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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 
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 	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, thp_size(page), 0);
44 	}
45 	return bio;
46 }
47 
end_swap_bio_write(struct bio * bio)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 
swap_slot_free_notify(struct page * page)72 static void swap_slot_free_notify(struct page *page)
73 {
74 	struct swap_info_struct *sis;
75 	struct gendisk *disk;
76 	swp_entry_t entry;
77 
78 	/*
79 	 * There is no guarantee that the page is in swap cache - the software
80 	 * suspend code (at least) uses end_swap_bio_read() against a non-
81 	 * swapcache page.  So we must check PG_swapcache before proceeding with
82 	 * this optimization.
83 	 */
84 	if (unlikely(!PageSwapCache(page)))
85 		return;
86 
87 	sis = page_swap_info(page);
88 	if (data_race(!(sis->flags & SWP_BLKDEV)))
89 		return;
90 
91 	/*
92 	 * The swap subsystem performs lazy swap slot freeing,
93 	 * expecting that the page will be swapped out again.
94 	 * So we can avoid an unnecessary write if the page
95 	 * isn't redirtied.
96 	 * This is good for real swap storage because we can
97 	 * reduce unnecessary I/O and enhance wear-leveling
98 	 * if an SSD is used as the as swap device.
99 	 * But if in-memory swap device (eg zram) is used,
100 	 * this causes a duplicated copy between uncompressed
101 	 * data in VM-owned memory and compressed data in
102 	 * zram-owned memory.  So let's free zram-owned memory
103 	 * and make the VM-owned decompressed page *dirty*,
104 	 * so the page should be swapped out somewhere again if
105 	 * we again wish to reclaim it.
106 	 */
107 	disk = sis->bdev->bd_disk;
108 	entry.val = page_private(page);
109 	if (disk->fops->swap_slot_free_notify && __swap_count(entry) == 1) {
110 		unsigned long offset;
111 
112 		offset = swp_offset(entry);
113 
114 		SetPageDirty(page);
115 		disk->fops->swap_slot_free_notify(sis->bdev,
116 				offset);
117 	}
118 }
119 
end_swap_bio_read(struct bio * bio)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 	if (waiter) {
141 		blk_wake_io_task(waiter);
142 		put_task_struct(waiter);
143 	}
144 }
145 
generic_swapfile_activate(struct swap_info_struct * sis,struct file * swap_file,sector_t * span)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 tree.  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 = probe_block;
180 		ret = bmap(inode, &first_block);
181 		if (ret || !first_block)
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 = probe_block + block_in_page;
197 			ret = bmap(inode, &block);
198 			if (ret || !block)
199 				goto bad_bmap;
200 
201 			if (block != first_block + block_in_page) {
202 				/* Discontiguity */
203 				probe_block++;
204 				goto reprobe;
205 			}
206 		}
207 
208 		first_block >>= (PAGE_SHIFT - blkbits);
209 		if (page_no) {	/* exclude the header page */
210 			if (first_block < lowest_block)
211 				lowest_block = first_block;
212 			if (first_block > highest_block)
213 				highest_block = first_block;
214 		}
215 
216 		/*
217 		 * We found a PAGE_SIZE-length, PAGE_SIZE-aligned run of blocks
218 		 */
219 		ret = add_swap_extent(sis, page_no, 1, first_block);
220 		if (ret < 0)
221 			goto out;
222 		nr_extents += ret;
223 		page_no++;
224 		probe_block += blocks_per_page;
225 reprobe:
226 		continue;
227 	}
228 	ret = nr_extents;
229 	*span = 1 + highest_block - lowest_block;
230 	if (page_no == 0)
231 		page_no = 1;	/* force Empty message */
232 	sis->max = page_no;
233 	sis->pages = page_no - 1;
234 	sis->highest_bit = page_no - 1;
235 out:
236 	return ret;
237 bad_bmap:
238 	pr_err("swapon: swapfile has holes\n");
239 	ret = -EINVAL;
240 	goto out;
241 }
242 
243 /*
244  * We may have stale swap cache pages in memory: notice
245  * them here and get rid of the unnecessary final write.
