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 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 77 /* 78 * There is no guarantee that the page is in swap cache - the software 79 * suspend code (at least) uses end_swap_bio_read() against a non- 80 * swapcache page. So we must check PG_swapcache before proceeding with 81 * this optimization. 82 */ 83 if (unlikely(!PageSwapCache(page))) 84 return; 85 86 sis = page_swap_info(page); 87 if (!(sis->flags & SWP_BLKDEV)) 88 return; 89 90 /* 91 * The swap subsystem performs lazy swap slot freeing, 92 * expecting that the page will be swapped out again. 93 * So we can avoid an unnecessary write if the page 94 * isn't redirtied. 95 * This is good for real swap storage because we can 96 * reduce unnecessary I/O and enhance wear-leveling 97 * if an SSD is used as the as swap device. 98 * But if in-memory swap device (eg zram) is used, 99 * this causes a duplicated copy between uncompressed 100 * data in VM-owned memory and compressed data in 101 * zram-owned memory. So let's free zram-owned memory 102 * and make the VM-owned decompressed page *dirty*, 103 * so the page should be swapped out somewhere again if 104 * we again wish to reclaim it. 105 */ 106 disk = sis->bdev->bd_disk; 107 if (disk->fops->swap_slot_free_notify) { 108 swp_entry_t entry; 109 unsigned long offset; 110 111 entry.val = page_private(page); 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 blk_wake_io_task(waiter); 141 put_task_struct(waiter); 142 } 143 144 int generic_swapfile_activate(struct swap_info_struct *sis, 145 struct file *swap_file, 146 sector_t *span) 147 { 148 struct address_space *mapping = swap_file->f_mapping; 149 struct inode *inode = mapping->host; 150 unsigned blocks_per_page; 151 unsigned long page_no; 152 unsigned blkbits; 153 sector_t probe_block; 154 sector_t last_block; 155 sector_t lowest_block = -1; 156 sector_t highest_block = 0; 157 int nr_extents = 0; 158 int ret; 159 160 blkbits = inode->i_blkbits; 161 blocks_per_page = PAGE_SIZE >> blkbits; 162 163 /* 164 * Map all the blocks into the extent list. This code doesn't try 165 * to be very smart. 166 */ 167 probe_block = 0; 168 page_no = 0; 169 last_block = i_size_read(inode) >> blkbits; 170 while ((probe_block + blocks_per_page) <= last_block && 171 page_no < sis->max) { 172 unsigned block_in_page; 173 sector_t first_block; 174 175 cond_resched(); 176 177 first_block = bmap(inode, probe_block); 178 if (first_block == 0) 179 goto bad_bmap; 180 181 /* 182 * It must be PAGE_SIZE aligned on-disk 183 */ 184 if (first_block & (blocks_per_page - 1)) { 185 probe_block++; 186 goto reprobe; 187 } 188 189 for (block_in_page = 1; block_in_page < blocks_per_page; 190 block_in_page++) { 191 sector_t block; 192 193 block = bmap(inode, probe_block + block_in_page); 194 if (block == 0) 195 goto bad_bmap; 196 if (block != first_block + block_in_page) { 197 /* Discontiguity */ 198 probe_block++; 199 goto reprobe; 200 } 201 } 202 203 first_block >>= (PAGE_SHIFT - blkbits); 204 if (page_no) { /* exclude the header page */ 205 if (first_block < lowest_block) 206 lowest_block = first_block; 207 if (first_block > highest_block) 208 highest_block = first_block; 209 } 210 211 /* 212 * We found a PAGE_SIZE-length, PAGE_SIZE-aligned run of blocks 213 */ 214 ret = add_swap_extent(sis, page_no, 1, first_block); 215 if (ret < 0) 216 goto out; 217 nr_extents += ret; 218 page_no++; 219 probe_block += blocks_per_page; 220 reprobe: 221 continue; 222 } 223 ret = nr_extents; 224 *span = 1 + highest_block - lowest_block; 225 if (page_no == 0) 226 page_no = 1; /* force Empty message */ 227 sis->max = page_no; 228 sis->pages = page_no - 1; 229 sis->highest_bit = page_no - 1; 230 out: 231 return ret; 232 bad_bmap: 233 pr_err("swapon: swapfile has holes\n"); 234 ret = -EINVAL; 235 goto out; 236 } 237 238 /* 239 * We may have stale swap cache pages in memory: notice 240 * them here and get rid of the unnecessary final write. 