1 /* 2 * linux/mm/page_io.c 3 * 4 * Copyright (C) 1991, 1992, 1993, 1994 Linus Torvalds 5 * 6 * Swap reorganised 29.12.95, 7 * Asynchronous swapping added 30.12.95. Stephen Tweedie 8 * Removed race in async swapping. 14.4.1996. Bruno Haible 9 * Add swap of shared pages through the page cache. 20.2.1998. Stephen Tweedie 10 * Always use brw_page, life becomes simpler. 12 May 1998 Eric Biederman 11 */ 12 13 #include <linux/mm.h> 14 #include <linux/kernel_stat.h> 15 #include <linux/gfp.h> 16 #include <linux/pagemap.h> 17 #include <linux/swap.h> 18 #include <linux/bio.h> 19 #include <linux/swapops.h> 20 #include <linux/buffer_head.h> 21 #include <linux/writeback.h> 22 #include <linux/frontswap.h> 23 #include <linux/blkdev.h> 24 #include <linux/uio.h> 25 #include <linux/sched/task.h> 26 #include <asm/pgtable.h> 27 28 static struct bio *get_swap_bio(gfp_t gfp_flags, 29 struct page *page, bio_end_io_t end_io) 30 { 31 int i, nr = hpage_nr_pages(page); 32 struct bio *bio; 33 34 bio = bio_alloc(gfp_flags, nr); 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 for (i = 0; i < nr; i++) 44 bio_add_page(bio, page + i, PAGE_SIZE, 0); 45 VM_BUG_ON(bio->bi_iter.bi_size != PAGE_SIZE * nr); 46 } 47 return bio; 48 } 49 50 void end_swap_bio_write(struct bio *bio) 51 { 52 struct page *page = bio->bi_io_vec[0].bv_page; 53 54 if (bio->bi_status) { 55 SetPageError(page); 56 /* 57 * We failed to write the page out to swap-space. 58 * Re-dirty the page in order to avoid it being reclaimed. 59 * Also print a dire warning that things will go BAD (tm) 60 * very quickly. 61 * 62 * Also clear PG_reclaim to avoid rotate_reclaimable_page() 63 */ 64 set_page_dirty(page); 65 pr_alert("Write-error on swap-device (%u:%u:%llu)\n", 66 MAJOR(bio_dev(bio)), MINOR(bio_dev(bio)), 67 (unsigned long long)bio->bi_iter.bi_sector); 68 ClearPageReclaim(page); 69 } 70 end_page_writeback(page); 71 bio_put(bio); 72 } 73 74 static void swap_slot_free_notify(struct page *page) 75 { 76 struct swap_info_struct *sis; 77 struct gendisk *disk; 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 if (disk->fops->swap_slot_free_notify) { 110 swp_entry_t entry; 111 unsigned long offset; 112 113 entry.val = page_private(page); 114 offset = swp_offset(entry); 115 116 SetPageDirty(page); 117 disk->fops->swap_slot_free_notify(sis->bdev, 118 offset); 119 } 120 } 121 122 static void end_swap_bio_read(struct bio *bio) 123 { 124 struct page *page = bio->bi_io_vec[0].bv_page; 125 struct task_struct *waiter = bio->bi_private; 126 127 if (bio->bi_status) { 128 SetPageError(page); 129 ClearPageUptodate(page); 130 pr_alert("Read-error on swap-device (%u:%u:%llu)\n", 131 MAJOR(bio_dev(bio)), MINOR(bio_dev(bio)), 132 (unsigned long long)bio->bi_iter.bi_sector); 133 goto out; 134 } 135 136 SetPageUptodate(page); 137 swap_slot_free_notify(page); 138 out: 139 unlock_page(page); 140 WRITE_ONCE(bio->bi_private, NULL); 141 bio_put(bio); 142 wake_up_process(waiter); 143 put_task_struct(waiter); 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 list. 