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
get_swap_bio(gfp_t gfp_flags,struct page * page,bio_end_io_t end_io)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
end_swap_bio_write(struct bio * bio)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
swap_slot_free_notify(struct page * page)75 static void swap_slot_free_notify(struct page *page)
76 {
77 struct swap_info_struct *sis;
78 struct gendisk *disk;
79 swp_entry_t entry;
80
81 /*
82 * There is no guarantee that the page is in swap cache - the software
83 * suspend code (at least) uses end_swap_bio_read() against a non-
84 * swapcache page. So we must check PG_swapcache before proceeding with
85 * this optimization.
86 */
87 if (unlikely(!PageSwapCache(page)))
88 return;
89
90 sis = page_swap_info(page);
91 if (!(sis->flags & SWP_BLKDEV))
92 return;
93
94 /*
95 * The swap subsystem performs lazy swap slot freeing,
96 * expecting that the page will be swapped out again.
97 * So we can avoid an unnecessary write if the page
98 * isn't redirtied.
99 * This is good for real swap storage because we can
100 * reduce unnecessary I/O and enhance wear-leveling
101 * if an SSD is used as the as swap device.
102 * But if in-memory swap device (eg zram) is used,
103 * this causes a duplicated copy between uncompressed
104 * data in VM-owned memory and compressed data in
105 * zram-owned memory. So let's free zram-owned memory
106 * and make the VM-owned decompressed page *dirty*,
107 * so the page should be swapped out somewhere again if
108 * we again wish to reclaim it.
109 */
110 disk = sis->bdev->bd_disk;
111 entry.val = page_private(page);
112 if (disk->fops->swap_slot_free_notify &&
113 __swap_count(sis, entry) == 1) {
114 unsigned long offset;
115
116 offset = swp_offset(entry);
117
118 SetPageDirty(page);
119 disk->fops->swap_slot_free_notify(sis->bdev,
120 offset);
121 }
122 }
123
end_swap_bio_read(struct bio * bio)124 static void end_swap_bio_read(struct bio *bio)
125 {
126 struct page *page = bio_first_page_all(bio);
127 struct task_struct *waiter = bio->bi_private;
128
129 if (bio->bi_status) {
130 SetPageError(page);
131 ClearPageUptodate(page);
132 pr_alert("Read-error on swap-device (%u:%u:%llu)\n",
133 MAJOR(bio_dev(bio)), MINOR(bio_dev(bio)),
134 (unsigned long long)bio->bi_iter.bi_sector);
135 goto out;
136 }
137
138 SetPageUptodate(page);
139 swap_slot_free_notify(page);
140 out:
141 unlock_page(page);
142 WRITE_ONCE(bio->bi_private, NULL);
143 bio_put(bio);
144 wake_up_process(waiter);
145 put_task_struct(waiter);
146 }
147
generic_swapfile_activate(struct swap_info_struct * sis,struct file * swap_file,sector_t * span)148 int generic_swapfile_activate(struct swap_info_struct *sis,
149 struct file *swap_file,
150 sector_t *span)
151 {
152 struct address_space *mapping = swap_file->f_mapping;
153 struct inode *inode = mapping->host;
154 unsigned blocks_per_page;
155 unsigned long page_no;
156 unsigned blkbits;
157 sector_t probe_block;
158 sector_t last_block;
159 sector_t lowest_block = -1;
160 sector_t highest_block = 0;
161 int nr_extents = 0;
162 int ret;
163
164 blkbits = inode->i_blkbits;
165 blocks_per_page = PAGE_SIZE >> blkbits;
166
167 /*
168 * Map all the blocks into the extent list. This code doesn't try
169 * to be very smart.