241 */ 242 int swap_writepage(struct page *page, struct writeback_control *wbc) 243 { 244 int ret = 0; 245 246 if (try_to_free_swap(page)) { 247 unlock_page(page); 248 goto out; 249 } 250 if (frontswap_store(page) == 0) { 251 set_page_writeback(page); 252 unlock_page(page); 253 end_page_writeback(page); 254 goto out; 255 } 256 ret = __swap_writepage(page, wbc, end_swap_bio_write); 257 out: 258 return ret; 259 } 260 261 static sector_t swap_page_sector(struct page *page) 262 { 263 return (sector_t)__page_file_index(page) << (PAGE_SHIFT - 9); 264 } 265 266 static inline void count_swpout_vm_event(struct page *page) 267 { 268 #ifdef CONFIG_TRANSPARENT_HUGEPAGE 269 if (unlikely(PageTransHuge(page))) 270 count_vm_event(THP_SWPOUT); 271 #endif 272 count_vm_events(PSWPOUT, hpage_nr_pages(page)); 273 } 274 275 int __swap_writepage(struct page *page, struct writeback_control *wbc, 276 bio_end_io_t end_write_func) 277 { 278 struct bio *bio; 279 int ret; 280 struct swap_info_struct *sis = page_swap_info(page); 281 282 VM_BUG_ON_PAGE(!PageSwapCache(page), page); 283 if (sis->flags & SWP_FS) { 284 struct kiocb kiocb; 285 struct file *swap_file = sis->swap_file; 286 struct address_space *mapping = swap_file->f_mapping; 287 struct bio_vec bv = { 288 .bv_page = page, 289 .bv_len = PAGE_SIZE, 290 .bv_offset = 0 291 }; 292 struct iov_iter from; 293 294 iov_iter_bvec(&from, WRITE, &bv, 1, PAGE_SIZE); 295 init_sync_kiocb(&kiocb, swap_file); 296 kiocb.ki_pos = page_file_offset(page); 297 298 set_page_writeback(page); 299 unlock_page(page); 300 ret = mapping->a_ops->direct_IO(&kiocb, &from); 301 if (ret == PAGE_SIZE) { 302 count_vm_event(PSWPOUT); 303 ret = 0; 304 } else { 305 /* 306 * In the case of swap-over-nfs, this can be a 307 * temporary failure if the system has limited 308 * memory for allocating transmit buffers. 309 * Mark the page dirty and avoid 310 * rotate_reclaimable_page but rate-limit the 311 * messages but do not flag PageError like 312 * the normal direct-to-bio case as it could 313 * be temporary. 314 */ 315 set_page_dirty(page); 316 ClearPageReclaim(page); 317 pr_err_ratelimited("Write error on dio swapfile (%llu)\n", 318 page_file_offset(page)); 319 } 320 end_page_writeback(page); 321 return ret; 322 } 323 324 ret = bdev_write_page(sis->bdev, swap_page_sector(page), page, wbc); 325 if (!ret) { 326 count_swpout_vm_event(page); 327 return 0; 328 } 329 330 ret = 0; 331 bio = get_swap_bio(GFP_NOIO, page, end_write_func); 332 if (bio == NULL) { 333 set_page_dirty(page); 334 unlock_page(page); 335 ret = -ENOMEM; 336 goto out; 337 } 338 bio->bi_opf = REQ_OP_WRITE | REQ_SWAP | wbc_to_write_flags(wbc); 339 bio_associate_blkg_from_page(bio, page); 340 count_swpout_vm_event(page); 341 set_page_writeback(page); 342 unlock_page(page); 343 submit_bio(bio); 344 out: 345 return ret; 346 } 347 348 int swap_readpage(struct page *page, bool synchronous) 349 { 350 struct bio *bio; 351 int ret = 0; 352 struct swap_info_struct *sis = page_swap_info(page); 353 blk_qc_t qc; 354 struct gendisk *disk; 355 356 VM_BUG_ON_PAGE(!PageSwapCache(page) && !synchronous, page); 357 VM_BUG_ON_PAGE(!PageLocked(page), page); 358 VM_BUG_ON_PAGE(PageUptodate(page), page); 359 if (frontswap_load(page) == 0) { 360 SetPageUptodate(page); 361 unlock_page(page); 362 goto out; 363 } 364 365 if (sis->flags & SWP_FS) { 366 struct file *swap_file = sis->swap_file; 367 struct address_space *mapping = swap_file->f_mapping; 368 369 ret = mapping->a_ops->readpage(swap_file, page); 370 if (!ret) 371 count_vm_event(PSWPIN); 372 return ret; 373 } 374 375 ret = bdev_read_page(sis->bdev, swap_page_sector(page), page); 376 if (!ret) { 377 if (trylock_page(page)) { 378 swap_slot_free_notify(page); 379 unlock_page(page); 380 } 381 382 count_vm_event(PSWPIN); 383 return 0; 384 } 385 386 ret = 0; 387 bio = get_swap_bio(GFP_KERNEL, page, end_swap_bio_read); 388 if (bio == NULL) { 389 unlock_page(page); 390 ret = -ENOMEM; 391 goto out; 392 } 393 disk = bio->bi_disk; 394 /* 395 * Keep this task valid during swap readpage because the oom killer may 396 * attempt to access it in the page fault retry time check. 397 */ 398 get_task_struct(current); 399 bio->bi_private = current; 400 bio_set_op_attrs(bio, REQ_OP_READ, 0); 401 if (synchronous) 402 bio->bi_opf |= REQ_HIPRI; 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, true)) 412 io_schedule(); 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_FS) { 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