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 = bmap(inode, probe_block); 180 if (first_block == 0) 181 goto bad_bmap; 182 183 /* 184 * It must be PAGE_SIZE aligned on-disk 185 */ 186 if (first_block & (blocks_per_page - 1)) { 187 probe_block++; 188 goto reprobe; 189 } 190 191 for (block_in_page = 1; block_in_page < blocks_per_page; 192 block_in_page++) { 193 sector_t block; 194 195 block = bmap(inode, probe_block + block_in_page); 196 if (block == 0) 197 goto bad_bmap; 198 if (block != first_block + block_in_page) { 199 /* Discontiguity */ 200 probe_block++; 201 goto reprobe; 202 } 203 } 204 205 first_block >>= (PAGE_SHIFT - blkbits); 206 if (page_no) { /* exclude the header page */ 207 if (first_block < lowest_block) 208 lowest_block = first_block; 209 if (first_block > highest_block) 210 highest_block = first_block; 211 } 212 213 /* 214 * We found a PAGE_SIZE-length, PAGE_SIZE-aligned run of blocks 215 */ 216 ret = add_swap_extent(sis, page_no, 1, first_block); 217 if (ret < 0) 218 goto out; 219 nr_extents += ret; 220 page_no++; 221 probe_block += blocks_per_page; 222 reprobe: 223 continue; 224 } 225 ret = nr_extents; 226 *span = 1 + highest_block - lowest_block; 227 if (page_no == 0) 228 page_no = 1; /* force Empty message */ 229 sis->max = page_no; 230 sis->pages = page_no - 1; 231 sis->highest_bit = page_no - 1; 232 out: 233 return ret; 234 bad_bmap: 235 pr_err("swapon: swapfile has holes\n"); 236 ret = -EINVAL; 237 goto out; 238 } 239 240 /* 241 * We may have stale swap cache pages in memory: notice 242 * them here and get rid of the unnecessary final write. 243 */ 244 int swap_writepage(struct page *page, struct writeback_control *wbc) 245 { 246 int ret = 0; 247 248 if (try_to_free_swap(page)) { 249 unlock_page(page); 250 goto out; 251 } 252 if (frontswap_store(page) == 0) { 253 set_page_writeback(page); 254 unlock_page(page); 255 end_page_writeback(page); 256 goto out; 257 } 258 ret = __swap_writepage(page, wbc, end_swap_bio_write); 259 out: 260 return ret; 261 } 262 263 static sector_t swap_page_sector(struct page *page) 264 { 265 return (sector_t)__page_file_index(page) << (PAGE_SHIFT - 9); 266 } 267 268 static inline void count_swpout_vm_event(struct page *page) 269 { 270 #ifdef CONFIG_TRANSPARENT_HUGEPAGE 271 if (unlikely(PageTransHuge(page))) 272 count_vm_event(THP_SWPOUT); 273 #endif 274 count_vm_events(PSWPOUT, hpage_nr_pages(page)); 275 } 276 277 int __swap_writepage(struct page *page, struct writeback_control *wbc, 278 bio_end_io_t end_write_func) 279 { 280 struct bio *bio; 281 int ret; 282 struct swap_info_struct *sis = page_swap_info(page); 283 284 VM_BUG_ON_PAGE(!PageSwapCache(page), page); 285 if (sis->flags & SWP_FILE) { 286 struct kiocb kiocb; 287 struct file *swap_file = sis->swap_file; 288 struct address_space *mapping = swap_file->f_mapping; 289 struct bio_vec bv = { 290 .bv_page = page, 291 .bv_len = PAGE_SIZE, 292 .bv_offset = 0 293 }; 294 struct iov_iter from; 295 296 iov_iter_bvec(&from, ITER_BVEC | WRITE, &bv, 1, PAGE_SIZE); 297 init_sync_kiocb(&kiocb, swap_file); 298 kiocb.ki_pos = page_file_offset(page); 299 300 set_page_writeback(page); 301 unlock_page(page); 302 ret = mapping->a_ops->direct_IO(&kiocb, &from); 303 if (ret == PAGE_SIZE) { 304 count_vm_event(PSWPOUT); 305 ret = 0; 306 } else { 307 /* 308 * In the case of swap-over-nfs, this can be a 309 * temporary failure if the system has limited 310 * memory for allocating transmit buffers. 