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/psi.h>
  26 #include <linux/uio.h>
  27 #include <linux/sched/task.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         struct bio *bio;
  33
  34         bio = bio_alloc(gfp_flags, 1);
  35         if (bio) {
  36                 struct block_device *bdev;
  37
  38                 bio->bi_iter.bi_sector = map_swap_page(page, &bdev);
  39                 bio_set_dev(bio, bdev);
  40                 bio->bi_iter.bi_sector <<= PAGE_SHIFT - 9;
  41                 bio->bi_end_io = end_io;
  42
  43                 bio_add_page(bio, page, PAGE_SIZE * hpage_nr_pages(page), 0);
  44         }
  45         return bio;
  46 }
  47
  48 void end_swap_bio_write(struct bio *bio)
  49 {
  50         struct page *page = bio_first_page_all(bio);
  51
  52         if (bio->bi_status) {
  53                 SetPageError(page);
  54                 /*
  55                  * We failed to write the page out to swap-space.
  56                  * Re-dirty the page in order to avoid it being reclaimed.
  57                  * Also print a dire warning that things will go BAD (tm)
  58                  * very quickly.
  59                  *
  60                  * Also clear PG_reclaim to avoid rotate_reclaimable_page()
  61                  */
  62                 set_page_dirty(page);
  63                 pr_alert("Write-error on swap-device (%u:%u:%llu)\n",
  64                          MAJOR(bio_dev(bio)), MINOR(bio_dev(bio)),
  65                          (unsigned long long)bio->bi_iter.bi_sector);
  66                 ClearPageReclaim(page);
  67         }
  68         end_page_writeback(page);
  69         bio_put(bio);
  70 }
  71
  72 static void swap_slot_free_notify(struct page *page)
  73 {
  74         struct swap_info_struct *sis;
  75         struct gendisk *disk;
  76         swp_entry_t entry;
  77
  78         /*
  79          * There is no guarantee that the page is in swap cache - the software
  80          * suspend code (at least) uses end_swap_bio_read() against a non-
  81          * swapcache page.  So we must check PG_swapcache before proceeding with
  82          * this optimization.
  83          */
  84         if (unlikely(!PageSwapCache(page)))
  85                 return;
  86
  87         sis = page_swap_info(page);
  88         if (!(sis->flags & SWP_BLKDEV))
  89                 return;
  90
  91         /*
  92          * The swap subsystem performs lazy swap slot freeing,
  93          * expecting that the page will be swapped out again.
  94          * So we can avoid an unnecessary write if the page
  95          * isn't redirtied.
  96          * This is good for real swap storage because we can
  97          * reduce unnecessary I/O and enhance wear-leveling
  98          * if an SSD is used as the as swap device.
  99          * But if in-memory swap device (eg zram) is used,
 100          * this causes a duplicated copy between uncompressed
 101          * data in VM-owned memory and compressed data in
 102          * zram-owned memory.  So let's free zram-owned memory
 103          * and make the VM-owned decompressed page *dirty*,
 104          * so the page should be swapped out somewhere again if
 105          * we again wish to reclaim it.
 106          */
 107         disk = sis->bdev->bd_disk;
 108         entry.val = page_private(page);
 109         if (disk->fops->swap_slot_free_notify && __swap_count(entry) == 1) {
 110                 unsigned long offset;
 111
 112                 offset = swp_offset(entry);
 113
 114                 SetPageDirty(page);
 115                 disk->fops->swap_slot_free_notify(sis->bdev,
 116                                 offset);
 117         }
 118 }
 119
 120 static void end_swap_bio_read(struct bio *bio)
 121 {
 122         struct page *page = bio_first_page_all(bio);
 123         struct task_struct *waiter = bio->bi_private;
 124
 125         if (bio->bi_status) {
 126                 SetPageError(page);
 127                 ClearPageUptodate(page);
 128                 pr_alert("Read-error on swap-device (%u:%u:%llu)\n",
 129                          MAJOR(bio_dev(bio)), MINOR(bio_dev(bio)),
 130                          (unsigned long long)bio->bi_iter.bi_sector);
 131                 goto out;
 132         }
 133
 134         SetPageUptodate(page);
 135         swap_slot_free_notify(page);
 136 out:
 137         unlock_page(page);
 138         WRITE_ONCE(bio->bi_private, NULL);
 139         bio_put(bio);
 140         if (waiter) {
 141                 blk_wake_io_task(waiter);
 142                 put_task_struct(waiter);
 143         }
 144 }
 145
 146 int generic_swapfile_activate(struct swap_info_struct *sis,
 147                                 struct file *swap_file,
 148                                 sector_t *span)
 149 {
 150         struct address_space *mapping = swap_file->f_mapping;
 151         struct inode *inode = mapping->host;
 152         unsigned blocks_per_page;
 153         unsigned long page_no;
 154         unsigned blkbits;
 155         sector_t probe_block;
 156         sector_t last_block;
 157         sector_t lowest_block = -1;
 158         sector_t highest_block = 0;
 159         int nr_extents = 0;
 160         int ret;
 161
 162         blkbits = inode->i_blkbits;
 163         blocks_per_page = PAGE_SIZE >> blkbits;
 164
 165         /*
 166          * Map all the blocks into the extent tree.  This code doesn't try
 167          * to be very smart.
