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_iter.bi_sector <<= PAGE_SHIFT - 9; 42 bio->bi_end_io = end_io; 43 44 for (i = 0; i < nr; i++) 45 bio_add_page(bio, page + i, PAGE_SIZE, 0); 46 VM_BUG_ON(bio->bi_iter.bi_size != PAGE_SIZE * nr); 47 } 48 return bio; 49 } 50 51 void end_swap_bio_write(struct bio *bio) 52 { 53 struct page *page = bio_first_page_all(bio); 54 55 if (bio->bi_status) { 56 SetPageError(page); 57 /* 58 * We failed to write the page out to swap-space. 59 * Re-dirty the page in order to avoid it being reclaimed. 60 * Also print a dire warning that things will go BAD (tm) 61 * very quickly. 62 * 63 * Also clear PG_reclaim to avoid rotate_reclaimable_page() 64 */ 65 set_page_dirty(page); 66 pr_alert("Write-error on swap-device (%u:%u:%llu)\n", 67 MAJOR(bio_dev(bio)), MINOR(bio_dev(bio)), 68 (unsigned long long)bio->bi_iter.bi_sector); 69 ClearPageReclaim(page); 70 } 71 end_page_writeback(page); 72 bio_put(bio); 73 } 74 75 static void swap_slot_free_notify(struct page *page) 76 { 77 struct swap_info_struct *sis; 78 struct gendisk *disk; 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 if (disk->fops->swap_slot_free_notify) { 111 swp_entry_t entry; 112 unsigned long offset; 113 114 entry.val = page_private(page); 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 sector_t swap_page_sector(struct page *page) 265 { 266 return (sector_t)__page_file_index(page) << (PAGE_SHIFT - 9); 267 } 268 269 static inline void count_swpout_vm_event(struct page *page) 270 { 271 #ifdef CONFIG_TRANSPARENT_HUGEPAGE 272 if (unlikely(PageTransHuge(page))) 273 count_vm_event(THP_SWPOUT); 274 #endif 275 count_vm_events(PSWPOUT, hpage_nr_pages(page)); 276 } 277 278 int __swap_writepage(struct page *page, struct writeback_control *wbc, 279 bio_end_io_t end_write_func) 280 { 281 struct bio *bio; 282 int ret; 283 struct swap_info_struct *sis = page_swap_info(page); 284 285 VM_BUG_ON_PAGE(!PageSwapCache(page), page); 286 if (sis->flags & SWP_FILE) { 287 struct kiocb kiocb; 288 struct file *swap_file = sis->swap_file; 289 struct address_space *mapping = swap_file->f_mapping; 290 struct bio_vec bv = { 291 .bv_page = page, 292 .bv_len = PAGE_SIZE, 293 .bv_offset = 0 294 }; 295 struct iov_iter from; 296 297 iov_iter_bvec(&from, ITER_BVEC | WRITE, &bv, 1, PAGE_SIZE); 298 init_sync_kiocb(&kiocb, swap_file); 299 kiocb.ki_pos = page_file_offset(page); 300 301 set_page_writeback(page); 302 unlock_page(page); 303 ret = mapping->a_ops->direct_IO(&kiocb, &from); 304 if (ret == PAGE_SIZE) { 305 count_vm_event(PSWPOUT); 306 ret = 0; 307 } else { 308 /* 309 * In the case of swap-over-nfs, this can be a 310 * temporary failure if the system has limited 311 * memory for allocating transmit buffers. 312 * Mark the page dirty and avoid 313 * rotate_reclaimable_page but rate-limit the 314 * messages but do not flag PageError like 315 * the normal direct-to-bio case as it could 316 * be temporary. 317 */ 318 set_page_dirty(page); 319 ClearPageReclaim(page); 320 pr_err_ratelimited("Write error on dio swapfile (%llu)\n", 321 page_file_offset(page)); 322 } 323 end_page_writeback(page); 324 return ret; 325 } 326 327 ret = bdev_write_page(sis->bdev, swap_page_sector(page), page, wbc); 328 if (!ret) { 329 count_swpout_vm_event(page); 330 return 0; 331 } 332 333 ret = 0; 334 bio = get_swap_bio(GFP_NOIO, page, end_write_func); 335 if (bio == NULL) { 336 set_page_dirty(page); 337 unlock_page(page); 338 ret = -ENOMEM; 339 goto out; 340 } 341 bio->bi_opf = REQ_OP_WRITE | wbc_to_write_flags(wbc); 342 count_swpout_vm_event(page); 343 set_page_writeback(page); 344 unlock_page(page); 345 submit_bio(bio); 346 out: 347 return ret; 348 } 349 350 int swap_readpage(struct page *page, bool synchronous) 351 { 352 struct bio *bio; 353 int ret = 0; 354 struct swap_info_struct *sis = page_swap_info(page); 355 blk_qc_t qc; 356 struct gendisk *disk; 357 358 VM_BUG_ON_PAGE(!PageSwapCache(page) && !synchronous, page); 359 VM_BUG_ON_PAGE(!PageLocked(page), page); 360 VM_BUG_ON_PAGE(PageUptodate(page), page); 361 if (frontswap_load(page) == 0) { 362 SetPageUptodate(page); 363 unlock_page(page); 364 goto out; 365 } 366 367 if (sis->flags & SWP_FILE) { 368 struct file *swap_file = sis->swap_file; 369 struct address_space *mapping = swap_file->f_mapping; 370 371 ret = mapping->a_ops->readpage(swap_file, page); 372 if (!ret) 373 count_vm_event(PSWPIN); 374 return ret; 375 } 376 377 ret = bdev_read_page(sis->bdev, swap_page_sector(page), page); 378 if (!ret) { 379 if (trylock_page(page)) { 380 swap_slot_free_notify(page); 381 unlock_page(page); 382 } 383 384 count_vm_event(PSWPIN); 385 return 0; 386 } 387 388 ret = 0; 389 bio = get_swap_bio(GFP_KERNEL, page, end_swap_bio_read); 390 if (bio == NULL) { 391 unlock_page(page); 392 ret = -ENOMEM; 393 goto out; 394 } 395 disk = bio->bi_disk; 396 /* 397 * Keep this task valid during swap readpage because the oom killer may 398 * attempt to access it in the page fault retry time check. 399 */ 400 get_task_struct(current); 401 bio->bi_private = current; 402 bio_set_op_attrs(bio, REQ_OP_READ, 0); 403 count_vm_event(PSWPIN); 404 bio_get(bio); 405 qc = submit_bio(bio); 406 while (synchronous) { 407 set_current_state(TASK_UNINTERRUPTIBLE); 408 if (!READ_ONCE(bio->bi_private)) 409 break; 410 411 if (!blk_poll(disk->queue, qc)) 412 break; 413 } 414 __set_current_state(TASK_RUNNING); 415 bio_put(bio); 416 417 out: 418 return ret; 419 } 420 421 int swap_set_page_dirty(struct page *page) 422 { 423 struct swap_info_struct *sis = page_swap_info(page); 424 425 if (sis->flags & SWP_FILE) { 426 struct address_space *mapping = sis->swap_file->f_mapping; 427 428 VM_BUG_ON_PAGE(!PageSwapCache(page), page); 429 return mapping->a_ops->set_page_dirty(page); 430 } else { 431 return __set_page_dirty_no_writeback(page); 432 } 433 } 434