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 <asm/pgtable.h>
26
27static struct bio *get_swap_bio(gfp_t gfp_flags,
28				struct page *page, bio_end_io_t end_io)
29{
30	struct bio *bio;
31
32	bio = bio_alloc(gfp_flags, 1);
33	if (bio) {
34		bio->bi_iter.bi_sector = map_swap_page(page, &bio->bi_bdev);
35		bio->bi_iter.bi_sector <<= PAGE_SHIFT - 9;
36		bio->bi_io_vec[0].bv_page = page;
37		bio->bi_io_vec[0].bv_len = PAGE_SIZE;
38		bio->bi_io_vec[0].bv_offset = 0;
39		bio->bi_vcnt = 1;
40		bio->bi_iter.bi_size = PAGE_SIZE;
41		bio->bi_end_io = end_io;
42	}
43	return bio;
44}
45
46void end_swap_bio_write(struct bio *bio, int err)
47{
48	const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
49	struct page *page = bio->bi_io_vec[0].bv_page;
50
51	if (!uptodate) {
52		SetPageError(page);
53		/*
54		 * We failed to write the page out to swap-space.
55		 * Re-dirty the page in order to avoid it being reclaimed.
56		 * Also print a dire warning that things will go BAD (tm)
57		 * very quickly.
58		 *
59		 * Also clear PG_reclaim to avoid rotate_reclaimable_page()
60		 */
61		set_page_dirty(page);
62		printk(KERN_ALERT "Write-error on swap-device (%u:%u:%Lu)\n",
63				imajor(bio->bi_bdev->bd_inode),
64				iminor(bio->bi_bdev->bd_inode),
65				(unsigned long long)bio->bi_iter.bi_sector);
66		ClearPageReclaim(page);
67	}
68	end_page_writeback(page);
69	bio_put(bio);
70}
71
72void end_swap_bio_read(struct bio *bio, int err)
73{
74	const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
75	struct page *page = bio->bi_io_vec[0].bv_page;
76
77	if (!uptodate) {
78		SetPageError(page);
79		ClearPageUptodate(page);
80		printk(KERN_ALERT "Read-error on swap-device (%u:%u:%Lu)\n",
81				imajor(bio->bi_bdev->bd_inode),
82				iminor(bio->bi_bdev->bd_inode),
83				(unsigned long long)bio->bi_iter.bi_sector);
84		goto out;
85	}
86
87	SetPageUptodate(page);
88
89	/*
90	 * There is no guarantee that the page is in swap cache - the software
91	 * suspend code (at least) uses end_swap_bio_read() against a non-
92	 * swapcache page.  So we must check PG_swapcache before proceeding with
93	 * this optimization.
94	 */
95	if (likely(PageSwapCache(page))) {
96		struct swap_info_struct *sis;
97
98		sis = page_swap_info(page);
99		if (sis->flags & SWP_BLKDEV) {
100			/*
101			 * The swap subsystem performs lazy swap slot freeing,
102			 * expecting that the page will be swapped out again.
103			 * So we can avoid an unnecessary write if the page
104			 * isn't redirtied.
105			 * This is good for real swap storage because we can
106			 * reduce unnecessary I/O and enhance wear-leveling
107			 * if an SSD is used as the as swap device.
108			 * But if in-memory swap device (eg zram) is used,
109			 * this causes a duplicated copy between uncompressed
110			 * data in VM-owned memory and compressed data in
111			 * zram-owned memory.  So let's free zram-owned memory
112			 * and make the VM-owned decompressed page *dirty*,
113			 * so the page should be swapped out somewhere again if
114			 * we again wish to reclaim it.