246  */
swap_writepage(struct page * page,struct writeback_control * wbc)247 int swap_writepage(struct page *page, struct writeback_control *wbc)
248 {
249 	int ret = 0;
250 
251 	if (try_to_free_swap(page)) {
252 		unlock_page(page);
253 		goto out;
254 	}
255 	/*
256 	 * Arch code may have to preserve more data than just the page
257 	 * contents, e.g. memory tags.
258 	 */
259 	ret = arch_prepare_to_swap(page);
260 	if (ret) {
261 		set_page_dirty(page);
262 		unlock_page(page);
263 		goto out;
264 	}
265 	if (frontswap_store(page) == 0) {
266 		set_page_writeback(page);
267 		unlock_page(page);
268 		end_page_writeback(page);
269 		goto out;
270 	}
271 	ret = __swap_writepage(page, wbc, end_swap_bio_write);
272 out:
273 	return ret;
274 }
275 
count_swpout_vm_event(struct page * page)276 static inline void count_swpout_vm_event(struct page *page)
277 {
278 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
279 	if (unlikely(PageTransHuge(page)))
280 		count_vm_event(THP_SWPOUT);
281 #endif
282 	count_vm_events(PSWPOUT, thp_nr_pages(page));
283 }
284 
285 #if defined(CONFIG_MEMCG) && defined(CONFIG_BLK_CGROUP)
bio_associate_blkg_from_page(struct bio * bio,struct page * page)286 static void bio_associate_blkg_from_page(struct bio *bio, struct page *page)
287 {
288 	struct cgroup_subsys_state *css;
289 
290 	if (!page->mem_cgroup)
291 		return;
292 
293 	rcu_read_lock();
294 	css = cgroup_e_css(page->mem_cgroup->css.cgroup, &io_cgrp_subsys);
295 	bio_associate_blkg_from_css(bio, css);
296 	rcu_read_unlock();
297 }
298 #else
299 #define bio_associate_blkg_from_page(bio, page)		do { } while (0)
300 #endif /* CONFIG_MEMCG && CONFIG_BLK_CGROUP */
301 
__swap_writepage(struct page * page,struct writeback_control * wbc,bio_end_io_t end_write_func)302 int __swap_writepage(struct page *page, struct writeback_control *wbc,
303 		bio_end_io_t end_write_func)
304 {
305 	struct bio *bio;
306 	int ret;
307 	struct swap_info_struct *sis = page_swap_info(page);
308 
309 	VM_BUG_ON_PAGE(!PageSwapCache(page), page);
310 	if (data_race(sis->flags & SWP_FS_OPS)) {
311 		struct kiocb kiocb;
312 		struct file *swap_file = sis->swap_file;
313 		struct address_space *mapping = swap_file->f_mapping;
314 		struct bio_vec bv = {
315 			.bv_page = page,
316 			.bv_len  = PAGE_SIZE,
317 			.bv_offset = 0
318 		};
319 		struct iov_iter from;
320 
321 		iov_iter_bvec(&from, WRITE, &bv, 1, PAGE_SIZE);
322 		init_sync_kiocb(&kiocb, swap_file);
323 		kiocb.ki_pos = page_file_offset(page);
324 
325 		set_page_writeback(page);
326 		unlock_page(page);
327 		ret = mapping->a_ops->direct_IO(&kiocb, &from);
328 		if (ret == PAGE_SIZE) {
329 			count_vm_event(PSWPOUT);
330 			ret = 0;
331 		} else {
332 			/*
333 			 * In the case of swap-over-nfs, this can be a
334 			 * temporary failure if the system has limited
335 			 * memory for allocating transmit buffers.
336 			 * Mark the page dirty and avoid
337 			 * rotate_reclaimable_page but rate-limit the
338 			 * messages but do not flag PageError like
339 			 * the normal direct-to-bio case as it could
340 			 * be temporary.