170 */
171 probe_block = 0;
172 page_no = 0;
173 last_block = i_size_read(inode) >> blkbits;
174 while ((probe_block + blocks_per_page) <= last_block &&
175 page_no < sis->max) {
176 unsigned block_in_page;
177 sector_t first_block;
178
179 cond_resched();
180
181 first_block = bmap(inode, probe_block);
182 if (first_block == 0)
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 = bmap(inode, probe_block + block_in_page);
198 if (block == 0)
199 goto bad_bmap;
200 if (block != first_block + block_in_page) {
201 /* Discontiguity */
202 probe_block++;
203 goto reprobe;
204 }
205 }
206
207 first_block >>= (PAGE_SHIFT - blkbits);
208 if (page_no) { /* exclude the header page */
209 if (first_block < lowest_block)
210 lowest_block = first_block;
211 if (first_block > highest_block)
212 highest_block = first_block;
213 }
214
215 /*
216 * We found a PAGE_SIZE-length, PAGE_SIZE-aligned run of blocks
217 */
218 ret = add_swap_extent(sis, page_no, 1, first_block);
219 if (ret < 0)
220 goto out;
221 nr_extents += ret;
222 page_no++;
223 probe_block += blocks_per_page;
224 reprobe:
225 continue;
226 }
227 ret = nr_extents;
228 *span = 1 + highest_block - lowest_block;
229 if (page_no == 0)
230 page_no = 1; /* force Empty message */
231 sis->max = page_no;
232 sis->pages = page_no - 1;
233 sis->highest_bit = page_no - 1;
234 out:
235 return ret;
236 bad_bmap:
237 pr_err("swapon: swapfile has holes\n");
238 ret = -EINVAL;
239 goto out;
240 }
241
242 /*
243 * We may have stale swap cache pages in memory: notice
244 * them here and get rid of the unnecessary final write.
245 */
swap_writepage(struct page * page,struct writeback_control * wbc)246 int swap_writepage(struct page *page, struct writeback_control *wbc)
247 {
248 int ret = 0;
249
250 if (try_to_free_swap(page)) {
251 unlock_page(page);
252 goto out;
253 }
254 if (frontswap_store(page) == 0) {
255 set_page_writeback(page);
256 unlock_page(page);
257 end_page_writeback(page);
258 goto out;
259 }
260 ret = __swap_writepage(page, wbc, end_swap_bio_write);
261 out:
262 return ret;
263 }
264
swap_page_sector(struct page * page)265 static sector_t swap_page_sector(struct page *page)
266 {
267 return (sector_t)__page_file_index(page) << (PAGE_SHIFT - 9);
268 }
269
count_swpout_vm_event(struct page * page)270 static inline void count_swpout_vm_event(struct page *page)
271 {
272 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
273 if (unlikely(PageTransHuge(page)))
274 count_vm_event(THP_SWPOUT);
275 #endif
276 count_vm_events(PSWPOUT, hpage_nr_pages(page));
277 }
278
__swap_writepage(struct page * page,struct writeback_control * wbc,bio_end_io_t end_write_func)279 int __swap_writepage(struct page *page, struct writeback_control *wbc,
280 bio_end_io_t end_write_func)
281 {
282 struct bio *bio;
283 int ret;
284 struct swap_info_struct *sis = page_swap_info(page);
285
286 VM_BUG_ON_PAGE(!PageSwapCache(page), page);
287 if (sis->flags & SWP_FILE) {
288 struct kiocb kiocb;
289 struct file *swap_file = sis->swap_file;
290 struct address_space *mapping = swap_file->f_mapping;
291 struct bio_vec bv = {
292 .bv_page = page,
293 .bv_len = PAGE_SIZE,
294 .bv_offset = 0
295 };
296 struct iov_iter from;
297
298 iov_iter_bvec(&from, ITER_BVEC | WRITE, &bv, 1, PAGE_SIZE);
299 init_sync_kiocb(&kiocb, swap_file);
300 kiocb.ki_pos = page_file_offset(page);
301
302 set_page_writeback(page);
303 unlock_page(page);
304 ret = mapping->a_ops->direct_IO(&kiocb, &from);
305 if (ret == PAGE_SIZE) {
306 count_vm_event(PSWPOUT);
307 ret = 0;
308 } else {
309 /*
310 * In the case of swap-over-nfs, this can be a
311 * temporary failure if the system has limited
312 * memory for allocating transmit buffers.