115			 */
116			struct gendisk *disk = sis->bdev->bd_disk;
117			if (disk->fops->swap_slot_free_notify) {
118				swp_entry_t entry;
119				unsigned long offset;
120
121				entry.val = page_private(page);
122				offset = swp_offset(entry);
123
124				SetPageDirty(page);
125				disk->fops->swap_slot_free_notify(sis->bdev,
126						offset);
127			}
128		}
129	}
130
131out:
132	unlock_page(page);
133	bio_put(bio);
134}
135
136int generic_swapfile_activate(struct swap_info_struct *sis,
137				struct file *swap_file,
138				sector_t *span)
139{
140	struct address_space *mapping = swap_file->f_mapping;
141	struct inode *inode = mapping->host;
142	unsigned blocks_per_page;
143	unsigned long page_no;
144	unsigned blkbits;
145	sector_t probe_block;
146	sector_t last_block;
147	sector_t lowest_block = -1;
148	sector_t highest_block = 0;
149	int nr_extents = 0;
150	int ret;
151
152	blkbits = inode->i_blkbits;
153	blocks_per_page = PAGE_SIZE >> blkbits;
154
155	/*
156	 * Map all the blocks into the extent list.  This code doesn't try
157	 * to be very smart.
158	 */
159	probe_block = 0;
160	page_no = 0;
161	last_block = i_size_read(inode) >> blkbits;
162	while ((probe_block + blocks_per_page) <= last_block &&
163			page_no < sis->max) {
164		unsigned block_in_page;
165		sector_t first_block;
166
167		first_block = bmap(inode, probe_block);
168		if (first_block == 0)
169			goto bad_bmap;
170
171		/*
172		 * It must be PAGE_SIZE aligned on-disk
173		 */
174		if (first_block & (blocks_per_page - 1)) {
175			probe_block++;
176			goto reprobe;
177		}
178
179		for (block_in_page = 1; block_in_page < blocks_per_page;
180					block_in_page++) {
181			sector_t block;
182
183			block = bmap(inode, probe_block + block_in_page);
184			if (block == 0)
185				goto bad_bmap;
186			if (block != first_block + block_in_page) {
187				/* Discontiguity */
188				probe_block++;
189				goto reprobe;
190			}
191		}
192
193		first_block >>= (PAGE_SHIFT - blkbits);
194		if (page_no) {	/* exclude the header page */
195			if (first_block < lowest_block)
196				lowest_block = first_block;
197			if (first_block > highest_block)
198				highest_block = first_block;
199		}
200
201		/*
202		 * We found a PAGE_SIZE-length, PAGE_SIZE-aligned run of blocks
203		 */
204		ret = add_swap_extent(sis, page_no, 1, first_block);
205		if (ret < 0)
206			goto out;
207		nr_extents += ret;
208		page_no++;
209		probe_block += blocks_per_page;
210reprobe:
211		continue;
212	}
213	ret = nr_extents;
214	*span = 1 + highest_block - lowest_block;
215	if (page_no == 0)
216		page_no = 1;	/* force Empty message */
217	sis->max = page_no;
218	sis->pages = page_no - 1;
219	sis->highest_bit = page_no - 1;
220out:
221	return ret;
222bad_bmap:
223	printk(KERN_ERR "swapon: swapfile has holes\n");
224	ret = -EINVAL;
225	goto out;
226}
227
228/*
229 * We may have stale swap cache pages in memory: notice
230 * them here and get rid of the unnecessary final write.
