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 #include <asm/pgtable.h> 29 30 static struct bio *get_swap_bio(gfp_t gfp_flags, 31 struct page *page, bio_end_io_t end_io) 32 { 33 struct bio *bio; 34 35 bio = bio_alloc(gfp_flags, 1); 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 bio_add_page(bio, page, PAGE_SIZE * hpage_nr_pages(page), 0); 45 } 46 return bio; 47 } 48 49 void end_swap_bio_write(struct bio *bio) 50 { 51 struct page *page = bio_first_page_all(bio); 52 53 if (bio->bi_status) { 54 SetPageError(page); 55 /* 56 * We failed to write the page out to swap-space. 57 * Re-dirty the page in order to avoid it being reclaimed. 58 * Also print a dire warning that things will go BAD (tm) 59 * very quickly. 60 * 61 * Also clear PG_reclaim to avoid rotate_reclaimable_page() 62 */ 63 set_page_dirty(page); 64 pr_alert("Write-error on swap-device (%u:%u:%llu)\n", 65 MAJOR(bio_dev(bio)), MINOR(bio_dev(bio)), 66 (unsigned long long)bio->bi_iter.bi_sector); 67 ClearPageReclaim(page); 68 } 69 end_page_writeback(page); 70 bio_put(bio); 71 } 72 73 static void swap_slot_free_notify(struct page *page) 74 { 75 struct swap_info_struct *sis; 76 struct gendisk *disk; 77 swp_entry_t entry; 78 79 /* 80 * There is no guarantee that the page is in swap cache - the software 81 * suspend code (at least) uses end_swap_bio_read() against a non- 82 * swapcache page. So we must check PG_swapcache before proceeding with 83 * this optimization. 84 */ 85 if (unlikely(!PageSwapCache(page))) 86 return; 87 88 sis = page_swap_info(page); 89 if (!(sis->flags & SWP_BLKDEV)) 90 return; 91 92 /* 93 * The swap subsystem performs lazy swap slot freeing, 94 * expecting that the page will be swapped out again. 95 * So we can avoid an unnecessary write if the page 96 * isn't redirtied. 97 * This is good for real swap storage because we can 98 * reduce unnecessary I/O and enhance wear-leveling 99 * if an SSD is used as the as swap device. 100 * But if in-memory swap device (eg zram) is used, 101 * this causes a duplicated copy between uncompressed 102 * data in VM-owned memory and compressed data in 103 * zram-owned memory. So let's free zram-owned memory 104 * and make the VM-owned decompressed page *dirty*, 105 * so the page should be swapped out somewhere again if 106 * we again wish to reclaim it. 107 */ 108 disk = sis->bdev->bd_disk; 109 entry.val = page_private(page); 110 if (disk->fops->swap_slot_free_notify && __swap_count(entry) == 1) { 111 unsigned long offset; 112 113 offset = swp_offset(entry); 114 115 SetPageDirty(page); 116 disk->fops->swap_slot_free_notify(sis->bdev, 117 offset); 118 } 119 } 120 121 static void end_swap_bio_read(struct bio *bio) 122 { 123 struct page *page = bio_first_page_all(bio); 124 struct task_struct *waiter = bio->bi_private; 125 126 if (bio->bi_status) { 127 SetPageError(page); 128 ClearPageUptodate(page); 129 pr_alert("Read-error on swap-device (%u:%u:%llu)\n", 130 MAJOR(bio_dev(bio)), MINOR(bio_dev(bio)), 131 (unsigned long long)bio->bi_iter.bi_sector); 132 goto out; 133 } 134 135 SetPageUptodate(page); 136 swap_slot_free_notify(page); 137 out: 138 unlock_page(page); 139 WRITE_ONCE(bio->bi_private, NULL); 140 bio_put(bio); 141 if (waiter) { 142 blk_wake_io_task(waiter); 143 put_task_struct(waiter); 144 } 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 tree. 