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 = 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_FS) { 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, 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 | REQ_SWAP | wbc_to_write_flags(wbc); 342 bio_associate_blkg_from_page(bio, page); 343 count_swpout_vm_event(page); 344 set_page_writeback(page); 345 unlock_page(page); 346 submit_bio(bio); 347 out: 348 return ret; 349 } 350 351 int swap_readpage(struct page *page, bool synchronous) 352 { 353 struct bio *bio; 354 int ret = 0; 355 struct swap_info_struct *sis = page_swap_info(page); 356 blk_qc_t qc; 357 struct gendisk *disk; 358 unsigned long pflags; 359 360 VM_BUG_ON_PAGE(!PageSwapCache(page) && !synchronous, page); 361 VM_BUG_ON_PAGE(!PageLocked(page), page); 362 VM_BUG_ON_PAGE(PageUptodate(page), page); 363 364 /* 365 * Count submission time as memory stall. When the device is congested, 366 * or the submitting cgroup IO-throttled, submission can be a 367 * significant part of overall IO time. 368 */ 369 psi_memstall_enter(&pflags); 370 371 if (frontswap_load(page) == 0) { 372 SetPageUptodate(page); 373 unlock_page(page); 374 goto out; 375 } 376 377 if (sis->flags & SWP_FS) { 378 struct file *swap_file = sis->swap_file; 379 struct address_space *mapping = swap_file->f_mapping; 380 381 ret = mapping->a_ops->readpage(swap_file, page); 382 if (!ret) 383 count_vm_event(PSWPIN); 384 goto out; 385 } 386 387 ret = bdev_read_page(sis->bdev, swap_page_sector(page), page); 388 if (!ret) { 389 if (trylock_page(page)) { 390 swap_slot_free_notify(page); 391 unlock_page(page); 392 } 393 394 count_vm_event(PSWPIN); 395 goto out; 396 } 397 398 ret = 0; 399 bio = get_swap_bio(GFP_KERNEL, page, end_swap_bio_read); 400 if (bio == NULL) { 401 unlock_page(page); 402 ret = -ENOMEM; 403 goto out; 404 } 405 disk = bio->bi_disk; 406 /* 407 * Keep this task valid during swap readpage because the oom killer may 408 * attempt to access it in the page fault retry time check. 409 */ 410 bio_set_op_attrs(bio, REQ_OP_READ, 0); 411 if (synchronous) { 412 bio->bi_opf |= REQ_HIPRI; 413 get_task_struct(current); 414 bio->bi_private = current; 415 } 416 count_vm_event(PSWPIN); 417 bio_get(bio); 418 qc = submit_bio(bio); 419 while (synchronous) { 420 set_current_state(TASK_UNINTERRUPTIBLE); 421 if (!READ_ONCE(bio->bi_private)) 422 break; 423 424 if (!blk_poll(disk->queue, qc, true)) 425 io_schedule(); 426 } 427 __set_current_state(TASK_RUNNING); 428 bio_put(bio); 429 430 out: 431 psi_memstall_leave(&pflags); 432 return ret; 433 } 434 435 int swap_set_page_dirty(struct page *page) 436 { 437 struct swap_info_struct *sis = page_swap_info(page); 438 439 if (sis->flags & SWP_FS) { 440 struct address_space *mapping = sis->swap_file->f_mapping; 441 442 VM_BUG_ON_PAGE(!PageSwapCache(page), page); 443 return mapping->a_ops->set_page_dirty(page); 444 } else { 445 return __set_page_dirty_no_writeback(page); 446 } 447 } 448