev);
  41                 bio->bi_end_io = end_io;
  42
  43                 for (i = 0; i < nr; i++)
  44                         bio_add_page(bio, page + i, PAGE_SIZE, 0);
  45                 VM_BUG_ON(bio->bi_iter.bi_size != PAGE_SIZE * nr);
  46         }
  47         return bio;
  48 }
  49
  50 void end_swap_bio_write(struct bio *bio)
  51 {
  52         struct page *page = bio_first_page_all(bio);
  53
  54         if (bio->bi_status) {
  55                 SetPageError(page);
  56                 /*
  57                  * We failed to write the page out to swap-space.
  58                  * Re-dirty the page in order to avoid it being reclaimed.
  59                  * Also print a dire warning that things will go BAD (tm)
  60                  * very quickly.
  61                  *
  62                  * Also clear PG_reclaim to avoid rotate_reclaimable_page()
  63                  */
  64                 set_page_dirty(page);
  65                 pr_alert("Write-error on swap-device (%u:%u:%llu)\n",
  66                          MAJOR(bio_dev(bio)), MINOR(bio_dev(bio)),
  67                          (unsigned long long)bio->bi_iter.bi_sector);
  68                 ClearPageReclaim(page);
  69         }
  70         end_page_writeback(page);
  71         bio_put(bio);
  72 }
  73
  74 static void swap_slot_free_notify(struct page *page)
  75 {
  76         struct swap_info_struct *sis;
  77         struct gendisk *disk;
  78         swp_entry_t entry;
  79
  80         /*
  81          * There is no guarantee that the page is in swap cache - the software
  82          * suspend code (at least) uses end_swap_bio_read() against a non-
  83          * swapcache page.  So we must check PG_swapcache before proceeding with
  84          * this optimization.
  85          */
  86         if (unlikely(!PageSwapCache(page)))
  87                 return;
  88
  89         sis = page_swap_info(page);
  90         if (!(sis->flags & SWP_BLKDEV))
  91                 return;
  92
  93         /*
  94          * The swap subsystem performs lazy swap slot freeing,
  95          * expecting that the page will be swapped out again.
  96          * So we can avoid an unnecessary write if the page
  97          * isn't redirtied.
  98          * This is good for real swap storage because we can
  99          * reduce unnecessary I/O and enhance wear-leveling
 100          * if an SSD is used as the as swap device.
 101          * But if in-memory swap device (eg zram) is used,
 102          * this causes a duplicated copy between uncompressed
 103          * data in VM-owned memory and compressed data in
 104          * zram-owned memory.  So let's free zram-owned memory
 105          * and make the VM-owned decompressed page *dirty*,
 106          * so the page should be swapped out somewhere again if
 107          * we again wish to reclaim it.
 108          */
 109         disk = sis->bdev->bd_disk;
 110         entry.val = page_private(page);
 111         if (disk->fops->swap_slot_free_notify &&
 112                         __swap_count(sis, entry) == 1) {
 113                 unsigned long offset;
 114
 115                 offset = swp_offset(entry);
 116
 117                 SetPageDirty(page);
 118                 disk->fops->swap_slot_free_notify(sis->bdev,
 119                                 offset);
 120         }
 121 }
 122
 123 static void end_swap_bio_read(struct bio *bio)
 124 {
 125         struct page *page = bio_first_page_all(bio);
 126         struct task_struct *waiter = bio->bi_private;
 127
 128         if (bio->bi_status) {
 129                 SetPageError(page);
 130                 ClearPageUptodate(page);
 131                 pr_alert("Read-error on swap-device (%u:%u:%llu)\n",
 132                          MAJOR(bio_dev(bio)), MINOR(bio_dev(bio)),
 133                          (unsigned long long)bio->bi_iter.bi_sector);
 134                 goto out;
 135         }
 136
 137         SetPageUptodate(page);
 138         swap_slot_free_notify(page);
 139 out:
 140         unlock_page(page);
 141         WRITE_ONCE(bio->bi_private, NULL);
 142         bio_put(bio);
 143         wake_up_process(waiter);
 144         put_task_struct(waiter);
 145 }
 146
 147 int generic_swapfile_activate(struct swap_info_struct *sis,
 148                                 struct file *swap_file,
 149                                 sector_t *span)
 150 {
 151         struct address_space *mapping = swap_file->f_mapping;
 152         struct inode *inode = mapping->host;
 153         unsigned blocks_per_page;
 154         unsigned long page_no;
 155         unsigned blkbits;
 156         sector_t probe_block;
 157         sector_t last_block;
 158         sector_t lowest_block = -1;
 159         sector_t highest_block = 0;
 160         int nr_extents = 0;
 161         int ret;
 162
 163         blkbits = inode->i_blkbits;
 164         blocks_per_page = PAGE_SIZE >> blkbits;
 165
 166         /*
 167          * Map all the blocks into the extent list.  This code doesn't try
 168          * to be very smart.