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 = probe_block; 181 ret = bmap(inode, &first_block); 182 if (ret || !first_block) 183 goto bad_bmap; 184 185 /* 186 * It must be PAGE_SIZE aligned on-disk 187 */ 188 if (first_block & (blocks_per_page - 1)) { 189 probe_block++; 190 goto reprobe; 191 } 192 193 for (block_in_page = 1; block_in_page < blocks_per_page; 194 block_in_page++) { 195 sector_t block; 196 197 block = probe_block + block_in_page; 198 ret = bmap(inode, &block); 199 if (ret || !block) 200 goto bad_bmap; 201 202 if (block != first_block + block_in_page) { 203 /* Discontiguity */ 204 probe_block++; 205 goto reprobe; 206 } 207 } 208 209 first_block >>= (PAGE_SHIFT - blkbits); 210 if (page_no) { /* exclude the header page */ 211 if (first_block < lowest_block) 212 lowest_block = first_block; 213 if (first_block > highest_block) 214 highest_block = first_block; 215 } 216 217 /* 218 * We found a PAGE_SIZE-length, PAGE_SIZE-aligned run of blocks 219 */ 220 ret = add_swap_extent(sis, page_no, 1, first_block); 221 if (ret < 0) 222 goto out; 223 nr_extents += ret; 224 page_no++; 225 probe_block += blocks_per_page; 226 reprobe: 227 continue; 228 } 229 ret = nr_extents; 230 *span = 1 + highest_block - lowest_block; 231 if (page_no == 0) 232 page_no = 1; /* force Empty message */ 233 sis->max = page_no; 234 sis->pages = page_no - 1; 235 sis->highest_bit = page_no - 1; 236 out: 237 return ret; 238 bad_bmap: 239 pr_err("swapon: swapfile has holes\n"); 240 ret = -EINVAL; 241 goto out; 242 } 243 244 /* 245 * We may have stale swap cache pages in memory: notice 246 * them here and get rid of the unnecessary final write. 247 */ 248 int swap_writepage(struct page *page, struct writeback_control *wbc) 249 { 250 int ret = 0; 251 252 if (try_to_free_swap(page)) { 253 unlock_page(page); 254 goto out; 255 } 256 if (frontswap_store(page) == 0) { 257 set_page_writeback(page); 258 unlock_page(page); 259 end_page_writeback(page); 260 goto out; 261 } 262 ret = __swap_writepage(page, wbc, end_swap_bio_write); 263 out: 264 return ret; 265 } 266 267 static sector_t swap_page_sector(struct page *page) 268 { 269 return (sector_t)__page_file_index(page) << (PAGE_SHIFT - 9); 270 } 271 272 static inline void count_swpout_vm_event(struct page *page) 273 { 274 #ifdef CONFIG_TRANSPARENT_HUGEPAGE 275 if (unlikely(PageTransHuge(page))) 276 count_vm_event(THP_SWPOUT); 277 #endif 278 count_vm_events(PSWPOUT, hpage_nr_pages(page)); 279 } 280 281 int __swap_writepage(struct page *page, struct writeback_control *wbc, 282 bio_end_io_t end_write_func) 283 { 284 struct bio *bio; 285 int ret; 286 struct swap_info_struct *sis = page_swap_info(page); 287 288 VM_BUG_ON_PAGE(!PageSwapCache(page), page); 289 if (sis->flags & SWP_FS) { 290 struct kiocb kiocb; 291 struct file *swap_file = sis->swap_file; 292 struct address_space *mapping = swap_file->f_mapping; 293 struct bio_vec bv = { 294 .bv_page = page, 295 .bv_len = PAGE_SIZE, 296 .bv_offset = 0 297 }; 298 struct iov_iter from; 299 300 iov_iter_bvec(&from, WRITE, &bv, 1, PAGE_SIZE); 301 init_sync_kiocb(&kiocb, swap_file); 302 kiocb.ki_pos = page_file_offset(page); 303 304 set_page_writeback(page); 305 unlock_page(page); 306 ret = mapping->a_ops->direct_IO(&kiocb, &from); 307 if (ret == PAGE_SIZE) { 308 count_vm_event(PSWPOUT); 309 ret = 0; 310 } else { 311 /* 312 * In the case of swap-over-nfs, this can be a 313 * temporary failure if the system has limited 314 * memory for allocating transmit buffers. 