 168          */
 169         probe_block = 0;
 170         page_no = 0;
 171         last_block = i_size_read(inode) >> blkbits;
 172         while ((probe_block + blocks_per_page) <= last_block &&
 173                         page_no < sis->max) {
 174                 unsigned block_in_page;
 175                 sector_t first_block;
 176
 177                 cond_resched();
 178
 179                 first_block = probe_block;
 180                 ret = bmap(inode, &first_block);
 181                 if (ret || !first_block)
 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 = probe_block + block_in_page;
 197                         ret = bmap(inode, &block);
 198                         if (ret || !block)
 199                                 goto bad_bmap;
 200
 201                         if (block != first_block + block_in_page) {
 202                                 /* Discontiguity */
 203                                 probe_block++;
 204                                 goto reprobe;
 205                         }
 206                 }
 207
 208                 first_block >>= (PAGE_SHIFT - blkbits);
 209                 if (page_no) {  /* exclude the header page */
 210                         if (first_block < lowest_block)
 211                                 lowest_block = first_block;
 212                         if (first_block > highest_block)
 213                                 highest_block = first_block;
 214                 }
 215
 216                 /*
 217                  * We found a PAGE_SIZE-length, PAGE_SIZE-aligned run of blocks
 218                  */
 219                 ret = add_swap_extent(sis, page_no, 1, first_block);
 220                 if (ret < 0)
 221                         goto out;
 222                 nr_extents += ret;
 223                 page_no++;
 224                 probe_block += blocks_per_page;
 225 reprobe:
 226                 continue;
 227         }
 228         ret = nr_extents;
 229         *span = 1 + highest_block - lowest_block;
 230         if (page_no == 0)
 231                 page_no = 1;    /* force Empty message */
 232         sis->max = page_no;
 233         sis->pages = page_no - 1;
 234         sis->highest_bit = page_no - 1;
 235 out:
 236         return ret;
 237 bad_bmap:
 238         pr_err("swapon: swapfile has holes\n");
 239         ret = -EINVAL;
 240         goto out;
 241 }
 242
 243 /*
 244  * We may have stale swap cache pages in memory: notice
 245  * them here and get rid of the unnecessary final write.
 246  */
 247 int swap_writepage(struct page *page, struct writeback_control *wbc)
 248 {
 249         int ret = 0;
 250
 251         if (try_to_free_swap(page)) {
 252                 unlock_page(page);
 253                 goto out;
 254         }
 255         if (frontswap_store(page) == 0) {
 256                 set_page_writeback(page);
 257                 unlock_page(page);
 258                 end_page_writeback(page);
 259                 goto out;
 260         }
 261         ret = __swap_writepage(page, wbc, end_swap_bio_write);
 262 out:
 263         return ret;
 264 }
 265
 266 static sector_t swap_page_sector(struct page *page)
 267 {
 268         return (sector_t)__page_file_index(page) << (PAGE_SHIFT - 9);
 269 }
 270
 271 static inline void count_swpout_vm_event(struct page *page)
 272 {
 273 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 274         if (unlikely(PageTransHuge(page)))
 275                 count_vm_event(THP_SWPOUT);
 276 #endif
 277         count_vm_events(PSWPOUT, hpage_nr_pages(page));
 278 }
 279
 280 int __swap_writepage(struct page *page, struct writeback_control *wbc,
 281                 bio_end_io_t end_write_func)
 282 {
 283         struct bio *bio;
 284         int ret;
 285         struct swap_info_struct *sis = page_swap_info(page);
 286
 287         VM_BUG_ON_PAGE(!PageSwapCache(page), page);
 288         if (sis->flags & SWP_FS) {
 289                 struct kiocb kiocb;
 290                 struct file *swap_file = sis->swap_file;
 291                 struct address_space *mapping = swap_file->f_mapping;
 292                 struct bio_vec bv = {
 293                         .bv_page = page,
 294                         .bv_len  = PAGE_SIZE,
 295                         .bv_offset = 0
 296                 };
 297                 struct iov_iter from;
 298
 299                 iov_iter_bvec(&from, WRITE, &bv, 1, PAGE_SIZE);
 300                 init_sync_kiocb(&kiocb, swap_file);
 301                 kiocb.ki_pos = page_file_offset(page);
 302
 303                 set_page_writeback(page);
 304                 unlock_page(page);
 305                 ret = mapping->a_ops->direct_IO(&kiocb, &from);
 306                 if (ret == PAGE_SIZE) {
 307                         count_vm_event(PSWPOUT);
 308                         ret = 0;
 309                 } else {
 310                         /*
 311                          * In the case of swap-over-nfs, this can be a
 312                          * temporary failure if the system has limited
 313                          * memory for allocating transmit buffers.