 169          */
 170         probe_block = 0;
 171         page_no = 0;
 172         last_block = i_size_read(inode) >> blkbits;
 173         while ((probe_block + blocks_per_page) <= last_block &&
 174                         page_no < sis->max) {
 175                 unsigned block_in_page;
 176                 sector_t first_block;
 177
 178                 cond_resched();
 179
 180                 first_block = bmap(inode, probe_block);
 181                 if (first_block == 0)
 182                         goto bad_bmap;
 183
 184                 /*
 185                  * It must be PAGE_SIZE aligned on-disk
 186                  */
 187                 if (first_block & (blocks_per_page - 1)) {
 188                         probe_block++;
 189                         goto reprobe;
 190                 }
 191
 192                 for (block_in_page = 1; block_in_page < blocks_per_page;
 193                                         block_in_page++) {
 194                         sector_t block;
 195
 196                         block = bmap(inode, probe_block + block_in_page);
 197                         if (block == 0)
 198                                 goto bad_bmap;
 199                         if (block != first_block + block_in_page) {
 200                                 /* Discontiguity */
 201                                 probe_block++;
 202                                 goto reprobe;
 203                         }
 204                 }
 205
 206                 first_block >>= (PAGE_SHIFT - blkbits);
 207                 if (page_no) {  /* exclude the header page */
 208                         if (first_block < lowest_block)
 209                                 lowest_block = first_block;
 210                         if (first_block > highest_block)
 211                                 highest_block = first_block;
 212                 }
 213
 214                 /*
 215                  * We found a PAGE_SIZE-length, PAGE_SIZE-aligned run of blocks
 216                  */
 217                 ret = add_swap_extent(sis, page_no, 1, first_block);
 218                 if (ret < 0)
 219                         goto out;
 220                 nr_extents += ret;
 221                 page_no++;
 222                 probe_block += blocks_per_page;
 223 reprobe:
 224                 continue;
 225         }
 226         ret = nr_extents;
 227         *span = 1 + highest_block - lowest_block;
 228         if (page_no == 0)
 229                 page_no = 1;    /* force Empty message */
 230         sis->max = page_no;
 231         sis->pages = page_no - 1;
 232         sis->highest_bit = page_no - 1;
 233 out:
 234         return ret;
 235 bad_bmap:
 236         pr_err("swapon: swapfile has holes\n");
 237         ret = -EINVAL;
 238         goto out;
 239 }
 240
 241 /*
 242  * We may have stale swap cache pages in memory: notice
 243  * them here and get rid of the unnecessary final write.
 244  */
 245 int swap_writepage(struct page *page, struct writeback_control *wbc)
 246 {
 247         int ret = 0;
 248
 249         if (try_to_free_swap(page)) {
 250                 unlock_page(page);
 251                 goto out;
 252         }
 253         if (frontswap_store(page) == 0) {
 254                 set_page_writeback(page);
 255                 unlock_page(page);
 256                 end_page_writeback(page);
 257                 goto out;
 258         }
 259         ret = __swap_writepage(page, wbc, end_swap_bio_write);
 260 out:
 261         return ret;
 262 }
 263
 264 static inline void count_swpout_vm_event(struct page *page)
 265 {
 266 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 267         if (unlikely(PageTransHuge(page)))
 268                 count_vm_event(THP_SWPOUT);
 269 #endif
 270         count_vm_events(PSWPOUT, hpage_nr_pages(page));
 271 }
 272
 273 int __swap_writepage(struct page *page, struct writeback_control *wbc,
 274                 bio_end_io_t end_write_func)
 275 {
 276         struct bio *bio;
 277         int ret;
 278         struct swap_info_struct *sis = page_swap_info(page);
 279
 280         VM_BUG_ON_PAGE(!PageSwapCache(page), page);
 281         if (sis->flags & SWP_FILE) {
 282                 struct kiocb kiocb;
 283                 struct file *swap_file = sis->swap_file;
 284                 struct address_space *mapping = swap_file->f_mapping;
 285                 struct bio_vec bv = {
 286                         .bv_page = page,
 287                         .bv_len  = PAGE_SIZE,
 288                         .bv_offset = 0
 289                 };
 290                 struct iov_iter from;
 291
 292                 iov_iter_bvec(&from, ITER_BVEC | WRITE, &bv, 1, PAGE_SIZE);
 293                 init_sync_kiocb(&kiocb, swap_file);
 294                 kiocb.ki_pos = page_file_offset(page);
 295
 296                 set_page_writeback(page);
 297                 unlock_page(page);
 298                 ret = mapping->a_ops->direct_IO(&kiocb, &from);
 299                 if (ret == PAGE_SIZE) {
 300                         count_vm_event(PSWPOUT);
 301                         ret = 0;
 302                 } else {
 303                         /*
 304                          * In the case of swap-over-nfs, this can be a
 305                          * temporary failure if the system has limited
 306                          * memory for allocating transmit buffers.