231 */
232int swap_writepage(struct page *page, struct writeback_control *wbc)
233{
234	int ret = 0;
235
236	if (try_to_free_swap(page)) {
237		unlock_page(page);
238		goto out;
239	}
240	if (frontswap_store(page) == 0) {
241		set_page_writeback(page);
242		unlock_page(page);
243		end_page_writeback(page);
244		goto out;
245	}
246	ret = __swap_writepage(page, wbc, end_swap_bio_write);
247out:
248	return ret;
249}
250
251static sector_t swap_page_sector(struct page *page)
252{
253	return (sector_t)__page_file_index(page) << (PAGE_CACHE_SHIFT - 9);
254}
255
256int __swap_writepage(struct page *page, struct writeback_control *wbc,
257	void (*end_write_func)(struct bio *, int))
258{
259	struct bio *bio;
260	int ret, rw = WRITE;
261	struct swap_info_struct *sis = page_swap_info(page);
262
263	if (sis->flags & SWP_FILE) {
264		struct kiocb kiocb;
265		struct file *swap_file = sis->swap_file;
266		struct address_space *mapping = swap_file->f_mapping;
267		struct bio_vec bv = {
268			.bv_page = page,
269			.bv_len  = PAGE_SIZE,
270			.bv_offset = 0
271		};
272		struct iov_iter from;
273
274		iov_iter_bvec(&from, ITER_BVEC | WRITE, &bv, 1, PAGE_SIZE);
275		init_sync_kiocb(&kiocb, swap_file);
276		kiocb.ki_pos = page_file_offset(page);
277
278		set_page_writeback(page);
279		unlock_page(page);
280		ret = mapping->a_ops->direct_IO(&kiocb, &from, kiocb.ki_pos);
281		if (ret == PAGE_SIZE) {
282			count_vm_event(PSWPOUT);
283			ret = 0;
284		} else {
285			/*
286			 * In the case of swap-over-nfs, this can be a
287			 * temporary failure if the system has limited
288			 * memory for allocating transmit buffers.
289			 * Mark the page dirty and avoid
290			 * rotate_reclaimable_page but rate-limit the
291			 * messages but do not flag PageError like
292			 * the normal direct-to-bio case as it could
293			 * be temporary.
294			 */
295			set_page_dirty(page);
296			ClearPageReclaim(page);
297			pr_err_ratelimited("Write error on dio swapfile (%Lu)\n",
298				page_file_offset(page));
299		}
300		end_page_writeback(page);
301		return ret;
302	}
303
304	ret = bdev_write_page(sis->bdev, swap_page_sector(page), page, wbc);
305	if (!ret) {
306		count_vm_event(PSWPOUT);
307		return 0;
308	}
309
310	ret = 0;
311	bio = get_swap_bio(GFP_NOIO, page, end_write_func);
312	if (bio == NULL) {
313		set_page_dirty(page);
314		unlock_page(page);
315		ret = -ENOMEM;
316		goto out;
317	}
318	if (wbc->sync_mode == WB_SYNC_ALL)
319		rw |= REQ_SYNC;
320	count_vm_event(PSWPOUT);
321	set_page_writeback(page);
322	unlock_page(page);
323	submit_bio(rw, bio);
324out:
325	return ret;
326}
327
328int swap_readpage(struct page *page)
329{
330	struct bio *bio;
331	int ret = 0;
332	struct swap_info_struct *sis = page_swap_info(page);
333
334	VM_BUG_ON_PAGE(!PageLocked(page), page);
335	VM_BUG_ON_PAGE(PageUptodate(page), page);
336	if (frontswap_load(page) == 0) {
337		SetPageUptodate(page);
338		unlock_page(page);
339		goto out;
340	}
341
342	if (sis->flags & SWP_FILE) {
343		struct file *swap_file = sis->swap_file;
344		struct address_space *mapping = swap_file->f_mapping;
345
346		ret = mapping->a_ops->readpage(swap_file, page);
347		if (!ret)
348			count_vm_event(PSWPIN);
349		return ret;
350	}
351
352	ret = bdev_read_page(sis->bdev, swap_page_sector(page), page);
353	if (!ret) {
354		count_vm_event(PSWPIN);
355		return 0;
356	}
357
358	ret = 0;
359	bio = get_swap_bio(GFP_KERNEL, page, end_swap_bio_read);
360	if (bio == NULL) {
361		unlock_page(page);
362		ret = -ENOMEM;
363		goto out;
364	}
365	count_vm_event(PSWPIN);
366	submit_bio(READ, bio);
367out:
368	return ret;
369}
370
371int swap_set_page_dirty(struct page *page)
372{
373	struct swap_info_struct *sis = page_swap_info(page);
374
375	if (sis->flags & SWP_FILE) {
376		struct address_space *mapping = sis->swap_file->f_mapping;
377		return mapping->a_ops->set_page_dirty(page);
378	} else {
379		return __set_page_dirty_no_writeback(page);
380	}
381}
382