 314                          * Mark the page dirty and avoid
 315                          * rotate_reclaimable_page but rate-limit the
 316                          * messages but do not flag PageError like
 317                          * the normal direct-to-bio case as it could
 318                          * be temporary.
 319                          */
 320                         set_page_dirty(page);
 321                         ClearPageReclaim(page);
 322                         pr_err_ratelimited("Write error on dio swapfile (%llu)\n",
 323                                            page_file_offset(page));
 324                 }
 325                 end_page_writeback(page);
 326                 return ret;
 327         }
 328
 329         ret = bdev_write_page(sis->bdev, swap_page_sector(page), page, wbc);
 330         if (!ret) {
 331                 count_swpout_vm_event(page);
 332                 return 0;
 333         }
 334
 335         ret = 0;
 336         bio = get_swap_bio(GFP_NOIO, page, end_write_func);
 337         if (bio == NULL) {
 338                 set_page_dirty(page);
 339                 unlock_page(page);
 340                 ret = -ENOMEM;
 341                 goto out;
 342         }
 343         bio->bi_opf = REQ_OP_WRITE | REQ_SWAP | wbc_to_write_flags(wbc);
 344         bio_associate_blkg_from_page(bio, page);
 345         count_swpout_vm_event(page);
 346         set_page_writeback(page);
 347         unlock_page(page);
 348         submit_bio(bio);
 349 out:
 350         return ret;
 351 }
 352
 353 int swap_readpage(struct page *page, bool synchronous)
 354 {
 355         struct bio *bio;
 356         int ret = 0;
 357         struct swap_info_struct *sis = page_swap_info(page);
 358         blk_qc_t qc;
 359         struct gendisk *disk;
 360         unsigned long pflags;
 361
 362         VM_BUG_ON_PAGE(!PageSwapCache(page) && !synchronous, page);
 363         VM_BUG_ON_PAGE(!PageLocked(page), page);
 364         VM_BUG_ON_PAGE(PageUptodate(page), page);
 365
 366         /*
 367          * Count submission time as memory stall. When the device is congested,
 368          * or the submitting cgroup IO-throttled, submission can be a
 369          * significant part of overall IO time.
 370          */
 371         psi_memstall_enter(&pflags);
 372
 373         if (frontswap_load(page) == 0) {
 374                 SetPageUptodate(page);
 375                 unlock_page(page);
 376                 goto out;
 377         }
 378
 379         if (sis->flags & SWP_FS) {
 380                 struct file *swap_file = sis->swap_file;
 381                 struct address_space *mapping = swap_file->f_mapping;
 382
 383                 ret = mapping->a_ops->readpage(swap_file, page);
 384                 if (!ret)
 385                         count_vm_event(PSWPIN);
 386                 goto out;
 387         }
 388
 389         ret = bdev_read_page(sis->bdev, swap_page_sector(page), page);
 390         if (!ret) {
 391                 if (trylock_page(page)) {
 392                         swap_slot_free_notify(page);
 393                         unlock_page(page);
 394                 }
 395
 396                 count_vm_event(PSWPIN);
 397                 goto out;
 398         }
 399
 400         ret = 0;
 401         bio = get_swap_bio(GFP_KERNEL, page, end_swap_bio_read);
 402         if (bio == NULL) {
 403                 unlock_page(page);
 404                 ret = -ENOMEM;
 405                 goto out;
 406         }
 407         disk = bio->bi_disk;
 408         /*
 409          * Keep this task valid during swap readpage because the oom killer may
 410          * attempt to access it in the page fault retry time check.
 411          */
 412         bio_set_op_attrs(bio, REQ_OP_READ, 0);
 413         if (synchronous) {
 414                 bio->bi_opf |= REQ_HIPRI;
 415                 get_task_struct(current);
 416                 bio->bi_private = current;
 417         }
 418         count_vm_event(PSWPIN);
 419         bio_get(bio);
 420         qc = submit_bio(bio);
 421         while (synchronous) {
 422                 set_current_state(TASK_UNINTERRUPTIBLE);
 423                 if (!READ_ONCE(bio->bi_private))
 424                         break;
 425
 426                 if (!blk_poll(disk->queue, qc, true))
 427                         io_schedule();
 428         }
 429         __set_current_state(TASK_RUNNING);
 430         bio_put(bio);
 431
 432 out:
 433         psi_memstall_leave(&pflags);
 434         return ret;
 435 }
 436
 437 int swap_set_page_dirty(struct page *page)
 438 {
 439         struct swap_info_struct *sis = page_swap_info(page);
 440
 441         if (sis->flags & SWP_FS) {
 442                 struct address_space *mapping = sis->swap_file->f_mapping;
 443
 444                 VM_BUG_ON_PAGE(!PageSwapCache(page), page);
 445                 return mapping->a_ops->set_page_dirty(page);
 446         } else {
 447                 return __set_page_dirty_no_writeback(page);
 448         }
 449 }