 307                          * Mark the page dirty and avoid
 308                          * rotate_reclaimable_page but rate-limit the
 309                          * messages but do not flag PageError like
 310                          * the normal direct-to-bio case as it could
 311                          * be temporary.
 312                          */
 313                         set_page_dirty(page);
 314                         ClearPageReclaim(page);
 315                         pr_err_ratelimited("Write error on dio swapfile (%llu)\n",
 316                                            page_file_offset(page));
 317                 }
 318                 end_page_writeback(page);
 319                 return ret;
 320         }
 321
 322         ret = bdev_write_page(sis->bdev, map_swap_page(page, &sis->bdev),
 323                               page, wbc);
 324         if (!ret) {
 325                 count_swpout_vm_event(page);
 326                 return 0;
 327         }
 328
 329         ret = 0;
 330         bio = get_swap_bio(GFP_NOIO, page, end_write_func);
 331         if (bio == NULL) {
 332                 set_page_dirty(page);
 333                 unlock_page(page);
 334                 ret = -ENOMEM;
 335                 goto out;
 336         }
 337         bio->bi_opf = REQ_OP_WRITE | REQ_SWAP | wbc_to_write_flags(wbc);
 338         bio_associate_blkcg_from_page(bio, page);
 339         count_swpout_vm_event(page);
 340         set_page_writeback(page);
 341         unlock_page(page);
 342         submit_bio(bio);
 343 out:
 344         return ret;
 345 }
 346
 347 int swap_readpage(struct page *page, bool synchronous)
 348 {
 349         struct bio *bio;
 350         int ret = 0;
 351         struct swap_info_struct *sis = page_swap_info(page);
 352         blk_qc_t qc;
 353         struct gendisk *disk;
 354
 355         VM_BUG_ON_PAGE(!PageSwapCache(page) && !synchronous, page);
 356         VM_BUG_ON_PAGE(!PageLocked(page), page);
 357         VM_BUG_ON_PAGE(PageUptodate(page), page);
 358         if (frontswap_load(page) == 0) {
 359                 SetPageUptodate(page);
 360                 unlock_page(page);
 361                 goto out;
 362         }
 363
 364         if (sis->flags & SWP_FILE) {
 365                 struct file *swap_file = sis->swap_file;
 366                 struct address_space *mapping = swap_file->f_mapping;
 367
 368                 ret = mapping->a_ops->readpage(swap_file, page);
 369                 if (!ret)
 370                         count_vm_event(PSWPIN);
 371                 return ret;
 372         }
 373
 374         ret = bdev_read_page(sis->bdev, map_swap_page(page, &sis->bdev), page);
 375         if (!ret) {
 376                 if (trylock_page(page)) {
 377                         swap_slot_free_notify(page);
 378                         unlock_page(page);
 379                 }
 380
 381                 count_vm_event(PSWPIN);
 382                 return 0;
 383         }
 384
 385         ret = 0;
 386         bio = get_swap_bio(GFP_KERNEL, page, end_swap_bio_read);
 387         if (bio == NULL) {
 388                 unlock_page(page);
 389                 ret = -ENOMEM;
 390                 goto out;
 391         }
 392         disk = bio->bi_disk;
 393         /*
 394          * Keep this task valid during swap readpage because the oom killer may
 395          * attempt to access it in the page fault retry time check.
 396          */
 397         get_task_struct(current);
 398         bio->bi_private = current;
 399         bio_set_op_attrs(bio, REQ_OP_READ, 0);
 400         count_vm_event(PSWPIN);
 401         bio_get(bio);
 402         qc = submit_bio(bio);
 403         while (synchronous) {
 404                 set_current_state(TASK_UNINTERRUPTIBLE);
 405                 if (!READ_ONCE(bio->bi_private))
 406                         break;
 407
 408                 if (!blk_poll(disk->queue, qc))
 409                         break;
 410         }
 411         __set_current_state(TASK_RUNNING);
 412         bio_put(bio);
 413
 414 out:
 415         return ret;
 416 }
 417
 418 int swap_set_page_dirty(struct page *page)
 419 {
 420         struct swap_info_struct *sis = page_swap_info(page);
 421
 422         if (sis->flags & SWP_FILE) {
 423                 struct address_space *mapping = sis->swap_file->f_mapping;
 424
 425                 VM_BUG_ON_PAGE(!PageSwapCache(page), page);
 426                 return mapping->a_ops->set_page_dirty(page);
 427         } else {
 428                 return __set_page_dirty_no_writeback(page);
 429         }
 430 }