311 * Mark the page dirty and avoid 312 * rotate_reclaimable_page but rate-limit the 313 * messages but do not flag PageError like 314 * the normal direct-to-bio case as it could 315 * be temporary. 316 */ 317 set_page_dirty(page); 318 ClearPageReclaim(page); 319 pr_err_ratelimited("Write error on dio swapfile (%llu)\n", 320 page_file_offset(page)); 321 } 322 end_page_writeback(page); 323 return ret; 324 } 325 326 ret = bdev_write_page(sis->bdev, swap_page_sector(page), page, wbc); 327 if (!ret) { 328 count_swpout_vm_event(page); 329 return 0; 330 } 331 332 ret = 0; 333 bio = get_swap_bio(GFP_NOIO, page, end_write_func); 334 if (bio == NULL) { 335 set_page_dirty(page); 336 unlock_page(page); 337 ret = -ENOMEM; 338 goto out; 339 } 340 bio->bi_opf = REQ_OP_WRITE | wbc_to_write_flags(wbc); 341 count_swpout_vm_event(page); 342 set_page_writeback(page); 343 unlock_page(page); 344 submit_bio(bio); 345 out: 346 return ret; 347 } 348 349 int swap_readpage(struct page *page, bool do_poll) 350 { 351 struct bio *bio; 352 int ret = 0; 353 struct swap_info_struct *sis = page_swap_info(page); 354 blk_qc_t qc; 355 struct gendisk *disk; 356 357 VM_BUG_ON_PAGE(!PageSwapCache(page), page); 358 VM_BUG_ON_PAGE(!PageLocked(page), page); 359 VM_BUG_ON_PAGE(PageUptodate(page), page); 360 if (frontswap_load(page) == 0) { 361 SetPageUptodate(page); 362 unlock_page(page); 363 goto out; 364 } 365 366 if (sis->flags & SWP_FILE) { 367 struct file *swap_file = sis->swap_file; 368 struct address_space *mapping = swap_file->f_mapping; 369 370 ret = mapping->a_ops->readpage(swap_file, page); 371 if (!ret) 372 count_vm_event(PSWPIN); 373 return ret; 374 } 375 376 ret = bdev_read_page(sis->bdev, swap_page_sector(page), page); 377 if (!ret) { 378 if (trylock_page(page)) { 379 swap_slot_free_notify(page); 380 unlock_page(page); 381 } 382 383 count_vm_event(PSWPIN); 384 return 0; 385 } 386 387 ret = 0; 388 bio = get_swap_bio(GFP_KERNEL, page, end_swap_bio_read); 389 if (bio == NULL) { 390 unlock_page(page); 391 ret = -ENOMEM; 392 goto out; 393 } 394 disk = bio->bi_disk; 395 /* 396 * Keep this task valid during swap readpage because the oom killer may 397 * attempt to access it in the page fault retry time check. 398 */ 399 get_task_struct(current); 400 bio->bi_private = current; 401 bio_set_op_attrs(bio, REQ_OP_READ, 0); 402 count_vm_event(PSWPIN); 403 bio_get(bio); 404 qc = submit_bio(bio); 405 while (do_poll) { 406 set_current_state(TASK_UNINTERRUPTIBLE); 407 if (!READ_ONCE(bio->bi_private)) 408 break; 409 410 if (!blk_mq_poll(disk->queue, qc)) 411 break; 412 } 413 __set_current_state(TASK_RUNNING); 414 bio_put(bio); 415 416 out: 417 return ret; 418 } 419 420 int swap_set_page_dirty(struct page *page) 421 { 422 struct swap_info_struct *sis = page_swap_info(page); 423 424 if (sis->flags & SWP_FILE) { 425 struct address_space *mapping = sis->swap_file->f_mapping; 426 427 VM_BUG_ON_PAGE(!PageSwapCache(page), page); 428 return mapping->a_ops->set_page_dirty(page); 429 } else { 430 return __set_page_dirty_no_writeback(page); 431 } 432 } 433