341 			 */
342 			set_page_dirty(page);
343 			ClearPageReclaim(page);
344 			pr_err_ratelimited("Write error on dio swapfile (%llu)\n",
345 					   page_file_offset(page));
346 		}
347 		end_page_writeback(page);
348 		return ret;
349 	}
350 
351 	ret = bdev_write_page(sis->bdev, swap_page_sector(page), page, wbc);
352 	if (!ret) {
353 		count_swpout_vm_event(page);
354 		return 0;
355 	}
356 
357 	bio = get_swap_bio(GFP_NOIO, page, end_write_func);
358 	if (bio == NULL) {
359 		set_page_dirty(page);
360 		unlock_page(page);
361 		return -ENOMEM;
362 	}
363 	bio->bi_opf = REQ_OP_WRITE | REQ_SWAP | wbc_to_write_flags(wbc);
364 	bio_associate_blkg_from_page(bio, page);
365 	count_swpout_vm_event(page);
366 	set_page_writeback(page);
367 	unlock_page(page);
368 	submit_bio(bio);
369 
370 	return 0;
371 }
372 
swap_readpage(struct page * page,bool synchronous)373 int swap_readpage(struct page *page, bool synchronous)
374 {
375 	struct bio *bio;
376 	int ret = 0;
377 	struct swap_info_struct *sis = page_swap_info(page);
378 	blk_qc_t qc;
379 	struct gendisk *disk;
380 	unsigned long pflags;
381 
382 	VM_BUG_ON_PAGE(!PageSwapCache(page) && !synchronous, page);
383 	VM_BUG_ON_PAGE(!PageLocked(page), page);
384 	VM_BUG_ON_PAGE(PageUptodate(page), page);
385 
386 	/*
387 	 * Count submission time as memory stall. When the device is congested,
388 	 * or the submitting cgroup IO-throttled, submission can be a
389 	 * significant part of overall IO time.
390 	 */
391 	psi_memstall_enter(&pflags);
392 
393 	if (frontswap_load(page) == 0) {
394 		SetPageUptodate(page);
395 		unlock_page(page);
396 		goto out;
397 	}
398 
399 	if (data_race(sis->flags & SWP_FS_OPS)) {
400 		struct file *swap_file = sis->swap_file;
401 		struct address_space *mapping = swap_file->f_mapping;
402 
403 		ret = mapping->a_ops->readpage(swap_file, page);
404 		if (!ret)
405 			count_vm_event(PSWPIN);
406 		goto out;
407 	}
408 
409 	if (sis->flags & SWP_SYNCHRONOUS_IO) {
410 		ret = bdev_read_page(sis->bdev, swap_page_sector(page), page);
411 		if (!ret) {
412 			if (trylock_page(page)) {
413 				swap_slot_free_notify(page);
414 				unlock_page(page);
415 			}
416 
417 			count_vm_event(PSWPIN);
418 			goto out;
419 		}
420 	}
421 
422 	ret = 0;
423 	bio = get_swap_bio(GFP_KERNEL, page, end_swap_bio_read);
424 	if (bio == NULL) {
425 		unlock_page(page);
426 		ret = -ENOMEM;
427 		goto out;
428 	}
429 	disk = bio->bi_disk;
430 	/*
431 	 * Keep this task valid during swap readpage because the oom killer may
432 	 * attempt to access it in the page fault retry time check.
433 	 */
434 	bio_set_op_attrs(bio, REQ_OP_READ, 0);
435 	if (synchronous) {
436 		bio->bi_opf |= REQ_HIPRI;
437 		get_task_struct(current);
438 		bio->bi_private = current;
439 	}
440 	count_vm_event(PSWPIN);
441 	bio_get(bio);
442 	qc = submit_bio(bio);
443 	while (synchronous) {
444 		set_current_state(TASK_UNINTERRUPTIBLE);
445 		if (!READ_ONCE(bio->bi_private))
446 			break;
447 
448 		if (!blk_poll(disk->queue, qc, true))
449 			blk_io_schedule();
450 	}
451 	__set_current_state(TASK_RUNNING);
452 	bio_put(bio);
453 
454 out:
455 	psi_memstall_leave(&pflags);
456 	return ret;
457 }
458 
swap_set_page_dirty(struct page * page)459 int swap_set_page_dirty(struct page *page)
460 {
461 	struct swap_info_struct *sis = page_swap_info(page);
462 
463 	if (data_race(sis->flags & SWP_FS_OPS)) {
464 		struct address_space *mapping = sis->swap_file->f_mapping;
465 
466 		VM_BUG_ON_PAGE(!PageSwapCache(page), page);
467 		return mapping->a_ops->set_page_dirty(page);
468 	} else {
469 		return __set_page_dirty_no_writeback(page);
470 	}
471 }
472