313 * Mark the page dirty and avoid
314 * rotate_reclaimable_page but rate-limit the
315 * messages but do not flag PageError like
316 * the normal direct-to-bio case as it could
317 * be temporary.
318 */
319 set_page_dirty(page);
320 ClearPageReclaim(page);
321 pr_err_ratelimited("Write error on dio swapfile (%llu)\n",
322 page_file_offset(page));
323 }
324 end_page_writeback(page);
325 return ret;
326 }
327
328 ret = bdev_write_page(sis->bdev, swap_page_sector(page), page, wbc);
329 if (!ret) {
330 count_swpout_vm_event(page);
331 return 0;
332 }
333
334 ret = 0;
335 bio = get_swap_bio(GFP_NOIO, page, end_write_func);
336 if (bio == NULL) {
337 set_page_dirty(page);
338 unlock_page(page);
339 ret = -ENOMEM;
340 goto out;
341 }
342 bio->bi_opf = REQ_OP_WRITE | REQ_SWAP | wbc_to_write_flags(wbc);
343 bio_associate_blkcg_from_page(bio, page);
344 count_swpout_vm_event(page);
345 set_page_writeback(page);
346 unlock_page(page);
347 submit_bio(bio);
348 out:
349 return ret;
350 }
351
swap_readpage(struct page * page,bool synchronous)352 int swap_readpage(struct page *page, bool synchronous)
353 {
354 struct bio *bio;
355 int ret = 0;
356 struct swap_info_struct *sis = page_swap_info(page);
357 blk_qc_t qc;
358 struct gendisk *disk;
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 if (frontswap_load(page) == 0) {
364 SetPageUptodate(page);
365 unlock_page(page);
366 goto out;
367 }
368
369 if (sis->flags & SWP_FILE) {
370 struct file *swap_file = sis->swap_file;
371 struct address_space *mapping = swap_file->f_mapping;
372
373 ret = mapping->a_ops->readpage(swap_file, page);
374 if (!ret)
375 count_vm_event(PSWPIN);
376 return ret;
377 }
378
379 ret = bdev_read_page(sis->bdev, swap_page_sector(page), page);
380 if (!ret) {
381 if (trylock_page(page)) {
382 swap_slot_free_notify(page);
383 unlock_page(page);
384 }
385
386 count_vm_event(PSWPIN);
387 return 0;
388 }
389
390 ret = 0;
391 bio = get_swap_bio(GFP_KERNEL, page, end_swap_bio_read);
392 if (bio == NULL) {
393 unlock_page(page);
394 ret = -ENOMEM;
395 goto out;
396 }
397 disk = bio->bi_disk;
398 /*
399 * Keep this task valid during swap readpage because the oom killer may
400 * attempt to access it in the page fault retry time check.
401 */
402 get_task_struct(current);
403 bio->bi_private = current;
404 bio_set_op_attrs(bio, REQ_OP_READ, 0);
405 count_vm_event(PSWPIN);
406 bio_get(bio);
407 qc = submit_bio(bio);
408 while (synchronous) {
409 set_current_state(TASK_UNINTERRUPTIBLE);
410 if (!READ_ONCE(bio->bi_private))
411 break;
412
413 if (!blk_poll(disk->queue, qc))
414 break;
415 }
416 __set_current_state(TASK_RUNNING);
417 bio_put(bio);
418
419 out:
420 return ret;
421 }
422
swap_set_page_dirty(struct page * page)423 int swap_set_page_dirty(struct page *page)
424 {
425 struct swap_info_struct *sis = page_swap_info(page);
426
427 if (sis->flags & SWP_FILE) {
428 struct address_space *mapping = sis->swap_file->f_mapping;
429
430 VM_BUG_ON_PAGE(!PageSwapCache(page), page);
431 return mapping->a_ops->set_page_dirty(page);
432 } else {
433 return __set_page_dirty_no_writeback(page);
434 }
435 }
436