315 * Mark the page dirty and avoid 316 * rotate_reclaimable_page but rate-limit the 317 * messages but do not flag PageError like 318 * the normal direct-to-bio case as it could 319 * be temporary. 320 */ 321 set_page_dirty(page); 322 ClearPageReclaim(page); 323 pr_err_ratelimited("Write error on dio swapfile (%llu)\n", 324 page_file_offset(page)); 325 } 326 end_page_writeback(page); 327 return ret; 328 } 329 330 ret = bdev_write_page(sis->bdev, swap_page_sector(page), page, wbc); 331 if (!ret) { 332 count_swpout_vm_event(page); 333 return 0; 334 } 335 336 ret = 0; 337 bio = get_swap_bio(GFP_NOIO, page, end_write_func); 338 if (bio == NULL) { 339 set_page_dirty(page); 340 unlock_page(page); 341 ret = -ENOMEM; 342 goto out; 343 } 344 bio->bi_opf = REQ_OP_WRITE | REQ_SWAP | wbc_to_write_flags(wbc); 345 bio_associate_blkg_from_page(bio, page); 346 count_swpout_vm_event(page); 347 set_page_writeback(page); 348 unlock_page(page); 349 submit_bio(bio); 350 out: 351 return ret; 352 } 353 354 int swap_readpage(struct page *page, bool synchronous) 355 { 356 struct bio *bio; 357 int ret = 0; 358 struct swap_info_struct *sis = page_swap_info(page); 359 blk_qc_t qc; 360 struct gendisk *disk; 361 unsigned long pflags; 362 363 VM_BUG_ON_PAGE(!PageSwapCache(page) && !synchronous, page); 364 VM_BUG_ON_PAGE(!PageLocked(page), page); 365 VM_BUG_ON_PAGE(PageUptodate(page), page); 366 367 /* 368 * Count submission time as memory stall. When the device is congested, 369 * or the submitting cgroup IO-throttled, submission can be a 370 * significant part of overall IO time. 371 */ 372 psi_memstall_enter(&pflags); 373 374 if (frontswap_load(page) == 0) { 375 SetPageUptodate(page); 376 unlock_page(page); 377 goto out; 378 } 379 380 if (sis->flags & SWP_FS) { 381 struct file *swap_file = sis->swap_file; 382 struct address_space *mapping = swap_file->f_mapping; 383 384 ret = mapping->a_ops->readpage(swap_file, page); 385 if (!ret) 386 count_vm_event(PSWPIN); 387 goto out; 388 } 389 390 ret = bdev_read_page(sis->bdev, swap_page_sector(page), page); 391 if (!ret) { 392 if (trylock_page(page)) { 393 swap_slot_free_notify(page); 394 unlock_page(page); 395 } 396 397 count_vm_event(PSWPIN); 398 goto out; 399 } 400 401 ret = 0; 402 bio = get_swap_bio(GFP_KERNEL, page, end_swap_bio_read); 403 if (bio == NULL) { 404 unlock_page(page); 405 ret = -ENOMEM; 406 goto out; 407 } 408 disk = bio->bi_disk; 409 /* 410 * Keep this task valid during swap readpage because the oom killer may 411 * attempt to access it in the page fault retry time check. 412 */ 413 bio_set_op_attrs(bio, REQ_OP_READ, 0); 414 if (synchronous) { 415 bio->bi_opf |= REQ_HIPRI; 416 get_task_struct(current); 417 bio->bi_private = current; 418 } 419 count_vm_event(PSWPIN); 420 bio_get(bio); 421 qc = submit_bio(bio); 422 while (synchronous) { 423 set_current_state(TASK_UNINTERRUPTIBLE); 424 if (!READ_ONCE(bio->bi_private)) 425 break; 426 427 if (!blk_poll(disk->queue, qc, true)) 428 io_schedule(); 429 } 430 __set_current_state(TASK_RUNNING); 431 bio_put(bio); 432 433 out: 434 psi_memstall_leave(&pflags); 435 return ret; 436 } 437 438 int swap_set_page_dirty(struct page *page) 439 { 440 struct swap_info_struct *sis = page_swap_info(page); 441 442 if (sis->flags & SWP_FS) { 443 struct address_space *mapping = sis->swap_file->f_mapping; 444 445 VM_BUG_ON_PAGE(!PageSwapCache(page), page); 446 return mapping->a_ops->set_page_dirty(page); 447 } else { 448 return __set_page_dirty_no_writeback(page); 449 } 450 } 451